NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Oahu Wind Integration and 

Transmission Study (OWITS) 

Hawaiian Islands Transmission 

Interconnection Project 

Dennis Woodford

Electranix Corporation

Winnipeg, Manitoba Canada

Subcontract Report

NREL/SR-5500-50411 

February 2011
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Oahu Wind Integration and 

Transmission Study (OWITS) 

Hawaiian Islands Transmission 

Interconnection Project 

Dennis Woodford

Electranix Corporation

Winnipeg, Manitoba Canada

NREL Technical Monitor: David Corbus

Prepared under Subcontract No. LAM-9-99436-01

Subcontract Report

NREL/SR-5500-50411 

February 2011
This publication was reproduced from the best available copy

submitted by the subcontractor and received no editorial review at NREL.

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Executive Summary

In October 2008, the State of Hawaii and the Hawaiian Electric Companies entered into the 

Hawaii Clean Energy Agreement to move Hawaii off of its dependence on imported fossil 

fuels for electricity and transportation. The U.S. Department of Energy contracted R.W. 

Beck in 2008 to evaluate interconnection of the transmission systems of the islands of Lanai, 

Molokai and Maui with Oahu. Phase I of this independent review included an initial 

evaluation of the technical configuration and capital costs of establishing an undersea cable 

system and examining impacts to the existing electric transmission systems as a result of

interconnecting the islands. To move forward from the foundational work of the R.W. Beck 

report [1] and in support of the Hawaiian Clean Energy Agreement, the Department of 

Energy through the National Renewable Energy Laboratory contracted Electranix 

Corporation to study the undersea cable system necessary to transmit 400 MW of wind 

energy from the islands of Lanai and/or Molokai to Oahu (Stage 1) and the future installation 

of a 200-MW capacity cable system to interconnect the island of Maui (Stage 2). 

The study effort included a technical feasibility assessment and budgetary cost estimate of the 

undersea transmission interconnect options. Inputs from the suppliers of undersea power 

cables and direct current (DC) converter station has been provided. Six DC cable options and 

one AC cable option were selected from 18 alternative configurations were developed by 

building on the R.W. Beck study [1]. Only one of the selected options included undersea 

cable transmission between Lanai and Molokai whereas all the alternatives from this previous 

study included undersea cable transmission between the two islands. The economic 

justification for undersea cable transmission between Lanai and Molokai could not easily be 

established, so the feed to Oahu from these islands was radial only. 

The AC option was only considered viable if three core XLPE cable can be applied, but 

which is limited by the depth to which it can be laid because of its weight. Consequently it is 

precluded for feeding into Oahu. However, it could be used to interconnect Molokai and 

Lanai and even to Maui, and which was investigated for one option. For long AC undersea 

cables, the three core XLPE cable is the most viable configuration since having the three 

phase conductors as close together as possible results in significant cancellation of the 

magnetic field generated by the phase currents. Eddy currents and other induced currents in 

the shield and armor conductors of the cable are minimized allowing low induced cable
losses. Alternate use of three separate single core cables will result in higher losses in the 

shields and armors since there is no cancellation of the magnetic field generated by the phase 

currents unless the three cables are lashed and laid together.

The technology for the six selected DC options is voltage sourced converters (VSC). VSC 

can create a stable AC supply for wind turbine generators to connect into. They also offer a 

significant buffer to AC system faults at one end adversely impacting the AC system at the 

other end. The wind turbine generators on Molokai and Lanai will not be affected 

significantly by severe AC system faults on Oahu.

With a suitable control strategy for the VSC transmission, it will be possible to maintain a 

steady AC voltage and frequency for the sending end wind farms. This means that a direct 

and conventional interconnection to the small local load on Molokai or Lanai may be 

possible. It is only when the DC cable transmission is completely taken out of service that the 

interconnection to local load would have to be transfer tripped. 

The capital costs for the six selected DC cable transmission options are assembled from the 

responses of the cable and equipment suppliers. The stated accuracy of these costs is ±20%, 

and so the estimated values are the lowest provided by the suppliers plus 20%. Case A1-2(a) 

has a 200-MW DC connection between Lanai and Molokai and Case A1-2(b) has a 200-MW 

AC connection between Molokai and Lanai, which is slightly lower cost. Analysis (Appendix 

A) indicates additional justification will be needed to consider a Molokai to Lanai 

interconnection for Stage 1 development. 

An independent option was proposed by one of the equipment suppliers whose significant 

benefit is the termination of the Stage 2 transmission from Maui at Lanai or Molokai instead 

of at Oahu as in the selected options in Table 1. Capital costs are therefore lower because less 

undersea cable is required, but suffers the disadvantage that power scheduled to Oahu from 

Maui would only be at the level possible when the wind power being generated on Lanai 

(and/or Molokai) is below full rating. Power schedules from Oahu to Maui on the other hand 

would not be restricted below the capacity limits of the converters and undersea cable 

transmission since any wind power being generated on Lanai and/or Molokai would be 

displaced accordingly. 
Table 1: Budgetary capital Costs in 2009 millions of dollars as provided by suppliers of DC 

cable and DC converter equipment for the DC Options. 

Option C3-2 A3-2 A1-2 B3-2 C1-2 B1-2

Description 400 MW 

Koolau 

to 

Molokai 

200 MW 

Molokai to 

Koolau, 200

MW Molokai 

to Iwilei

200 MW 

Molokai to 

Koolau, 200

MW Lanai to 

Iwilei, 200MW 

Lanai to Molokai

400 MW 

Molokai 

to Iwilei 

200 MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau

200 MW 

Molokai to 

Iwilei, 200 

MW Lanai 

to Iwilei

(a) (b)

Stations $M 234 288 414 342 234 288 288

Cables $M 154 180 367 424 221 216 245

Total Stage 

1 Price $M

388 468 781 766 455 504 533

Stage 2 

Maui to 

Oahu 

(Approx)

Converter 

Stations $M

144 144 117 117 144 144 144

DC Cables 

$M

420 420 192 192 283 272 272

Total Stage 

2 Price $M

564 564 309 309 427 416 416

Total Stages 

1 & 2 $M

951 1,032 1,090 1,077 882 920 949

The level of power schedules into or out of the HECO system on Oahu are restrained to the 

maximum single contingency outage possible, which for this study is 200 MW [2]. Rating the 

converters and cables above this level is certainly possible and perhaps desirable but requires 

further investigation.

From a technical perspective, the VSC cable transmission applied to these DC Options is 

completely viable with little risk of significant problems that would impede its use. The 

technology is being used to other similar projects of similar rating such as the BorWin Alpha 

400-MW offshore wind farm in the North Sea1

. 

 

1 The BorWin Alpha 400-MW project in the North Sea feeds offshore wind energy into Germany. This includes 

125 km of undersea cables and 75 km of underground cable at ±150 kV using ABB’s HVDC Light technology. 

The platform AC voltage is transformed to 170 kV from the 36-kV AC collector system cables from the wind 

turbine generators. It feeds into the onshore substation at Diele at 400-kV AC. It was commissioned late in 2009.
Acknowledgements

Appreciation is expressed for the support of Dave Corbus of NREL along with the team who 

met regularly to provide suggestions and directions. This includes Leon Roose, Marc 

Matsuura, Dora Nakafuji, Dave Burlingame, Dean Arakawa and Matt Schuerger.

Appreciation is also expressed for the support from Josh Strickler of the Department of 

Business, Economic Development and Tourism and Sandy Shor of the School of Ocean and 

Earth Science and Technology of who facilitated and provided the seabed data for the cable 

costing.
Table of Contents

EXECUTIVE SUMMARY .............................................................................................................................. - 1 -

Acknowledgements.................................................................................................................................... - 4 -

TABLE OF CONTENTS ................................................................................................................................. - 6 -

INTRODUCTION ............................................................................................................................................ - 8 -

UNDERSEA CABLE OPTIONS..................................................................................................................... - 8 -

TECHNICAL OPTIONS FOR AC AND DC CABLES ............................................................................................. - 8 -

SELECTED HVDC OPTIONS .......................................................................................................................... - 10 -

AC CABLE OPTION....................................................................................................................................... - 15 -

ENVIRONMENTAL CONSIDERATIONS ............................................................................................................ - 17 -

RELIABILITY CONSIDERATIONS .................................................................................................................... - 17 -

LOSS CONSIDERATIONS ................................................................................................................................ - 18 -

FUTURE CONNECTION TO MAUI ................................................................................................................... - 18 -

CAPITAL COSTS ASSESSMENT............................................................................................................... - 19 -

ACCURACY OF COSTS PROVIDED.................................................................................................................. - 19 -

RANGE OF COSTS FOR TERMINATING SUBSTATIONS..................................................................................... - 19 -

COSTS FOR DC CONVERTER STATION OPTIONS............................................................................................ - 20 -

CAPITAL COST EVALUATION OF CABLE OPTIONS......................................................................................... - 21 -

CONSIDERATION FOR 400 MW WIND GENERATION ON LANAI..................................................................... - 22 -

IMPACT OF LOSSES ....................................................................................................................................... - 23 -

IMPACT OF RELIABILITY ............................................................................................................................... - 24 -

RISK ............................................................................................................................................................. - 24 -

LIFE CYCLE COSTS ....................................................................................................................................... - 25 -

INDEPENDENT OPTION.................................................................................................................................. - 27 -

TECHNICAL STUDY ................................................................................................................................... - 30 -

OBJECTIVES.................................................................................................................................................. - 31 -

STUDY CONSIDERATIONS ............................................................................................................................. - 31 -

VSC CONVERTER CONTROL STRATEGY ....................................................................................................... - 31 -

MOST SEVERE SINGLE CONTINGENCY DISTURBANCE .................................................................................. - 33 -

IMPACT OF FAULTS ON OAHU ON THE WIND TURBINE GENERATORS ........................................................... - 34 -

IMPACT OF AC FAULTS ON MOLOKAI OR LANAI ON THE HECO GRID ON OAHU ......................................... - 34 -

CONNECTION TO LOCAL LOAD ON MOLOKAI OR LANAI............................................................ - 35 -

CONCLUSIONS............................................................................................................................................. - 36 -

REFERENCES ............................................................................................................................................... - 37 -

LIST OF APPENDICES................................................................................................................................ - 38 -

APPENDIX A: SELECTION OF PREFERRED OPTIONS FOR THE INTER-ISLAND TRANSMISSION......................... - 38 -

APPENDIX B: EVALUATION OF SVC REQUIREMENT FOR INTER-ISLAND AC CABLE OPTION........................ - 38 -

APPENDIX C: SIMULATION STUDIES FOR INTER-ISLAND DC CABLE OPTIONS.............................................. - 38 -

APPENDIX D: REQUEST FOR INFORMATION FROM DC CONVERTER AND CABLE MANUFACTURERS............. - 38 -

APPENDIX A.................................................................................................................................................. - 39 -

SELECTION OF PREFERRED OPTIONS FOR THE INTER-ISLAND TRANSMISSION............................................... - 39 -

Introduction............................................................................................................................................. - 39 -

Impact of Losses...................................................................................................................................... - 40 -

Capital Cost Summary Including Losses ................................................................................................ - 42 -

Description of Preferred Options............................................................................................................ - 43 -

Impact of Reliability................................................................................................................................ - 47 -

Possibility for Spare Cable ..................................................................................................................... - 49 -

Cable Connection Between Lanai and Molokai...................................................................................... - 50 -

Summary ................................................................................................................................................. - 50 -
- 7 -

APPENDIX B.................................................................................................................................................. - 51 -

EVALUATION OF SVC REQUIREMENT FOR INTER-ISLAND AC CABLE OPTION ............................................. - 51 -

Introduction............................................................................................................................................. - 51 -

Modeling ................................................................................................................................................. - 52 -

Overvoltage Control ............................................................................................................................... - 53 -

Conclusions............................................................................................................................................. - 57 -

APPENDIX C.................................................................................................................................................. - 58 -

SIMULATION STUDIES FOR INTER-ISLAND DC CABLE OPTIONS ................................................................... - 58 -

Introduction............................................................................................................................................ - 58 -

APPENDIX D.................................................................................................................................................. - 77 -

PRICING ......................................................................................................................................................... - 83 -

TECHNICAL DATA REQUESTS .............................................................................................................. - 89 -

PRICING ....................................................................................................................................................... - 109 -
- 8 -

Introduction 

High voltage direct current transmission is very much an evolving technology with the 

application of voltage sourced converters (VSC) to cable systems and now to overhead 

transmission. ABB were the pioneers of this technology in the 1990s as it is applied to 

commercial power transmission. Siemens have now entered the market and Areva will be 

able to offer VSC transmission in 2010. 

Using previous studies [1], [2] as a reference, eighteen new transmission options were 

developed from which 6 DC cable options and 1 AC cable option were developed in 

Appendix A for further investigation and costing for electrically interconnecting the 

Hawaiian Islands of Molokai, Lanai and Maui to Oahu. Each supplier of DC converter 

equipment was invited to cost out the converter stations. Seabed data was provided by the 

University of Hawaii School of Ocean and Earth Science and Technology to enable the 

manufacturers of undersea power cables to realistically estimate the costs of laying and 

burying cable (Appendix D). 

The capital costs provided by the suppliers of power cable and converter station equipment 

are summarized and a technical evaluation of the interconnection project is made. 

Undersea Cable Options

Technical Options for AC and DC Cables

The preferred options for undersea cable power transmission to Oahu from Molokai, Lanai 

and Maui were selected based on the options developed in the R.W. Beck report [1] followed 

by an additional study that examined the impact of capital costs, losses and reliability. 

Eighteen inter-island AC and DC transmission options were formulated and analyzed for 

selection of preferred cases (Appendix A) using best available costs for cables and 

converters2

 

2 The Appendix A cost assessments did not use the latest cost information from the equipment suppliers as they 

had not been requested at this stage in the study. Instead best available costs were used to select lowest cost 

options for this initial assessment of 18 cable transmission alternatives.

. Six high-voltage direct current (HVDC) and one alternating current (AC) power 

cable transmission options were selected for further assessment. The most significant 

difference between these new options and the earlier ones developed [1] is that undersea 
- 9 -

cable transmission between Molokai and Lanai is excluded because it was difficult to 

economically justify. Nevertheless one of the new preferred options did include undersea 

cable transmission between Molokai to Lanai. Each is preferred option is divided into two 

stages.

Stage 1: A total of 400 MW terminating on Oahu, originating on Molokai and/or Lanai. This 

would be the stage that would be constructed first.

Stage 2: 200-MW capacity cable connecting Maui to the transmission system constructed in 

Stage 1. This would be constructed at a later time. 

For the purpose of this study and in understanding the HVDC options under consideration, 

two configurations are considered for the converters. Each configuration limits the loss of 

capacity due to a single point of failure to 200 MW which was assumed to apply at all landing 

sites studied on Oahu. This was a requirement since HECO normally operates with 180 MW 

of spinning reserve and an instantaneous loss of 400 MW due to a single point of failure 

would not be acceptable. These are:

1. The 200-MW symmetrical monopole. This is shown in diagram form in Figure 1. It 

consists of a single HVDC converter rated at ±150 kV, and 200 MW and two 

undersea cables. If any one component is faulted, the power transfer is lost. 

Figure 1: HVDC Symmetrical monopole

2. The 400-MW bipole. This is shown in diagram form Figure 2. It consists of two 

identical and independent 200 MW monopoles, one at +150 kV and the other at -150 

kV, with three undersea cables, of which one is grounded at one end that serves as a 

metallic return path when one pole fails. The DC current capacity of the metallic 

return cable is rated to the same level of the pole cables. However, the voltage rating 

can be less.

Figure 2: HVDC bipole 

200 MW Symmetrical Monopole

200 MW 400 MW 

200 MW

400 MW Bipole 
- 10 -

The HVDC converters are voltage sourced converters (VSC). This is the converter 

technology ABB have used for the Cross Sound transmission between Long Island and 

Connecticut (HVDC Light) and which Siemens have applied for the TransBay project 

between Pittsburg, California and San Francisco (HVDC Plus). VSC converters are expected 

to have a life span comparable to conventional thyristor-based HVDC converters of 40 years. 

An advantage in the VSC technology is it allows use of solid insulation undersea cables. They 

are comparatively lower cost than the mass impregnated cables that have been traditionally 

applied for HVDC undersea power transmission, largely for the reason that the solid insulated 

cables are lighter in weight than mass impregnated cables. The suppliers of cables were not 

restrained as to what type of cable to provide when budget costs were requested for this 

application As a consequence, they only proposed solid insulated cables suggesting that they 

would be the lower cost cables to supply. VSC converters can support and even provide an ac 

voltage supply, which is important for connecting wind farms on Molokai and Lanai. Six

VSC projects with solid insulated undersea cables are now in service throughout the world, 

with one project (CrossSound) in service in the U.S. 

For the HVDC bipole configuration of Figure 2, there is a possibility of using pole cables 

with an imbedded neutral. If each high voltage DC cable has an imbedded neutral, then on 

loss of one, the remaining pole cable could continue to support the operation of the healthy 

pole using its imbedded neutral as a metallic return conductor. In this way the third metallic 

return conductor as shown in Figure 2 would not be required as the imbedded neutral 

conductor would serve as the metallic return path. Loss of one cable in a bipolar 

configuration would allow full operation of the other pole through the remaining cable. The 

cost saving in requiring only two cables with imbedded neutral conductors instead of three 

conventional coaxial cables may be offset by the more conductive material needed in each 

cable with imbedded neutrals and the consequential greater weight resulting in limits on 

seabed depth to which it could be laid. 

Selected HVDC Options

With these converter configurations, the selected options for undersea cables are summarized 

visually as follows. More details are available in Appendix A with the assumption that the 
- 11 -

Stage 2 interconnection is rated to 200 MW, and traverses the full distance from Maui to 

Oahu. 

Figure 3: HVDC Option C3-2 

Figure 4: HVDC Option A3-2 

Option A1-2 shown in Figure 5 includes a cable interconnection between the islands of 

Molokai and Lanai. Two alternative cases are proposed, the DC alternative and an AC 

alternative. The DC alternative is a ±150-kV, 200-MW symmetrical bipole and the AC 

alternative is with a 230-kV, three-core XLPE cable. Although the AC interconnection 

between Molokai and Lanai was not studied specifically, the general results and conclusions 

in Appendix B apply. 

200 MW 400 MW 

200 MW 

200 MW 

Iwilei Maui

Molokai 

Koolau

200 MW Symmetrical 

Monopole – Stage 2 

400 MW Bipole – Stage 1

200 MW

Iwilei 200 MW Symmetrical Maui 

Monopole – Stage 2 

400 MW

Molokai

Koolau 

Stage 1 

200 MW Symmetrical Monopole 

200 MW Symmetrical Monopole
- 12 -

Figure 5: HVDC Option A1-2 (a) with DC cable Molokai to Lanai and (b) with AC cable

Figure 6: HVDC Option B3-2 

200 MW

Iwilei 

Maui

200 MW Pole - Stage 2

200 MW

Molokai 

Koolau

Stage 1 

200 MW Symmetrical Monopole

200 MW Pole

Lanai

200MW Symmetrical 

Monopole between Lanai 

and Molokai 

400 MW

200 MW 

Iwilei

Maui

Molokai

Koolau 

200 MW Symmetrical 

Monopole – Stage 2 

400 MW Bipole – Stage 1

200 MW

Iwilei

Maui

200 MW Pole - Stage 2

200 MW 

Molokai 

Koolau

Stage 1

200 MW Symmetrical Monopole 

200 MW Pole

Lanai

200MW AC cable between 

Lanai and Molokai 

(b) AC cable Molokai to Lanai

(b) DC cable Molokai to Lanai
- 13 -

Figure 7: HVDC Option C1-2 

Figure 8: HVDC Option B1-2 

All cables that cross Penguin Bank and the Humpback whale sanctuary (Appendix D) will be 

buried in the seabed. 

Impact of Stage 1 on the later installation of Stage 2 is in being able to anticipate where the 

Stage 2 converter will be eventually located on Oahu. As the Stage 1 converters are located, 

will or should space be left for the future installation of a Stage 2 converter? If the installation 

date of Stage 2 is known with a fair degree of certainty, then the location of its Oahu 

converter can be sited in coordination with the Stage 1 converters. This coordination will 

include the cables associated with each Stage.

Maui

Molokai 

Lanai

200 MW Symmetrical 

Monopole – Stage 2 Iwilei 

2 - 200 MW Symmetrical 

Monopoles – Stage 1 

200 MW 

200 MW 

200 MW

Koolau

200 MW 

200 MW

Iwilei 

600 MW Total 

Maui 

Molokai

200 MW Symmetrical 

Monopole – Stage 2 

200 MW Symmetrical 

Monopole – Stage 1 

Lanai

200 MW Symmetrical 200 MW

Monopole – Stage 1 
- 14 -

Option A1-2 shown in Figure 5 integrates an HVDC bipole between the two stages. This 

concept will be most effective when timing and siting for the converters and cables of each 

stage are known. Then the laying of undersea cable can be coordinated such as deciding 

whether to purchase and lay Stage 1 and 2 cables together or delay the purchase and laying of 

the Stage 2 cables. Option A1-2 takes advantage of extending one pole of a bipole to Maui. 

Such a configuration has been contemplated in previous projects but never applied. It is 

considered acceptable since each pole must be independent to ensure outage or failure is 

contained to just a single pole. The controls of each pole including their synchronization 

would be completely independent. However, currents would flow in the neutral conductor. 

The radial configuration of HVDC feeders to Oahu from Molokai and Lanai means that each 

feeder is independent of Stage 2, with the only exception being Option A1-2 as discussed. 

A limitation on rating of cables and converters is the first contingency outage of 200 MW. If 

it is possible to increase this level in the known future, then it would be possible to 

correspondingly rate the undersea feeder cables to a higher level initially to take advantage of 

this increased first contingency outage level. Larger rated wind farms on Molokai and Lanai 

could be anticipated along with additional HVDC converter capacity. The decision to overrate the cables and converters initially would be subject to study, knowing when and to what 

level the outages can be increased for N-1 survival. 

It is recommended that Stage 1 cable and converter rating continue to be defined by the 

contingency outage of 200 MW unless it is known for certain that a higher level will be 

possible in the foreseeable future. In this case, the HVDC undersea cables could be initially 

rated to this higher level. The HVDC converters could be sized for uprating when needed. 

It is also recommended that Stage 2 be independently developed and constructed if rated to 

200 MW. Where possible, converter station and cable landing space on Oahu should be 

identified and preserved. However, there is a possibility the Stage 2 cable transmission is 

terminated on Lanai or Molokai rather than on Oahu if rated less than 200 MW, and this 

option is considered further in this report.
- 15 -

AC Cable Option

Figure 9 presents a 230-kV AC cable option A1-1. The undersea distances involved are 

relatively long for AC undersea cable transmission but are quite doable if 3 core 230-kV 

cables can be used. The use of solid insulated cables in the form of Cross-linked Polyethylene 

(XLPE) is beneficial in this respect. Each set of cables may be either a single cable with three 

cores imbedded together along with a fiber cable, or as three separate cables laid or lashed 

together. The cables of each of the separate phases need to be close together in order to 

minimize losses in the metallic shields due to magnetic coupling with the current in each 

phase conductor. However, there is difficulty in laying three such cables together if they 

cannot be unloaded from the one ship at the same time. 

In response to a request for information to undersea cable suppliers, it was indicated that the 

use of a single AC cable with three imbedded cores although a lower cost than three separate 

single core cables, was not practical for the depths involved. The heavier weight prevents its 

laying to such depths. However, it is feasible to apply the AC three-core cable in the 

shallower depths between Molokai and Lanai as shown in Figure 5. 

Figure 9: AC Option A1-1 

If AC cables can operate and do so with minimum impact on the wind farms at the sending 

end and on the AC system of HECO on Oahu, they have to be 100% shunt compensated. AC 

cables have very high shunt capacitance that need to be fully counteracted at 60 Hz by fixed 

shunt reactor compensation. However, the AC cables have relatively low series impedance 

compared to overhead transmission lines of similar length and voltage (approximately 30% of 

200 MW

200 MW

Maui

Molokai

Lanai

200 MW 

Iwilei 

Koolau

Stage 2 – 230 kV AC 3 Core Cable

Stage 1- 230 kV AC 3 Core Cable

Stage 1 – 230 kV AC 3 Core Cable
- 16 -

the series impedance of an equivalent overhead line). With reference to Figure 9, the 

electrical distance that the wind farm on Molokai is removed from Oahu with XLPE AC 

cables is equivalent to only 30% of the 40 miles (which is 12 miles) if connected through an 

equivalent 230-kV overhead transmission line. Similarly, the equivalent overhead line 

electrical distance from Lanai to Oahu is 21 miles instead of 70 miles, again because of the 

low series impedance of the undersea AC cables. As a consequence the wind farms at 

Molokai and Lanai connected to Oahu through AC cables would appear electrically close 

except that the impedance of the transformers at each end of the cable adds to the cable 

impedance.

Energizing such a long AC cable would be done from the Oahu end only. It would be 

energized with a special two circuit breaker arrangement together with a series pre-insertion 

resistor. The first circuit breaker closes the pre-insertion resistor to charge up the cable since 

it is resonantly tuned because of being 100% shunt compensated. When the cable has reached 

close to the operating voltage after a number of cycles, the second circuit breaker closes bypassing the resistor and bringing the cable on line such that the AC voltage on the HECO 

system is not transiently disrupted. 

From studies undertaken for the AC cables, the following conclusions are made regarding 

compensation and overvoltage on the AC cable feeders for the wind farms. Only Stage 1 

cable transmission is studied with one radial feeder to Koolau from Molokai and one radial 

feeder to Iwilei from Lanai.

1. Under normal operation, reactive power loading at the connection busbars is quite 

manageable when the AC cables are 100% shunt compensated. No additional facilities

for reactive power are required at either end of the cables to compensate the variations 

in reactive power with variations in power flow through the cable. The normal 

reactive power requirements for a wind farm interconnection should apply at both 

Lanai and Molokai. 

2. The AC cables can be energized virtually transient free with the pre-insertion 

resistance strategy applied, thereby alleviating the need to apply an SVC or 

STATCOM to smooth out voltage transients.
- 17 -

3. When the AC cables are connected to the network and in service, their resonant 

frequency approaches the second harmonic (120 Hz). When an ac fault is cleared near 

either end of the cable, local transformers will saturate. The resulting magnetizing 

currents into these transformers will contain a second harmonic current which can 

cause over-voltages on the cable with a second harmonic resonance. This issue will 

have to be addressed if AC cables are contemplated. Special filters or thyristorswitched metal oxide arresters are options to investigate if harmonic over-voltages are 

possible with the cables selected. 

4. Of concern with the AC undersea cables is the resulting voltage when the cable opens 

up at its receiving end (Oahu end) following a bus fault on the interconnection bus or 

if it inadvertently trips out of service at Oahu. An overvoltage on the cable and on the 

wind farm AC network at the sending end will occur if the wind turbine generators 

stay connected at the sending end. The study on AC cable overvoltage is included in 

Appendix B. 

Environmental Considerations

There are significant environmental issues that must be addressed for this project. A cost

factor in laying cables is its burying in the seabed, an exercise that also has an environmental 

impact. The cable prices provided by the cable manufacturers reflects the burying of cables 

where needed based on the seabed information provided in the request for information. One 

cable manufacturer based cost for laying the cable on the assumption that the cable would be 

buried for depths less than 125 meters. When the cables are to be purchased, the depth 

requirement will need to be specified to ensure that its environmental impact is acceptable.

Reliability Considerations

The main components of cable transmission are subject to failure, so that when a failure does 

occur usually results in loss of delivered energy. It is not possible to predict future failure of 

equipment for the OWITS Project. All we can do in this respect is assign a failure rate and 

repair time to the equipment that meets our expectation for cable operation. Variations to the 

selected failure rates and repair times can be made to evaluate sensitivity of the energy 

delivery to cable transmission outage. However, the depth to which cables are buried in the 

seabed and the separation distance between them will impact the reliability of the cable 

system. The cable contractor can recommend suitable burial strategies to optimize cable 
- 18 -

laying costs against improvements in expected reliability, but would do so after they have 

conducted a thorough seabed survey. 

The loss of energy delivered (usually designated loss of load expectation or LOLE) for each 

of the preferred options is estimated in Appendix A. This analysis concluded that the cost of 

spare cables for all DC Options could not be justified from savings in replacement energy that 

was possible following cable failure.

The one converter station equipment supplier that has a significant number of VSC 

transmission systems in service so that a performance record is available, provided the 

following expected outage statistics that would apply to one 200-MW pole or monopole. 

Undersea cable outages are excluded from these values.

Forced Outage rate (FOR) <5 outages/year 

Forced Energy Unavailability (FEU) <0.5% 

Energy unavailability due to scheduled maintenance (SEU) <1.0% 

Forced outages in the converter stations are usually of a short duration and are usually due to 

control and protection issues and operator error.

Loss Considerations

The cost of losses for the DC and AC Cable options was determined in Appendix A. A 

capitalized value of the cost of losses was estimated for each Option and for addition to the 

capital costs of the cables and terminal stations. Variations in the capitalized cost of lost 

energy do not change the selection of preferred Cable options. 

Future Connection to Maui

A Stage 2 interconnection from Maui to the transmission system constructed in Stage 1 is 

contemplated as a consideration for expansion capabilities of the Stage 1 configurations as 

indicated in Figures 3 to 9. Definition of the project and the installation date for Stage 2 is not 

known. The objective of evaluating these options is to determine potential benefits of 

constructing Stages 1 and 2 simultaneously. 
- 19 -

Capital Costs Assessment

Requests of information and costs were requested of the suppliers of VSC converter stations 

and undersea cables for the six DC options and the one AC option for the Oahu Wind 

Integration and Transmission Study. A copy of the documents requesting the information 

from the suppliers is included in Appendix D. 

Accuracy of Costs Provided

The accuracy of the costs provided for the VSC converter stations where stated by the DC 

equipment suppliers in their responses as being ±20% but the variation of costs between the 

three equipment suppliers was 1.5:1. The accuracy of capital costs provided for the supply 

and laying of the undersea cables where stated was also at ±20%, but the variation of budget 

costs was 3:1. These variations in budget costs raise uncertainty to the values used. However, 

the lowest costs were provided by a supplier who has constructed operating VSC projects. 

Consequently, the budget costs used herein are expected to not be too far from reality. 

Detailed seabed information, metal prices and currency exchange rates will impact the final 

costs.

Range of Costs for Terminating Substations

The responses received for the DC Options are summarized in Table 1 were the costs for the 

Stage 1 development of the Inter-Island DC cable transmission options. Stage 2 costs from 

Maui to Oahu are included as derived from Stage 1 costs and are approximate at this stage. 

These costs are based on a 20% addition to the lowest cost provided in order to arrive at an 

estimate that is not underpriced and to allow for variations in seabed information, metal 

prices and currency exchange rates. The identities of the suppliers are excluded to maintain 

confidentiality. 
- 20 -

Table 1: Capital Costs in 2009 millions of dollars as provided by suppliers of DC cable and 

DC converter equipment for the DC Options (with ac cable between Molokai and 

Lanai A1-2 (b)). 

Option C3-2 A3-2 A1-2 B3-2 C1-2 B1-2

Description 400 MW 

Koolau 

to 

Molokai 

200 MW 

Molokai to 

Koolau, 200

MW Molokai 

to Iwilei

200 MW 

Molokai to 

Koolau, 200MW 

Lanai to Iwilei, 

200 MW Lanai 

to Molokai

400 MW 

Molokai 

to Iwilei 

200MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau

200MW 

Molokai to 

Iwilei, 200 

MW Lanai 

to Iwilei

(a) (b)

Stations $M 234 288 414 342 234 288 288

Cables $M 154 180 367 424 221 216 245

Total Stage 

1 Price $M

388 468 781 766 455 504 533

Stage 2 

Maui to 

Oahu 

(Approx)

Converter 

Stations $M

144 144 117 117 144 144 144

DC Cables 

$M

420 420 192 192 283 272 272

Total Stage 

2 Price $M

564 564 309 309 427 416 416

Total Stages 

1 & 2 $M

951 1,032 1,090 1,077 882 920 949

These prices are the value for engineering, procurement and construction (EPC). They 

exclude costs to the purchaser in terms of insurance, site preparation, connection costs to the 

grid or wind farm collector system, purchaser’s management and engineering costs and 

interest during construction. 

The Stage 2 prices would be adjusted for escalation and present value that would depend on 

the number of years the installation would follow Stage 1. 

Costs for DC Converter Station Options

The prices received from the three major suppliers of DC converter stations are estimated into 

a useable value in Table 2. There is variation in prices received and the values estimated for 

inclusion in the summary are included in Table 2. The estimated cost applied is 20% higher 

than the lowest price submitted.
- 21 -

Table 2: Prices for DC converters, single end 

Type of DC Converter Station Estimated Price $M

200-MW symmetrical monopole DC converter station 72

400-MW bipole DC converter station 117

200-MW pole of a 400-MW DC converter station built first 63

200-MW pole of a 400-MW DC converter station built second at a 

different time 

54

Capital Cost Evaluation of Cable Options

The prices for DC cable options are summarized in Table 3. From these prices, the capital 

costs are assembled into Table 1. It was disclosed by several cable manufacturers that AC 

cable circuits as requested for AC Option A1-1 (Figure 9) were not practical and no pricing 

was provided. One stated that AC Option A1-1 is “deemed impractical for transmission due 

to distance, depth, losses, charging current, operational difficulties, cost, time for transport 

and cable laying. Depth would require spaced 3 x single-core cables for laying, three passes 

with cable laying vessel. More conductor area would be provided in armor due to increased 

current induction compared to three core cables.”

Another cable manufacturer responded that “the water depths between Lanai, Molokai and 

Oahu preclude using 3-core cables due to their greater weight. Single-core cables require 

greater conductor area in the cable armor to handle the higher induced currents. Cable 

charging current (of single core cables) would be in the order of 420 amps per 50 km of cable 

requiring greater conductor area for these longer cable distances. The installed cost for the 

longer, deep water AC cable crossing would be significantly higher. Furthermore, the remote 

wind plants would be exposed to system faults on Oahu leading to overall performance 

issues. Therefore, using AC submarine cables for these circuits is deemed impractical. Hence 

no budgetary estimates are provided for the AC cable option. On the other hand, use of 3-core 

AC cables for interconnecting Molokai with Lanai with the shallower water depths and 

shorter distance, especially if some overhead transmission could be used, is practical, 

economic, provides for greater resource diversity and operating flexibility.” 

The prices for DC cables in Table 3 are basically for both a 400-MW bipole where 1200 mm2

conductor was priced and for a 200-MW symmetrical monopole where a 500 mm2 conductor 

was priced. (Note that in the technical studies for the bipole configuration, a 1600 mm2 DC 

cable was applied. This difference will have minimal impact on the results of the technical 
- 22 -

study since the conclusions on the technical performance will not change because of the cable 

conductor size). However, prices of the DC undersea cables will vary with conductor size and 

the cable suppliers selected the sizes to apply in their response to the price request. Again the 

estimated cost applied is 20% higher than the low price submitted. 

Table 3: Prices for DC cables including burial and terminations as provided by suppliers of 

undersea cables

DC Cable Configuration Estimated Price 

$M

400-MW bipole: 3 cables 60 km, 2 at ±150 kV, 1,333 A, 1 at 1,333 A, 50 kV 154

400-MW bipole: 3 cables 87 km, 2 at ±150 kV, 1,333 A, 1 at 1,333 A, 50 kV 221

2 to 200-MW monopoles: 2 cables 60 km, 2 Cables 87 km, ±150 kV, 667 A 180

2 to 200-MW monopoles: 2 cables 60 km, 2 Cables 64 km, ±150 kV, 667 A 3 

cables 126 km for 400-MW bipole operation

367

2 to 200-MW monopoles: 2 cables 60 km, ±150 kV and 667 A, 2 cables 120 km, 

667 A

216

2 to 200MW monopoles: 2 cables 87 km at ±150 kV and 667 A, 2 cables 126 km, 

667 A

245

The cases prepared and studied route undersea cable around Molokai outside the southern and 

western reef in preference to overhead transmission across Molokai. It is recognized that 

capital costs will be minimized with minimum undersea cable length. This option can be 

studied further if an overland route across Molokai is considered to be a viable alternative and 

it is acceptable to take the undersea cable through the reef to an on-shore location on the 

south side of Molokai. 

Consideration for 400 MW Wind Generation on Lanai

The options selected for HVDC cables from Lanai and Molokai as presented in Figures 3 to 8 

are based on the assessment reported in Appendix A. Options C3-2, A3-2 and B3-2 have 400 

MW of wind generation only on Molokai and none on Lanai. These were selected simply 

because they were lowest cost resulting from Molokai being closer to the Oahu load than 

Lanai. 400 MW of wind generation on Lanai was evaluated in the option selection process 

reported in Appendix A as Options C2-2, A2-2 and B2-2. With the update from supplier’s 

capital costs for undersea cables, the comparison between options with 400 MW of wind 

generation on Molokai and on Lanai for Stage 1 capital costs is presented in Table 4. 
- 23 -

Table 4: Stage 1 Capital Costs in 2009 millions of dollars as provided by suppliers of DC 

cable and DC converter equipment for the DC Options that include 400 MW of wind 

generation on Lanai compared with on Molokai 

Option C3-2 C2-2 A3-2 A2-2 B3-2 B2-2

Description 400 MW 

Molokai to 

Koolau 

400 MW 

Lanai to 

Koolau, 

200 MW 

Molokai to 

Koolau, 200

MW Molokai

to Iwilei

200 MW 

Lanai to 

Koolau, 200

MW Lanai

to Iwilei 

400 MW 

Molokai to 

Iwilei

400 MW 

Lanai to 

Iwilei

Stations $M 234 234 288 288 234 234

Cables $M 154 318 180 303 221 303

Total Stage 1 

Price $M

388 552 468 591 455 537

Impact of Losses

The cost of losses between Options was evaluated in Appendix A where the assumptions for 

their analysis are presented. One key assumption was that the cost of losses was assessed at 

15c/kWhr for a load capacity factor on the cables derived from the wind energy sources at 

35% and at 25c/kWhr for a load capacity factor of 25%. 

The loss accumulation for the Stage 1 development of cable transmission from Lanai and 

Molokai is assumed over 20 years and the present value of these losses is capitalized to year 

1. The discount rate is applied at 5% p.a3

. The capitalized value of losses is then added to the 

capital cost of the Stage 1 option and is summarized in Table 5 for a 35% capacity factor and 

in Table 6 for a 25% capacity factor. 

The assumptions of cost of make-up power for losses, 20 years for a present value analysis, 

5% for discount rate and 25% and 35% for capacity factor offer a general indication of the 

impact of the cost of losses for comparison with capital expenditure. The values applied for 

these assumptions cannot be accurately predicted since they entail knowing the future. For 

example, 20 years for present value analysis might be too short, but the life of wind turbine 

generators is about 20 years, but the undersea cable may last over 40 years. In this case, 20 

years for present value analysis is selected. Similarly, a discount rate of 5% is applied, but in 

this day and age the difference between escalation and interest may be quite different and 

change over time. If Stage 2 to Maui is developed, then capacity factor on the cables may 

 

3 Discount rate as applied here is approximately the difference been long term interest and escalation of costs.
- 24 -

increase above 35%. Therefore, the cost of losses, reliability and life cycle costs are 

represented in this study as an indication of their impact and not a definite measure.

Impact of Reliability

The main components of cable transmission are subject to failure, so that when a failure does 

occur it usually results in loss of delivered energy. It is not possible to predict future failure of 

equipment for the OWITS Project. All we can do in this respect is assign a failure rate and 

repair time to the equipment that meets our expectation for cable operation. Variations to the 

selected failure rates and repair times can be made to evaluate sensitivity of the loss of energy 

delivered due to cable transmission outage.

The basic unscheduled failure rates and repair times are listed in Table A-3 of Appendix A. 

They are indicative of what may be expected of the undersea cable performance. The loss of 

energy delivered (usually designated loss of load expectation or LOLE) for each of the 

preferred options is assembled into Tables 5 and 6. This LOLE energy is costed both at 

15c/kwh (35% capacity factor) in Table 5 and at 25c/kwh (25% capacity factor) in Table 6 for 

a 20 year present value accumulation at a discount rate of 5% similar to the loss evaluation.

Risk

The reliability analysis undertaken in Appendix A and with results included in Tables 5 and 6 

is operational risk equated into a cost for comparison purposes. The risk associated with 

implementing the equipment and relatively new technology of voltage sourced HVDC 

converters and solid insulated HVDC cables cannot be readily translated into comparative 

costs. The main assurances on implementation risk are:

1. Voltage sourced converters are a successful technology that can be used with low cost 

undersea cables.

2. The first application of applying voltage sourced converters for a dedicated radial 

HVDC feeder came into service as the BorWin Alpha project and was commissioned 

towards the end of 2009. This is a 400-MW offshore wind farm HVDC feeder in the 

North Sea where the sending end converter station is on a platform as shown in Figure 

10. The assurance here is that the VSC converter can provide an adequate AC voltage 

for wind turbine generators to operate into. Conventional HVDC transmission 

technology cannot do this unless there is AC short circuit capacity provided by 

synchronous generators or condensers that will support AC voltage for both the wind 

turbine generators and the conventional HVDC converters. Voltage sourced converter 
- 25 -

technology has become acceptable in the electric utility industry. Performance of the 

Cross Sound VSC Cable and VSC Converters (commissioned in 2002) indicate its 

performance to be within the normal range of operation of HVDC transmission.4

Figure 10: BorWin Alpha Project 

(Photos courtesy of ABB) 

The greatest implementation risk in this project will be to have effective project management

with the purchaser and with the supplier. Having technical expertise of the equipment 

supplier who can be committed to support the project is also key. This is a challenge for 

equipment suppliers who are spread thin with other large projects. If project management and 

high level technical support is inadequate, the project will suffer delays in installation and in 

achieving acceptable operational performance. 

Life Cycle Costs

Life cycle cost considerations for HVDC substation and transmission components and 

equipment include all of the possible costs. Those costs include operation and maintenance

(O & M), labor, spare parts, expected repairs, insurance and warranties that a piece of 

 

4 Report to 11th FACTS User’s Group, October 22-24, 2008, Islandia, NY by CrossiSound Cable Company, 

LLC 
- 26 -

equipment would normally be expected to encounter during its service life. Life cycle cost 

should also include some expected outage costs for planned and unplanned maintenance. 

Local and State annual taxes and grants can be included in the life cycle costs. The life cycle 

costs of a DC-cable transmission system and wind generation from Molokai or Lanai can also 

include operating costs saved on Oahu fossil fuel generators when displaced by renewable 

energy. 

Excluding taxes and savings in operating costs due to use of wind generation compared to 

fossil fuel generators, a percentage of capital station cost at 1% pa is selected for basic 

operation and maintenance (O & M) and other operating charges over a 20-year life cycle for 

a present value (PV) assessment at a 5% discount rate. Operating costs due to losses and 

reliability in both the cables and the converter stations are discussed above and are separately 

included in Tables 5 and 6. The planned maintenance outage of 1 week per two years is 

included as part of the operating cost and assigned the same values for energy not delivered 

as for losses and reliability. 

Table 5: 20 year present value cost of losses, impact of reliability and life cycle costs for the 

selected DC undersea cable Stage 1 transmission options for a 35% capacity factor. 

Option C3-2 A3-2 A1-2 B3-2 C1-2 B1-2

Description 400 MW 

Koolau to 

Molokai 

200 MW 

Molokai to 

Koolau, 200

MW Molokai 

to Iwilei

200 MW 

Molokai to 

Koolau, 200

MW Lanai to 

Iwilei, 200 MW 

Lanai to 

Molokai

400 MW 

Molokai 

to Iwilei 

200 MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau

200 MW 

Molokai to 

Iwilei, 200 

MW Lanai 

to Iwilei

Total Stage 1 

Price $M

388 468 781 455 504 533

PV Losses

$M

122 129 137 124 133 135

PV (LOLE) 

Reliability $M

41 60 73 47 83 79

PV Life cycle 

costs $M

40 42 59 40 59 59

Total PV 

Operating 

Costs $M

203 231 269 211 275 273

Total Stage 1 

PV costs $M

591 699 1,050 666 779 806
- 27 -

Table 6: 20 year present value cost of losses, impact of reliability and life cycle costs for the 

selected DC undersea cable Stage 1 transmission options for a 25% capacity factor.

Option C3-2 A3-2 A1-2 B3-2 C1-2 B1-2

Description 400 MW 

Koolau to 

Molokai 

200 MW 

Molokai to 

Koolau, 200

MW Molokai 

to Iwilei

200 MW 

Molokai to 

Koolau, 200

MW Lanai to 

Iwilei, 200 MW 

Lanai to 

Molokai

400 MW 

Molokai 

to Iwilei 

200 MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau

200 MW 

Molokai to 

Iwilei, 200 

MW Lanai 

to Iwilei

Total Stage 1 

Price $M

388 468 781 455 504 533

PV Losses

$M

192 201 209 194 205 208

PV (LOLE) 

Reliability $M

48 72 87 55 98 95

PV Life cycle 

costs $M

42 42 62 42 62 62

Total PV 

Operating 

Costs $M

282 315 358 291 365 365

Total Stage 1 

PV costs $M

670 783 1,139 746 869 898

The higher present value operating costs of Table 6 with lower 25% capacity factor for the 

wind generation compared to the operating costs in Table 5 with its 35% capacity factor is 

due to the higher cost charged for make-up energy for the lower capacity factor. This is 

15c/kwh for 35% capacity factor in Table 5 and at 25c/kwh for 25% capacity factor in Table 

6. 

Due to the assumptions made for establishing losses, reliability and operating costs for the dc 

cables and converter stations (Appendix A), the values presented for total present value 

operating cost in Tables 5 and 6 are useful as a guide only. The results do indicate however 

that operating costs can be significant. 

Independent Option

An independent option was offered by one of the HVDC equipment suppliers as shown in 

Figure 11. No configuration for Stage 2 was provided. 
- 28 -

Figure 11: Independent HVDC Option

This option proposes thyristor-controlled resistors on the AC busbars at the wind farms on 

Molokai and Lanai. These are provided since loss of one pole of the bipolar HVDC feeder to 

Iwilei will cause the remaining operational pole to overload through the AC cable connection 

between Lanai and Molokai. Wind farm power under heavy wind conditions still maintains 

its level of generation until tripped or reduced generation of wind power. With one pole to 

Iwilei out of service, this power will initially pass through the remaining pole causing it to 

overload. The thyristor-controlled resistors are designed to absorb access power temporarily 

until the excess wind generation can be safely removed off-line. 

The Stage 2 development might best be applied as a single symmetrical monopole or with a 

three core AC cable from Maui to Lanai if the seabed depth is shallow enough. Power 

transfers with Oahu could be applied through the bipole from Lanai and Molokai to Iwilei 

from the interconnection at Lanai. However, with just two HVDC poles into Iwilei, the 

overall bipole rating should not be increased where loss of a pole exceeds the single 

contingency limit, at present established at 200 MW. 

The major contribution of the Independent HVDC Option is the termination at Lanai of the 

Stage 2 cable transmission circuit from Maui. There is a significant savings in Stage 2 

undersea cable capital costs by not laying 70 miles of cable between Lanai and Iwilei

(approximately $178 million). This limits the power import into Oahu from Maui to the 

capacity of the Stage 1 transmission minus the power being generated by the wind farms. 

With a wind farm capacity factor of 35%, there will be significant times when power can be 

200 MW

200 MW 

Iwilei 

400 MW Total 

Maui

Molokai

200 MW Pole – Stage 1

200 MW Pole – Stage 1

Lanai

Stage 2 - Undefined 

Thyristor Controlled Resistor 

Thyristor Controlled 

Resistor

AC Cable
- 29 -

imported directly into Oahu from Maui. This will increase the capacity factor on the Stage 1

cable transmission to Oahu, thereby increasing its cost effectiveness. 

There will be no restriction for when power can be imported into Maui from the wind farms 

on Lanai and Molokai or directly from Oahu. A capacity limitation will be set by the ability 

of the electric power system on Maui to survive a single contingency loss. For this analysis, a 

200-MW limit was applied, but additional study is required to determine what the Maui 

single contingency loss level is. When known, the initial rating of the cable transmission out 

of Maui can be determined. 

To compare what impact terminating the Stage 2 cable transmission from Maui at Lanai 

instead of Oahu, options B1-2 and C1-2 are selected. These two options have a 200-MW 

Stage 1 symmetrical monopole on Lanai. Stage 2 from Maui is terminated at Lanai as shown 

in Figure 12. No cable transmission is applied between Lanai and Molokai for this 

assessment.

1. Revised Option B1-2 (b) Revised Option C1-2 

Figure 12: Terminating Stage 2 cable transmission at Lanai instead of Iwilei

 The capital costs of the Independent HVDC Option compared with selected Options B1-2 

and C1-2 when the Stage 2 cable transmission is terminated at Lanai instead of at Iwilei is 

presented in Table 7. 

200 MW

Iwilei 

400 MW Total 

Maui

Molokai 

200 MW Stage 2 

200 MW Symmetrical 

Monopole – Stage 1 

Lanai 200 MW Symmetrical 200 MW Monopole – Stage 1 

Molokai 

2 - 200 MW Symmetrical 

Monopoles – Stage 1 

200 MW

Koolau

Maui

200 MW Stage 2

Lanai 200 MW 
- 30 -

Table 7: Capital costs for the Independent HVDC Option compared with Options B1-2 and 

C1-2 

Option Independent B1-2 B1-2-

Revised

C1-2 C1-2-Revised

Description 200 MW 

Molokai to 

Iwilei, 200 

MW Lanai to 

Iwilei, Stage 

2 MW Maui 

to Lanai

200 MW 

Molokai to 

Iwilei, 200 

MW Lanai to 

Iwilei, Stage 

2 Maui to 

Iwilei

200 MW 

Molokai to 

Iwilei, 200 

MW Lanai to 

Iwilei, Stage 

2 Maui to 

Lanai

200 MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau, 

Stage 2 Maui 

to Iwilei

200 MW 

Molokai to 

Koolau, 200 

MW Lanai to 

Koolau, Stage

2 Maui to 

Lanai

Stations 

$M

261 288 288 288 288

Cables $M 424 245 245 216 216

Total Stage 

1 Price $M

685 533 533 504 504

Stage 2 

Maui to 

Oahu 

(Approx)

Converter 

Stations 

$M

144 144 144 144 144

DC Cables 

$M

94 272 94 272 94

Total Stage 

2 Price $M

238 416 238 416 238

Total 

Stages 1 & 

2 $M

923 949 771 920 742

If the termination of Stage 2 at Lanai and/or Molokai is acceptable, then the significant 

savings in capital costs can be achieved as the results in Table 7 indicate. Further savings in 

capital costs and converter station losses will be achieved if the Stage 2 HVDC cable 

transmission is connected in multi-terminal transmission from Maui to Lanai to Oahu. Further 

work is needed to investigate the options for terminating the Stage 2 cable transmission from 

Oahu at Lanai, to include impacts of losses, risk, and technical requirements. 

Technical Study 

The study for this project is based on a technical analysis of the six previously identified DC 

Cable transmission options and routes for a transmission expansion with interconnections 

between four of the State of Hawaii’s Islands, consisting of Lanai, Oahu, Maui, and Molokai. 

The six options are presented in Figures 3 to 8 and the details and selected results of the 
- 31 -

Technical Study are in Appendix C. The technical study was undertaken for the Stage 1 DC 

Options only as represented in Figures 3 to 8. 

Objectives

The scope of this effort is to extend the body of work currently developed by the OWITS 

project teams [1], [2] and further evaluate the suitability and feasibility of the preferred 

options determined in Appendix A. Assessment is made of the recommended technology of 

HVDC Voltage Sourced Converters (VSC) cable transmission to connect between Oahu, 

Lanai and Molokai and Maui, although additional work is being conducted to refine this 

analysis. The study considers a means to safely operate wind farms on the Molokai, Lanai 

and Maui through VSC feeders. When more information is known on the Stage 2 

interconnection to Maui including its power system, further work will be required to develop 

the cable transmission that would apply. 

Study Considerations

Potential issues with the connection of the wind plant and the VSC cable transmission system 

are studied assuming wind turbines are designed with state-of-the-art controls. This analysis 

is performed for two different types of wind turbine systems using DFIG and Full Converter 

generic models. This work is undertaken with PSCAD5 that uses a network model translated 

directly from a PSS/E6 case by E-TRAN7

, using both the solved power flow (.raw) and 

dynamics (.dyr) files. The VSC converter models are also generic but reflect the system 

control technologies applied by the two main suppliers of this equipment, ABB and Siemens. 

The assembled wind turbine and dc link models will respond dynamically in PSCAD and 

include the effect of control interactions and their damping, both at small signal and large 

non-linear signal levels.

VSC Converter Control Strategy

The controls for each pole or symmetrical monopole are separate and independent from any 

other pole or monopole. This is so each pole of 200 MW is the largest outage that a single 

component failure can produce. 

 

5 PSCAD is an electromagnetic transients program licensed by Manitoba Hydro 6 PSS/E is a power flow and transient stability simulation program from Siemens PTI

7

 E-TRAN is a program to translate network data from PSS/E to PSCAD
- 32 -

There are a number of options for configuring the controls of the VSC converters at the wind 

farm end. What proved to be most effective was to lock the valve firing oscillator to generate 

60-Hz alternating voltage and control the AC voltage at the sending end system. This strategy 

provides the necessary effective short circuit capacity to allow connection of most types of 

wind turbine generators to the wind farm. This frequency controlling strategy can be 

expanded to mirror the HECO system frequency at the wind farms on Molokai and Lanai. 

The benefit in doing this is that if inertia producing wind turbine generators are installed to 

help in the operation of the HECO grid system, then any modulated power so generated at the 

wind farms will automatically transfer through the VSC cable transmission into the HECO 

system. 

The VSC converter connected at the receiving end to the HECO grid controls the DC voltage 

applied to the DC cables. This VSC converter can also provide support to the HECO AC 

system through several different modes of control selected by the Operator. These are: 

1. Reactive Power Control. This will be useful where the AC voltage at the 138-kV 

interconnection busbars is controlled by the installed HECO facilities such as nearby 

generators and switched capacitor banks. With the DC converter in a constant reactive 

power control mode, there is less possibility for voltage control interaction between 

the DC converter and the nearby generators connected to the HECO system.

2. AC Voltage Control. The AC voltage on the converter station interconnection busbar 

can be controlled by the voltage sourced converter(s) similar to a STATCOM. A 

suitable adjustable droop characteristic will be needed to ensure the voltage control 

coordinates with the existing or other voltage controlling facilities. The speed of the 

AC voltage controller of the converter will need to be designed to coordinate with the 

other voltage controlling facilities as well. Voltage control on the Oahu end would be 

desirable for the HECO system. Especially on the east end where there aren’t any 

“nearby generators” at times. This is one of the benefits assumed from the HVDC

system to mitigate voltage issues following contingency events on the Oahu system. 

3. Power Factor Control. Such a controller is possible and may be desirable to have if the 

interconnection agreement specifies a power factor range of operation. 
- 33 -

These modes of control can be specified to be delivered with the converters and be set by the 

System Operator through a SCADA or other remote or local communication link. 

Most Severe Single Contingency Disturbance

The most severe single contingency disturbance is an AC bus fault at the terminating 

interconnection busbar of the DC cable transmission, with delayed clearing which results in a 

200-MW pole or monopole being disconnected as shown in Figure 13. 

Figure 13: Receiving end fault leaving DC cable open ended at its receiving end

With the fault shown in Figure 13, the power from the wind turbine will continue flowing 

into the cable through the converter at the sending (wind farm) end, causing the voltage on 

the DC cable to rise. Protection against overvoltage on the DC cable is achieved by a 

supplementary DC chopper circuit as shown in Figure 13. The DC chopper is a resistor that is 

switched in and out across the receiving end of the cable with a solid state switch.

With a bus fault at one of the terminating busbars of Iwilei or Koolau that trips a 200-MW 

DC Cable feeder from Molokai or Lanai, the following occurs: 

1. The DC voltage on the cable of the tripped pole is contained by the DC chopper 

2. The HECO grid system on Oahu is deprived of the 200 MW and should recover as 

determined by system studies [2]. 

3. If the 200 MW DC pole that trips out of service is the only feeder to the HECO grid 

from the wind farm, then all the wind turbine generator units in the wind farm must be 

transfer tripped out of service. If the DC pole that trips out of service is just one pole 

of either a bipole or two monopoles from a 400-MW wind farm (such as DC Options 

C3-2 Figure 3, A3-2 Figure 4, A1-2 Figure 5 or B3-2 Figure 6), then the remaining 

pole is subject to overload. This overload will be twice its rating if the wind is 

Circuit breaker opens 

to clear fault

Sending End DC Chopper

Fault

Receiving End

Circuit breaker opens on 

transfer trip from 

receiving end breaker
- 34 -

operating at its maximum capacity of 400 MW. Consequently a protection has to be 

designed into the DC Cable system which might be one of: 

• Purchase the VSC converters and undersea cables with enough emergency 

rating to accommodate the overload 

• Require that the wind turbine generators have a power order controller that 

forces production power in the wind farm to a level that the remaining DC 

pole can transfer under emergency conditions

• Apply a transfer trip to enough operating wind turbine generators to bring the 

production power of the wind farm to a level the remaining DC pole can 

transfer.

Impact of Faults on Oahu on the Wind Turbine Generators

VSC cable transmission provides a buffer to AC system faults at one end significantly 

impacting the AC system at the other end. The receiving end AC system faults may cause the 

DC cable voltage to increase, but this is managed by the DC chopper. Consequently because 

the AC voltage and frequency that the wind farms on Molokai and Lanai are connected to 

stay relatively steady, the impact to the wind turbine generators on both islands is minimal for 

a severe AC fault on the HECO grid system on Oahu. 

Impact of AC Faults on Molokai or Lanai on the HECO Grid on Oahu

The consequence of severe AC system faults at Molokai or Lanai on the HECO grid on Oahu 

is also minimal due to the buffering properties of the VSC cable transmission. If the fault at a 

wind farm clears without losing the HVDC link or a significant loss of wind turbine 

generators, the impact at the receiving end will not be significant. If the HVDC system or a 

large number of wind turbines trip because of the disturbance, then the loss of generation will 

reflect through to the HECO grid system which will have to adjust accordingly. 

During the studies of this disturbance, a control interaction in the form of 60-Hz oscillation 

was observed. The interaction occurred with DC Option A3-2 (Figure 4) following the 

clearing of an AC fault on the 33-kV bus of the Molokai wind farm. The two symmetrical 

monopoles were interacting at their sending end with involvement from the DFIG wind 

turbine generators. The FC wind turbine generators appeared to not be involved in the 

interaction.
- 35 -

Connection to Local Load on Molokai or Lanai

A review of the results to disturbances for the various options for DC cable transmission 

indicate that a steady AC voltage and frequency for the sending end wind farms on Molokai 

or Lanai is achieved so long as the DC converters remain in operation. This still holds when 

there is no wind. The VSC cable transmission will feedback power to the wind farms from 

the HECO grid to maintain the wind turbines in hot standby. 

Under these conditions, there is a potential to directly connect from the AC collector system 

of the wind farms to the local load through a conventional AC substation as shown in Figure 

14. However, further more detailed analysis is needed to determine the interconnection 

requirements, such as the protection requirements, for this option. At a minimum, a transfer 

trip to the interconnection to the local load will be required when the last VSC transmission 

pole is taken or forced out of service because the sending end AC voltage and frequency can 

no longer be maintained. This is a consequence of when the DC cable transmission is forced 

out of service and the wind farm must be transfer tripped for the same reason. 

If it is anticipated that this interconnection to local load is to be the only source of operating 

generation to the local load, then a standby power supply will be required for when the 

HVDC link is down. It is not usual for HVDC transmission be the sole source of generation 

for a utility grid but it has been applied to provide supply to off-shore oil and gas pumping 

stations. From a capacity planning standpoint, one way to consider the interconnection to 

local load is as if it is another generator. It is subject to forced and scheduled outages of the 

DC cable transmission. If two poles or monopoles are connected to the wind farm as with DC 

Options C3-2 Figure 3, A3-2 Figure 4, A1-2 Figure 5 or B3-2 Figure 6, then the reliability of 

supply to local load will be significantly increased. Under such circumstances the 

interconnection from the wind farm may be considered as the only source of generation to 

local load, if the other technical interconnection issues are analyzed and addressed. 
- 36 -

Figure 14: Interconnection to local load 

Conclusions 

From this study, the following conclusions can be drawn: 

1. An AC cable option is only viable if three core XLPE cable can be applied, but which 

is limited by the depth to which it can be laid because of its weight. Consequently it 

cannot be considered for a connection between Lanai or Molokai into Oahu. However, 

it could be used to interconnect Molokai and Lanai and Maui. 

2. Capital costs for the six VSC converter station and DC cable options have been 

provided by cable and HVDC equipment suppliers. There was considerable variation 

in the capital costs received. The lowest cost option for a Stage 1 development of 400 

MW of wind energy was Option C3-2 (Figure 3) with wind energy developed only on 

Molokai. This is because the undersea cables are the shortest and therefore the lowest 

cost. 

3. If the Stage 2 cable transmission from Maui can be terminated at Lanai and/or 

Molokai instead of Oahu, then significant savings in Stage 2 costs can be achieved. 

This will reduce the power transfer capability from Maui into Oahu when the wind 

turbine generators on Lanai are generating. There will be less restriction in power 

transfer capability from Oahu to Maui due to back-feed against the normal flow into 

Oahu. 

Sending End VSC Converter

Wind Farm

Local Load

Interconnection 

Substation to Local Load
- 37 -

4. Voltage sourced converters are the only practical converters to apply with the DC 

cables. This is because they can create a stable AC supply for wind turbine generators 

to connect into. They also offer a significant buffer to AC system faults at one end 

adversely impacting the AC system at the other end. The wind turbine generators on 

Molokai and Lanai will not be affected significantly by severe AC system faults on 

Oahu. 

5. Careful design is required for the DC cable and converters to ensure that when the 

DC cable transmission is tripped out of service at its receiving (Oahu) end, that DC 

cable overvoltage is prevented and the wind turbine generators that lose their path to 

the load are effectively and quickly removed from operation. 

6. With a suitable control strategy for the VSC transmission, it will be possible to 

maintain a steady AC voltage and frequency for the sending end wind farms. This 

means that a direct and conventional interconnection to the small local loads on 

Molokai or Lanai may be an option, but requires further careful design as this is not 

usual for HVDC transmission to be the sole source of generation for a utility grid. It is 

only when the DC cable transmission is completely taken out of service that the 

interconnection to local load would have to be transfer tripped. 

References

1. R.W. Beck, “Hawaii Inter-Island Cable Study”, Draft report to the Department of 

Energy, May 15, 2009. 

2. Electric Power Systems, Inc., “OWITS TRC Update”, PowerPoint Presentation , April 

16, 2005. 

3. J. Dorn, H. Huang, D. Retzman, Siemens “Novel Voltage-Sourced Converters for 

HVDC and FACTS Applications”, CIGRE 2007 Osaka Symposium, Paper 314. 

4. S. Hirano, J. Haraguchi, T. Mizuno, H. Niinobe, Y. Nagoya, “Development of +/-250 

kV Coaxially-Integrated Return Conductor Extruded Insulation Cable,” CIGRE 2007 

Osaka Symposium, Paper 316. 

5. G. Evenset, B. Ladegaard, of Nexans, Norway AS, “Deep Water Cable Solutions – 

Cable System Development and Installation”, Paper 501, CIGRE SC B4 2009 Bergen 

Colloquium. 

6. M. Marelli, A. Orini, G. Miramonti, G. Pozzati of Prysmian, Italy, “Challenges and 

Achievements for New HVDC Cable Connections”, Paper 502, CIGRE SC B4 2009 

Bergen Colloquium. 

7. ABB AB, “Technical Description of HVDC Light Technology”, 

http://search.abb.com/library/Download.aspx?DocumentID=1JNL100105-

122&LanguageCode=en&DocumentPartID=&Action=Launch&IncludeExternalPubli

cLimited=True 
- 38 -

List of Appendices

Appendix A: Selection of Preferred Options for the Inter-island 

Transmission

 

Appendix B: Evaluation of SVC Requirement for Inter-island AC 

Cable Option

Appendix C: Simulation Studies for Inter-island DC Cable Options

Appendix D: Request for Information from DC Converter and Cable 

Manufacturers
- 39 -

APPENDIX A

Selection of Preferred Options for the Inter-island Transmission

Updated May 2010

Introduction

Eighteen inter-island AC and DC transmission options have been prepared for reduction to 7 

cases for further study. There are a number of assumptions that the creation of these 18 cases 

have been based on, and a presented here for further scrutiny:

1. Oahu receiving points: 200 MW Iwilei and 200 MW Koolau, 

400 MW Iwilei or 400 MW Koolau 

2. Lanai and Molokai sending points: 200 MW Lanai and 200 MW Molokai, 

400 MW Lanai or 400 MW Molokai 

3. Maximum N-1 outage possible: 200 MW 

4. 5 years after Lanai and Molokai interconnections are in operation, a 200 MW 

interconnection from Maui to Oahu is put in place. This study assumed a 200 MW 

Stage 2 interconnection to Maui could be made, but this is to be reviewed before the 

Stage 2 options to Maui are finalized. 

5. When the Lanai and Molokai interconnections terminate at the one location, either 

Iwilei or Koolau, the Maui to Oahu termination is located at Iwilei when the 400 MW 

termination is at Koolau, and at Koolau when the 400 MW termination is at Iwilei. 

6. A practical rating for the AC cables is 230 kV, 250 MW maximum, 3 core XLPE 

cable. This is ideally suited for the AC options for this project. The reactive power 

charging requirement for this cable is about 4.8 MVAR per mile, which is manageable 

for these applications. 3 core cables of larger capacity have not been made available 

by cable suppliers largely because their size becomes challenging to transport and lay.

7. For the DC options, 150 kV cables are proposed, either as symmetrical monopoles 

rated at 200 MW or 400 MW bipole when possible, assuming the poles of the bipole 

are independent so that the N-1 outage remains at 200 MW. 

8. The 18 options are all radial feeds with no more than a 200 MW single contingency. 

To reduce the single contingency outage to 0 MW, the added cables and ratings 

needed are difficult to justify. 
- 40 -

The method of elimination and reduction to the preferred options undertook the following 

assessments:

1. Capital cost, including present value analysis of incorporating the Maui 

interconnection 5 years after the Lanai/Molokai interconnections are in-service

 

2. Simple loss analysis. The loss analysis would be based on say a 20 year operating 

period. 

3. Reliability Assessment. Outages for cables, transformers and converters were 

assumed as in Table A-3. It is not possible to predict future cable failures. A failure 

rate and repair time to the equipment is assigned that meets expectations for cable 

operation. Such an assessment is to determine what spares are required. 

Impact of Losses

The cost of losses are capitalized to a present value and added to the capital costs. The 

assumptions for the loss analysis are as follows:

1. The cost of losses is to be assessed at 15c

/kWhr for a load capacity factor on the 

cables from the wind energy sources at 35% and at 25c

/kWhr for a load capacity 

factor of 25%. 

 

2. For convenience of basic analysis, losses are divided into “fixed” and “variable”. 

Fixed losses, also known as no-load losses are voltage dependent and are considered 

to remain fixed or unchanged as long as the cable is energized. Variable losses are 

proportional to the square of the current or loading on the cable transmission. 

3. When no power is flowing through the cable transmission, it remains energized where 

fixed losses are present but variable losses are zero. 

4. Variable losses are dependent on the load capacity factor. For the purpose of this loss 

assessment, the load capacity factor for the cable transmission to Oahu from Lanai, 

Molokai and Maui is considered as a straight line characteristic as shown in Figure 1.
- 41 -

Figure A-1: Representation of the annual load capacity factor for variable loss 

analysis. Capacity factor is the shaded area as a percentage of the total area of full 

load for one year. 

5. VSC converter station fixed losses are assumed to be 0.75% of a converter station 

rating and variable losses are 0.45% of converter station rating. The DC cable is 

assumed to only have variable losses. The AC cable accumulates fixed losses due to 

circulating charging currents at no-load and losses in the dielectric, and variable losses 

that accumulate in the main conductor, the shield and armor. Use of cables with 

higher losses will impact cable option preference since losses play a significant role in 

overall present value costs.

6. The shunt compensating reactors at the ends of the AC cables are not switchable, and 

their fixed losses are based on an X/R ratio of 70. No SVC or dynamic compensation 

is applied for the AC cable options. 

7. The loss accumulation for the Stage 1 development of cable transmission from Lanai 

and Molokai is assumed over 20 years and the present value of these losses is 

capitalized to year 1. The discount rate is applied at 5% p.a. The loss evaluation for 

Stage 2 cable transmission from Maui to Oahu is assessed over years 6 to 20, and the 

present value is capitalized to year 1. The capitalized value of losses is then added to 

the capital cost of the option.

8. In general, the loss of any one element is limited to 200 MW. For those DC options 

where 400 MW is to be delivered to the one site on Oahu from Molokai or Lanai, then 

a bipolar option is considered. This requires the laying of three cables, where one 

cable serves as a metallic return path. Each pole is independent of the other, and the 

DC pole cables need not be laid together to avoid common mode failure. Under such a 

configuration, an outage will be limited to 200 MW. The bipolar 400 MW 

0 100%

1.0

Capacity 

Factor

Duration through the Year 

Per-unit Loading on the Cable Transmission
- 42 -

configuration is possible for most options studied. This means the DC cables at 150 

kV are rated for 1,333 amp rather than 667 amp.

Capital Cost Summary Including Losses

The capital cost summary of the eighteen options is presented in Table A-1 for the cost of 

losses at 15c/kWhr and 35% capacity factor. The cost summary is repeated in Table A-2 for 

the cost of losses at 25c/kWh and 25% capacity factor. 

Table A-1: Cost summary of options for the Oahu Wind Integration and Transmission Study 

for 15c/kWh cost of losses and 35% capacity factor.

Option AC 

or 

DC

Description $M Capital 

Cost 

$M Present 

Value Loss 

15c/kWh 

35% CF

$M 

Total 

A1-1 AC 200MW, Koolau - 200 MW, Lanai - 200 

MW, Molokai - 200 MW

880 311 1191

A1-2 DC “ “ “ “ 711 179 890

A2-1 AC Iwilei - 200MW, Koolau - 200 MW, Lanai -

400 MW

973 381 1354

A2-2 DC “ “ “ “ 809 186 995

A3-1 AC Iwilei - 200MW, Koolau - 200 MW, 

Molokai - 400 MW

787 270 1057

A3-2 DC “ “ “ “ 698 172 870

B1-1 AC Iwilei - 400MW, Lanai - 200 MW, Molokai 

- 200 MW

897 311 1208

B1-2 DC “ “ “ “ 770 187 957

B2-1 AC Iwilei - 400MW, Lanai - 400 MW 966 376 1342

B2-2 DC “ “ “ “ 823 181 1004

B3-1 AC Iwilei - 400MW, Molokai - 400 MW 831 295 1126

B3-2 DC “ “ “ “ 739 176 915

C1-1 AC Koolau - 400MW, Lanai - 200 MW, 

Molokai - 200 MW

892 323 1215

C1-2 DC “ “ “ “ 758 185 942

C2-1 AC Kailau - 400MW, Lanai - 400 MW 983 393 1376

C2-2 DC “ “ “ “ 835 182 1017

C3-1 AC Koolau - 400MW, Molokai - 400 MW 749 253 1002

C3-2 DC “ “ “ “ 688 173 861
- 43 -

Table A-2: Cost summary of options for the Oahu Wind Integration and Transmission Study 

for 25c

/kWh cost of losses and 25% capacity factor.

Option AC 

or 

DC

Description $M Capital 

Cost 

$M Present 

Value Loss 

25c/kWh 

25% CF

$M 

Total 

A1-1 AC 200MW, Koolau - 200 MW, Lanai - 200 

MW, Molokai - 200 MW

880 492 1372

A1-2 DC “ “ “ “ 711 276 987

A2-1 AC Iwilei - 200MW, Koolau - 200 MW, Lanai -

400 MW

973 605 1578

A2-2 DC “ “ “ “ 809 284 1093

A3-1 AC Iwilei - 200MW, Koolau - 200 MW, 

Molokai - 400 MW

787 426 1213

A3-2 DC “ “ “ “ 698 267 965

B1-1 AC Iwilei - 400MW, Lanai - 200 MW, Molokai 

- 200 MW

897 492 1389

B1-2 DC “ “ “ “ 770 284 1054

B2-1 AC Iwilei - 400MW, Lanai - 400 MW 966 599 1565

B2-2 DC “ “ “ “ 823 278 1101

B3-1 AC Iwilei - 400MW, Molokai - 400 MW 831 466 1297

B3-2 DC “ “ “ “ 739 272 1011

C1-1 AC Koolau - 400MW, Lanai - 200 MW, 

Molokai - 200 MW

892 511 1403

C1-2 DC “ “ “ “ 758 282 1040

C2-1 AC Kailau - 400MW, Lanai - 400 MW 983 623 1606

C2-2 DC “ “ “ “ 835 278 1113

C3-1 AC Koolau - 400MW, Molokai - 400 MW 749 398 1147

C3-2 DC “ “ “ “ 688 268 956

The consideration for losses does not change the lowest capitalized cost options identified in 

red in Tables A-1 and A-2. The variation of cost of losses from 15c/kWh to 25c/kWh does not 

change the five lowest cost options either. The cost of losses is impacted more significantly 

by the cost value placed on losses rather than by load capacity factor.

Description of Preferred Options

Six HVDC options and one AC option are proposed for further analysis and described as 

follows. The landing locations on the Oahu end of the cable are limited to two locations to 

simplify the analysis and should not be viewed as the only alternatives for landing sites on 

Oahu as several are being considered and evaluated in other studies. The results of this 

study are not significantly impacted by the details of the Oahu landing sites, at least to the 

extent that sites at or near Koolau in the north and at or near Iwilei in the south may be 

contemplated. 

Landing sites on Molokai and Maui are positioned to avoid breaching live reefs to the 

greatest extent possible. This adds length to the undersea cable connections between 

Molokai and Lanai for Stage 1 and to Maui for Stage 2. Further Environmental Impact 
- 44 -

Assessment may justify shorter distances for the undersea cables between Molokai, Lanai 

and Maui, but for this study the longer cable lengths and higher costs will apply.

Figure A-2: Option C3-2, $M718 Present Value Capital Cost. Stage 1 connection from 

Molokai to Koolau.

The Stage 1, 400 MW HVDC cable transmission between Molokai and Koolau is in ±150 kV 

bipole configuration, requiring three cables to be laid. The Stage 2, 200 MW HVDC cable 

transmission between Maui and Iwilei is a ±150 kV symmetrical monopole configuration, 

requiring two cables to be laid. 

Figure A-3: Option A3-2, $M728 Present Value Capital Cost. Stage 1 connection from 

Molokai to Koolau and Iwilei.

The Stage 1, with 2 - 200 MW HVDC cable transmission between Molokai and Oahu to 

Koolau and Iwilei is a ±150 kV symmetrical monopole configuration, requiring four cables to 

be laid. The Stage 2, 200 MW HVDC cable transmission between Maui and Iwilei is in ±150 

kV symmetrical monopole configuration, requiring two cables to be laid. 

200 MW 400 MW

200 MW

200 MW 

Iwilei Maui

Molokai

Koolau 

200 MW Symmetrical 

Monopole – Stage 2 

400 MW Bipole – Stage 1 

200 MW

Iwilei

200 MW Symmetrical Maui

Monopole – Stage 2 

400 MW

Molokai

Koolau

Stage 1

200 MW Symmetrical Monopole

200 MW Symmetrical Monopole 
- 45 -

Figure A-4: Option A1-2(a): $M827 Present Value Capital Cost – With DC cable between 

Lanai and Molokai 

Stage 1 has a 200 MW HVDC cable symmetrical monopole transmission between Molokai 

and Oahi to Koolau. From Lania to Iwilei on Oahu is a 150 kV pole, 200 MW configuration, 

with two cables, of which one is a metallic return cable. For Stage 2, a 200 MW HVDC cable 

transmission between Maui and Iwilei is the other pole at -150 kV, requiring two cables to be 

laid from Maui to Lanai, with one cable extending to Lanai.

Figure A-5: Option B3-2: $M770 Present Value Capital Cost. Stage 1 connection from 

Molokai to Iwilei

The Stage 1, 400 MW HVDC cable transmission between Molokai and Iwilei is a ±150 kV 

bipole configuration, requiring three cables to be laid. The Stage 2, 200 MW HVDC cable 

transmission between Maui and Koolau is a ±150 kV symmetrical monopole configuration, 

requiring two cables to be laid. 

400 MW

200 MW

Iwilei 

Maui 

Molokai

Koolau 

200 MW Symmetrical 

Monopole – Stage 2 

400 MW Bipole – Stage 1

200 MW

Iwilei 

Maui

200 MW Pole - Stage 2 

200 MW

Molokai 

Koolau

Stage 1 

200 MW Symmetrical Monopole

200 MW Pole

Lanai

200MW Symmetrical 

Monopole between Lanai 

and Molokai 
- 46 -

Figure A-6: Option C1-2: $M788 Present Value Capital Cost. Stage 1 connection from 

Molokai and Iwilei to Koolau

Stage 1, consists of 200 MW, ±150 kV HVDC symmetrical monopole cable transmission 

between Molokai and Koolau and also between Lanai and Koolau, each requiring two cables 

to be laid. For Stage 2, a 200 MW HVDC ±150 kV HVDC symmetrical monopole cable 

transmission between Maui and Iwilei requires two cables to be laid.

Figure A-7: Option B1-2: $M800 Present Value Capital Cost (revised). Stage 1 connection 

from Molokai and Lanai to Iwilei 

Stage 1, consists of 200 MW, ±150 kV HVDC symmetrical monopole cable transmission 

between Molokai and Iwilei and also between Lanai and Iwilei, each requiring two cables to 

be laid. For Stage 2, a 200 MW HVDC ±150 kV HVDC symmetrical monopole cable 

transmission between Maui and Koolau requires two cables to be laid.

Maui

Molokai 

Lanai

200 MW Symmetrical 

Monopole – Stage 2 Iwilei

2 - 200 MW Symmetrical 

Monopoles – Stage 1 

200 MW 

200 MW 

200 MW 

Koolau 

200 MW 

200 MW

Iwilei 

600 MW Total 

Maui

Molokai

200 MW Symmetrical 

Monopole – Stage 2 

200 MW Symmetrical 

Monopole – Stage 1 

Lanai

200 MW Symmetrical 200 MW

Monopole – Stage 1 
- 47 -

Figure A-8: Option A1-1: $M917 Present Value Capital Cost. Stage 1 connection from 

Molokai to Koolau and from Lanai to Iwilei. 

Stage 1, consists of 200 MW, 230 kV AC 3 core XLPE cable transmission between Molokai 

and Koolau and also between Lanai and Iwilei, each requiring one 3 core cable to be laid. For 

Stage 2, a 200 MW, 230 kV AC 3 core cable transmission between Maui and Iwilei is 

required with a reactor station on Lanai. 

The preferred options with VSC converters on Molokai and Lanai for Stage 1 and on Maui for 

Stage 2 will tightly regulate AC system frequency on these islands to the extent that they can 

connect directly to local load through conventional AC substations.

The assumption that the Maui interconnection is rated at 200 MW has a large impact on 

Stage 2 costs. This requires an undersea cable rated to 200 MW for the full and lengthy 

distance from Maui to Oahu in order to be within the 200 MW N-1 restraint on Oahu. As a 

consequence, the cable options are all radial in order to maintain minimum costs.

Impact of Reliability 

The main components of cable transmission are subject to failure, so that when a failure does 

occur usually results in loss of delivered energy. It is not possible to predict future failure of 

equipment for the OWITS Project. All we can do in this respect is assign a failure rate and 

repair time to the equipment that meets our expectation for cable operation. Variations to the 

selected failure rates and repair times can be made to evaluate sensitivity of the energy 

delivery to cable transmission outage. 

The base unscheduled failure rates and repair times are proposed as listed in Table A-3. These 

values do not include usual increased failure rate that might be experienced during the first 

year of operation. They are only indicative of what may be expected of the undersea cable 

performance.

200 MW

200 MW

Maui

Molokai

Lanai

200 MW 

Iwilei 

Koolau 

Stage 2 – 230 kV AC 3 Core Cable

Stage 1- 230 kV AC 3 Core Cable

Stage 1 – 230 kV AC 3 Core Cable
- 48 -

Table A-3: Base failure rates and repair times for undersea cable transmission to Oahu

Equipment Failure Rate Repair Time Forced 

Outage Rate 

q 

Frequency of 

Outage λ

Transformer 1 outage/20 yr 2 weeks 0.001923 0.05

1 – 200 MW VSC 

converter

1 outage/yr 6 hours 0.000685 1 

1 – 150 kV dc cable 1 outage/100 

mi/40 yr

18 months 0.05 0.0333

1 – 230 kV ac cable 1 outage/100 

mi/40 yr

18 months 0.05 0.0333

1 – set of 

compensating reactors

1 outage/20 yr 2 weeks 0.001923 0.05

Forced Outage Rate q is defined as: (Time on forced outage)

 (Time exposed to forced outage)

A basic application of the binomial probability theorem is undertaken as outlined by 

Billinton8 to evaluate impact of forced outages on energy delivered as well as assess the need 

for spare cables. For the purpose of this evaluation, only Stage 1 development (excluding the 

Stage 2 cable transmission from Maui) is considered. The capacity factors for the 

transmission and the costs of lost energy are the same as applied for the loss evaluation. 

These are 15c

/kwh at a capacity factor of 35%, and 25c/kwh at a capacity factor or 25%. A 

straight line load capacity factor curve is applied.

Other assumptions are:

1. The failure rate for the 3 core AC cable is the same as one HVDC pole cable. This is 

an oversimplified assumption biased in favor of the AC cable. However, there is no 

service record for the 3 core AC cable applied since very few if any are in service at 

230 kV. Failure in a single cable, whether single core coaxial HVDC or 3 core XLPE 

AC cable will be subject to similar failure mechanisms such as defective splicing, 

ground disturbances, anchors or fishing apparatus. Hence the justification for similar 

failure rates for each type of undersea cable.

2. Failures in the DC cables are considered independent events. In otherwords, failure in 

either a pole or metallic return DC cable will not affect the other cable or cables for 

that symmetrical monopole or bipole. However, if one of the DC cables of a 

symmetrical monopole fails, the whole symmetrical monopole is removed from 

service. If one of the DC cables of a bipole with metallic return fails, only one pole is 

removed from service, and operation continues at half power on the other pole. 

The loss of energy delivered (usually designated loss of load expectation or LOLE) for each 

of the preferred options is assembled into Table A-4. This LOLE energy is costed both at 

15c/kwh (35% capacity factor) and at 25c/kwh (25% capacity factor) for a 20 year present 

value accumulation at a discount rate of 5%.

 

8 R. Billinton, Power System Reliability Evaluation, Gordon and Breach, 1970.
- 49 -

Table A-4: Energy lost and its present value cost 

Preferred Option (Stage 1) 1 yr LOLE 

35% CF

MWh

1 yr LOLE 

25% CF

MWh

PV at 

15c/KWh 

$M

PV at 

25c/KWh 

$M

C3-2 400 MW Molokai to 

Koolau - DC 21,702 15,511 40.6 48.3

A3-2 200 MW Molokai to 

Koolau, 200 MW Molokai 

to Iwilei - DC

32,287 23,077 60.4 71.9

A1-2 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Iwilei - DC 

38,962 27,849 72.8 86.8

B3-2 400 MW Molokai to Iwilei 

- DC 24,873 17,778 46.5 55.4

C1-2 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Koolau - DC 

44,182 31,581 82.6 98.4

B1-2 200 MW Molokai to 

Iwilei, 200 MW Lanai to 

Iwilei - DC 

42,483 30,366 79.4 94.6

A1-1 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Iwilei - AC

22,240 15,896 41.6 49.5

Possibility for Spare Cable

The cost of a DC cable for this exercise is estimated at $M2.4/mi and $M3.36/mi for a 3 core 

AC cable. These costs are based on file values for similar undersea cables with the main 

factor being cable weight. Hence the higher cost for the 3 core AC cable compared to the 

lighter solid insulated DC cable. For the 40 mile between Molokai and Koolau, this would be 

$M96 for the DC cable and $M134 for the AC cable. For the most preferred case C3-2 where 

both circuits of Stage 1 are between Molokai and Koolau, the present value cost of 

replacement energy indicated in Table A-4 of $M40.6 to $M48.3 would not justify the cost of 

a spare cable. This same conclusion extends to all preferred options.

A spare cable could be operated in parallel with one of the main cables to reduce losses to 

help justify its cost. The spare DC cable between Molokai and Koolau reduces the variable 

losses for just the cables from 2.5 MW to 1.9 MW. At 25c/kwh, 25% capacity factor and 

present value for 20 years, this saving in losses results in less than $M4 present value saving, 

which does little to justify its need.
- 50 -

Cable Connection Between Lanai and Molokai

The benefit of adding a cable between Lanai and Molokai for the options it could apply was 

investigated and an example is included in option A1-2. A 200 MW symmetrical monopole 

was selected with its individual converters. There is the option of applying a multi-terminal 

HVDC configuration to avoid the capital cost of the independent converters. However, a 

cable or dc side fault might fail the operation of both the Lanai to Oahu and Molokai to Oahi 

cables resulting in a 400 MW loss.

The undersea route selected circumnavigated the west coast of Molokai to avoid the reef. A 

distance of 40 miles was applied justified to avoid breaching the reef. The earlier study9

assumed it was acceptable to cross through the reef but this needs to be justified by 

environmental impact study. The savings in replacement energy to Oahu was not significant 

to warrant the expense. Additional justification will be needed to consider this cable.

Summary 

The present value of capital costs, losses and reliability effects for the selected options with 

revisions are summarized in Table A-5. 

Table A-5: Comparison of Present Value Costs for selected options:

Preferred Option (Stage 1) Present 

Value 

Capital Cost 

$M

PV Losses 

$M

PV 

Reliability 

$M

Total

$M

15c/

kwh 

25c/

kwh 

15c/

kwh 

25c/

kwh 

15c/

kwh 

25c/

kwh 

C3-2 400 MW Molokai to 

Koolau - DC 688 173 268 41 48 902 1004

A3-2 200 MW Molokai to 

Koolau, 200 MW Molokai 

to Iwilei - DC

698 172 267 60 72 930 1037

A1-2 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Iwilei - DC 

711 179 276 73 87 963 1074

B3-2 400 MW Molokai to Iwilei 

- DC 739 176 272 47 55 962 1066

C1-2 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Koolau - DC 

758 185 282 83 98 1026 1138

B1-2 200 MW Molokai to 

Iwilei, 200 MW Lanai to 

Iwilei - DC 

770 187 284 79 95 1036 1149

A1-1 200 MW Molokai to 

Koolau, 200 MW Lanai to 

Iwilei - AC

880 311 492 42 50 1233 1422

 

9 R.W. Beck, “Hawaii Inter-Island Cable Study”, Draft report to the Department of Energy, May 15, 2009
- 51 -

APPENDIX B

Evaluation of SVC Requirement for Inter-Island AC Cable Option

Updated May 2010

Introduction

Concern has been expressed by technical parties that isolation of a wind farm with a long AC 

undersea cable would cause high voltages on the cable and in the wind farm substation, 

requiring fast dynamic VAR support such as an SVC or STATCOM to be installed. The 

requirement for an SVC or STATCOM is justified in this study solely on ensuring the AC 3 

core cables can be energized and operated so that no unacceptable power quality is created in 

the Oahu power system. If an SVC or STATCOM is required in the power system on Oahu 

for system reasons, these have not been considered.

The analysis presented here pertains to Alternative A1-1 (Figure 1). This alternative connects 

up to 600 MW of wind generation to Oahu via AC under-sea cables with both Stage 1 and 

Stage 2 development. The landing sites on the islands are simplifying assumptions for 

comparison purposes and should not be taken as the actual landing sites that will be used as 

several are being considered and evaluated in other study efforts. These over-voltages are 

expected to occur especially following the opening of a breaker at the Oahu “receiving” end 

of the AC cables, effectively isolating the cable and wind farm together from the larger AC 

network. The breaker opening may be spontaneous or following a close-in or remote fault.
- 52 -

Figure 1 Option A1-1: AC Cable Interconnection Alternative. Stage 1 consists of 200 MW, 

230 kV AC 3 core XLPE cable transmission between Molokai and Koolau and also 

between Lanai and Iwilei, each requiring one 3 core cable to be laid. For Stage 2, a 

200 MW, 230 kV AC 3 core cable transmission between Maui and Iwilei is required 

with a reactor station on Lanai. 

Modeling

All modeling and simulation was performed using electromagnetic transient simulator 

PSCAD/EMTDC version 4.210. Both Type 3 (doubly-fed induction generator) and Type 4 

(generator behind a full converter) wind turbine technologies were considered, and the 3-core 

XLPE cable was modeled using the longest expected span, between Oahu and Lanai.

Since the objective of this analysis was to determine voltage conditions at the wind farm after 

the wind farm has been isolated from the network, a simple equivalent model was used to 

represent steady state conditions prior to breaker opening. It was assumed that a worst case 

for overvoltage at the wind turbines would be caused by a high impedance fault followed by a 

breaker opening, or a spontaneous breaker-fail operation.

Cable Representation

The AC cable was modeled using frequency dependent (phase) models in PSCAD/EMTDC, 

providing correct transient response over a wide range of frequencies. The cable model is 

based on the ABB FXBT three-core XLPE cable rated at 733 A and 220/245 kV as shown in 

Figure 2.

 

10 PSCAD/EMTDC is an licensed electromagnetic transients simulator of Manitoba Hydro: 

https://pscad.com/products/pscad/

200 MW

200 MW

Maui

Molokai 

Lanai

200 MW

Iwilei

Koolau

Stage 2 – 230 kV AC 3 Core Cable 

Stage 1- 230 kV AC 3 Core Cable 

Oahu Stage 1 – 230 kV AC 3 Core Cable 

Lanai

Molokai 

Maui
- 53 -

Figure B-2 AC Cable applied for study of 230 kV, 200 MW connection from Lanai to Oahu

The cable as modelled is 100% compensated with shunt reactors to minimize overvoltages 

due to the Ferranti effect, as well as provide smooth voltages upon energization when 

energization is performed using a 2 breaker pre-insertion resistor scheme. The cable studied is 

the 70 mile interconnection between Lanai to Oahu. Since this is the longest section and 

therefore the most challenging to design for, any conclusion on need for an SVC or 

STATCOM will be valid for shorter cables. 

Wind Farm Representation

Both Type 3 (doubly-fed induction generator) and Type 4 (generator behind a full converter) 

turbine types were considered. The size of the wind farm was assumed to be 200 MW, which 

is the largest size expected to be connected radially to the single undersea cable for this 

project. Detailed generic PSCAD models for each type were scaled to 200 MW. Detailed 

models included arresters, protection systems, power electronic interfaces and controls, 

turbine systems, pitch control systems, machine models, and various control modes. 

Overvoltage Control

The issue of concern is shown in Figure B-3. 
- 54 -

Figure B-3 Simplified One-Line Diagram showing radial connection caused by spontaneous breakeropen event

Figure B-4 and Figure B-5 show simulation results for a breaker-fail condition isolating a 200 

MW wind farm with a 70 mile long cable (see Figure 3). For a DFIG turbine (Type 3 - 

Figure 4), upon spontaneous breaker-open operation (occurring at t=5 seconds in simulation 

traces), the voltages at both ends of the cable rise to approximately 1.8 pu before the 

overvoltage protection at the wind farm has time to operate. During this time, surge arresters 

at both ends of the cable and at the 34.5 kV bus absorb energy to prevent the voltage from 

rising further. Approximately 3 cycles after the wind farm substation first detects 

overvoltages, the 230 kV sending end breaker operates. As a redundant protection, a signal is 

also sent via fiber-optic communication from the receiving end breaker to force open the 

sending end 230 kV breaker. Approximately 6 cycles after the wind farm substation first 

detects overvoltages, the 34.5 kV collector feeder breakers and unit protection operates. Full 

converter type turbines (Type 4) experience milder over-voltage conditions during this 

disturbance.

Note that voltages on the AC cable following isolation from the system take a significant 

amount of time to ring down to zero volts, discharging through losses in the cable, shunt 

reactors, and arresters.

138 kV Bus

230 kV Bus

Fibre-optic link

70 mile AC 

under-sea cable

34.5 kV Bus 600 V Bus

200 MW of 

Wind Turbines

Spontaneous 

breaker-open 

operation 

230 kV Bus

Operation due 

to over-voltage 

protection 

Receiving End Sending End 
- 55 -

Figure B-4: Traces showing a POI breaker fail event isolating a radial 70 mile cable with a 200 MW 

wind farm consisting of DFIG (Type 3) turbines.

1.3 pu over-voltage 

initiates trip signal

Breaker opens 

after 3 cycle delay
- 56 -

Figure B-5: Traces showing a POI breaker fail event isolating a radial 70 mile cable with a 200 MW 

wind farm consisting of Full Converter (Type 4) turbines.
- 57 -

Conclusions

The most severe case of AC cable overvoltage occurs when the cable opens first at the 

receiving (Oahu) end. The sending end wind turbine generators at Lanai or Molokai continue 

to pump energy into the cable causing its AC voltage to rise quickly. The overvoltage 

protection on each wind turbine generator (normally set to trip at about 1.2 to 1.25 per unit) 

immediately causes each unit to trip, but because of switching and latency delays, may result 

in the AC overvoltage to continue to rise until restrained by the surge arresters. When a three 

cycle (50 msec) delay is imposed before the actual trip occurs, particularly for the DFIG 

units, the energy absorbed by the surge arresters is well within their capability. This amounts 

to 0.5 kJoule/kV for the 34.5-kV bus arresters and 2.6 kJoule/kV for the 230-kV bus sending 

end and receiving end arresters for the worst case DFIG units. Such arresters are normally 

rated 5 to 13 kJoule/kV. 

As soon as the trip signal is sent by the receiving end (Oahu) protection to trip the receiving 

end 230 kV cable end circuit breaker, that signal is simultaneously sent by fiber to the 

sending end 230-kV cable end circuit breaker for a cross-trip (see Figure 2). The delay in the 

sending end 230-kV cable end breaker opening compared to the receiving end breaker 

opening is just the latency of telecommunication through the fiber to its trip circuit. This may 

be within half a cycle (8.3 msec) instead of the three cycles (50 msec) considered in the above 

analysis. Each wind turbine will also trip on overvoltage as a back-up if the cross-trip from 

Oahu fails.

For the responses observed in this study with worst case results summarized above, it is not 

necessary to have an SVC or STATCOM for dynamic voltage control at the sending end 

system unless required only for the wind turbine generators. The 100% compensation of the 

AC cable means that there is minimum reactive power swing since cable charging is fully 

compensated. It is therefore only the relatively low series impedance of the cable that causes 

reactive power variations with load. With the AC cable energized only from Oahu, the 100% 

compensation also allows for use of pre-insertion resistance using a resistor and two 230-kV 

breakers so that the energization is virtually voltage transient free on the Oahu 230-kV 

busbar. This alleviates the need for an SVC or STATCOM at Oahu. 

There are other issues that appear manageable such as harmonic resonances on the cable. The 

application of an SVC or STATCOM will not solve these issues and so have little impact on 

the recommendation to not require them.
- 58 -

APPENDIX C

Simulation Studies for Inter-Island DC Cable Options

Updated May 2010

Introduction

A detailed simulation model of the Hawaiian Electric Power Company (HECO) electric 

network was developed in three phase representation on PSCAD11. The network of 

generators, transmission lines, transformers and loads was translated directly from the 

PSS/E12 model developed by EPS. The DC cable transmission options outlined in Appendix 

A were added. 

Description of HVDC Cable Models

Each HVDC converter station was modeled as a two level voltage sourced converter (VSC) 

with pulse width modulation switching at 900 Hz. For a 200 MW set of cables, the VSC 

converter at each end was configured as a symmetrical monopole as shown in Figure C-1. 

Two ±150 kV, 667-Amp HVDC cables are provided with each converter.

Figure C-1: PSCAD model of a 2 level symmetrical monopole 200-MW VSC converter

 

11 PSCAD is an licensed electromagnetic transients program from Manitoba Hydro: 

https://pscad.com/products/pscad/: 12 PSS/E is a licensed power system simulation of Siemens PTI.

Rg1

Rg2

Rg3

Rg4

Rg5

Rg6

2

1

2

3

2

5

2

4

2

6

2

2

1000.0 [uF]

0.041 [H]

0.041 [H]

0.041 [H]

1000.0 [uF]

+150 kV

-150 kV
- 59 -

For a 400 MW bipole consisting of two independent two level VSC poles, a bipolar 

configuration was applied as shown in Figure C-2. Here three cables are applied, two at 150 

kV, 1,333 Amps, and the third as a metallic return rated at 50 kV and also 1,333 Amps. 

Figure C-2: PSCAD model of a 400-MW bipolar with 2 level VSC converter poles 

The cables themselves were modeled based on the solid insulation cables of HVDC Light13

 

13 HVDC Light is a registered trademark of ABB.

. 

For the 200-MW symmetrical monopole, each cable with a 667-Amp conductor was 500 mm2

and for the 400-MW bipole of 1,333 Amps, 1,600 mm2. It was assumed each cable was laid 

apart so that there was negligible magnetic coupling between them and to benefit from higher 

rating due to reduced thermal coupling. However, from an environmental aspect, dc magnetic 

field cancellation with the cables laid together may be required, which will necessitate a 

higher rated cable to compensate for the increased thermal coupling. Figure C-3 shows the 

dimensions of the 150-kV HVDC cables modeled, assuming each is buried 1 meter in the 

Rg1

Rg2

Rg3

Rg4

Rg5

Rg6

1

2

3

2

5

2

4

2

6

2

2

2

1000.0 [uF]

0.02 [H]

0.02 [H]

0.02 [H]

Rg1N

Rg2N

Rg3N

Rg4N

Rg5N

Rg6N

1

2

3

2

5

2

4

2

6

2

2

2

1000.0 [uF]

0.02 [H]

0.02 [H]

0.02 [H]

150 kV

-150 kV
- 60 -

seabed. Actual burial depths may be quite different depending on permits, but for studies the 

1 meter is representative and variations to this depth have little impact on the transient 

performance of the cables required for this technical study. 

(a) ±150 kV, 667 A, 500 mm2 cable (b) ±150 kV, 1,333 A, 1,600 mm2 cable 

Figure C-3: HVDC cables modeled as individual co-axial cables 

The bipolar cables are connected with a metallic return conductor that is grounded at one end. 

For the purpose of simulation, the metallic return conductor is the same as the main pole 

conductor cables. This is the traditional way for configuring a metallic return conductor so 

that no dc current ever flows in the sea and seabed. The single ground point at one end of the 

metallic return conductor is necessary to ground the VSC cable system, but it will not be a 

path for return current through the sea and seabed if the bipole is forced to operate as a single 

pole when the other pole is faulted and taken out of operation. The conductor rating of the 

metallic return conductor must be the same as the main pole conductors, but because it is 

grounded at one end, its electrical insulation is less than that of a pole conductor. 

The controls for each pole or symmetrical monopole are separate and independent from any 

other pole or monopole. This is so each pole of 200 MW is the largest outage that a single 

0.01262[m]

Cable # 1

.0255 [m]

.02897 [m]

.0322 [m]

.0372 [m]

.039 [m]

1 [m]

0 [m]

Conductor

Insulator 1

Sheath

Insulator 2

Armour

Insulator 3

0.02257[m]

Cable # 1

.03764 [m]

.0417 [m]

.04548 [m]

.05133 [m]

.0535 [m]

1 [m]

0 [m]

Conductor

Insulator 1

Sheath

Insulator 2

Armour

Insulator 3
- 61 -

component failure can produce and is the maximum outage that is applied in this study. The 

controls for the VSC converters are based on generic strategies. The firing pulses to the 

valves shown in Figures C-1 and C-2 are generated for pulse width modulation at 900 Hz. 

Acceptable power quality is achieved with a supplementary high pass filter tuned at 900 Hz 

as shown in Figure C-4 that is positioned between the VSC converter and the connection 

transformer.

Figure C-4: Supplementary high pass harmonic filter with each VSC converter pole 

There are a number of options for configuring the controls of the VSC converters at the wind 

farm end. What proved to be most effective was to lock the valve firing oscillator to generate 

60-Hz alternating voltage. The ac voltage magnitude generated by the VSC converter at the 

wind farm (sending end) is controlled to provide the wind turbine generators with a stiff 

system to operate into. VSC converters produce the stiff system by creating what is 

designated as “effective short circuit capacity.” It is not the real short circuit capacity that 

synchronous generators or motors provide to the ac system as evident by the significant short 

circuit current they contribute. When a short circuit is applied at or near the terminals of a 

voltage sourced converter, it will either block so that it contributes no fault current 

whatsoever, or its current control limits the short circuit current to be equal or less than the 

rated current of the VSC. Most wind turbine generators on the market today are designed for 

connection to a grid which has adequate short circuit capacity for their operation. The 

strategy of locking the valve firing oscillator to 60 Hz and controlling ac voltage provides the 

necessary short circuit capacity, allowing connection of most types of wind turbine generators 

in the wind farm. 

0.041 [H]

0.041 [H]

0.041 [H]

F = 900.0 [Hz]

F = 900.0 [Hz]

F = 900.0 [Hz]

< To Transformer To VSC Converter >
- 62 -

The independent clock control that locks the 60-HZ frequency at the sending end of the VSC 

cable in effect allows the converter to be like an AC swing generator/motor with infinite 

inertia. It will absorb any power from the wind farms and send it to Oahu or if no wind is 

blowing and the local load on the island needs power, it will generate exactly what the load 

requires, bringing the power from Oahu. It is not unlike having the Oahu terminating AC 

busbar right on the island so that the local load and wind turbines are completely served by 

the Oahu busbar. The disadvantage of this control is that over-current in the VSC converters 

are not so readily controlled.

Any power ramps up or down due to fluctuations in wind will be automatically transmitted to 

Oahu with independent clock control on the VSC converters. This study has not looked at the 

impact of such fluctuations of power on the Oahu electric power system.

The VSC converter connected to the HECO grid controls the dc voltage applied to the DC 

cables. The VSC converter also controls the reactive power it supplies to or takes from the 

AC system. In this way the AC voltage at the 138-kV interconnection busbars are controlled 

by the HECO facilities such as nearby generators and switched capacitor banks. 

Alternatively, AC voltage on the HECO system at the connection busbar can be controlled. 

Wind Turbine Generator Models

Two types of generic but detailed wind turbine generator models are used for the wind farms 

on Molokai and Lanai. One is a doubly fed induction generator (DFIG) that is also known as 

a Class 3 model. GE, Vestas and Mitsubishi make DFIG units available. The other is a full 

converter model (FC) that is also known as a Class 4 model. Siemens and Enercon make FC 

units available. Both classes are used in the cases modeled in the expectation that the wind 

farms may consist of both types from various manufacturers. 

The detail of these Class 3 and 4 wind turbine generators includes the following: 

1. Pitch controller

2. Back to back converters 

3. Vector controls for the back-to-back converters to separate real power and reactive 

power control 
- 63 -

4. Detailed rotating machine models 

5. Protections for overspeed and overvoltage 

Assessment of Performance of DC Cable Transmission

The performance of the options for DC cable transmission is measured by evaluating their 

responses of various disturbances and faults. The HECO grid must survive in terms of 

maintaining acceptable AC voltage and frequency, and maintain angle stability between the 

generators. The DC voltage and current in the VSC converters and undersea cables must 

remain within ratings, and the connection provided for the wind farms on Molokai and Lanai 

must also maintain acceptable levels of AC voltage and frequency. 

Most Severe Single Contingency Disturbance

The most severe single contingency disturbance is an AC bus fault at the terminating 

interconnection busbar of the DC cable transmission, with delayed clearing which results in a 

200-MW pole or monopole being disconnected as shown in Figure C-5. 

Figure C-5: Opening the DC cable at the point of interconnection to the AC grid 

This fault being a bus fault at Iwilei or Koolau has a severe impact on the HECO grid. (The 

landing sites on the islands are simplifying assumptions for comparison purposes and should 

not be taken as the actual landing sites that will be used as several are being considered and 

evaluated in other study efforts). The power from the wind turbine will continue flowing into 

the cable through the converter at the sending (wind farm) end, causing the voltage on the DC 

cable to rise. Ideally the sending end circuit breaker could be transfer tripped by the same 

protection signal that was sent to the receiving end circuit breaker through a high speed fiber 

optic communication circuit. Since signal delays or failures need to be designed for, 

protection against overvoltage on the DC cable is achieved by a supplementary DC chopper 

Circuit breaker opens 

to clear fault

Sending End DC Chopper

Fault

Receiving End

Circuit breaker opens on 

transfer trip from 

receiving end breaker
- 64 -

circuit as shown in Figure C-6. The DC chopper is a resistor that is switched in and out across 

the receiving end of the cable with a solid state switch. It can switch very quickly on 

detection of overvoltage building up on the DC cable. However, the DC chopper cannot 

operate indefinitely, and so the wind turbine generators will have to be disconnected from 

feeding into the DC cable by a secondary protection circuit if the primary transfer trip is 

delayed or fails.

This fault is represented in simulation with DC Option B1-2 which has a 200-MW monopole 

from Molokai and a 200-MW monopole from Lanai with both terminating at Iwilei. The wind 

farms on each island are operating at their full 200 MW rating. Figure C-6 shows the 

simulated results with the key to these specific time based plots and others as follows:

AC Volts on Oahu

VIwilei: 138 kV AC rms volts in per unit (pu) at Iwilei bus 130 

 VKoolau: 138 kV AC rms volts in per unit (pu) at Koolau bus 150 

Generator rotor angles

Ang-AES: AES-1 unit at bus 1331 

Ang-Wai: WAI-5 unit at bus 1205 

Ang-Kahe6: KAHE-6 unit at bus 1146 

AC Volts at Wind Farms on Molokai and Lanai 

 VMolokai: 33 kV AC rms bus volts in per unit (pu) at the Molokai wind farm 

VLanai: 33 kV AC rms bus volts in per unit (pu) at the Lanai wind farm 

Frequency on Oahu and at the Wind Farms on Molokai and Lanai 

FIwilei: Frequency of HECO’s system measured at Iwilei in Hz

FMolokai: Frequency of the Molokai wind farm in Hz 

FLanai: Frequency of the Lanai wind farm in Hz 

Power in DC poles 

 Power Pole 1: DC Power in one pole in MW 

 Power Pole 2: DC Power in the other pole in MW 

Voltage on DC cables when one 400 MW bipole 

VcableP: DC volts on positive pole cable in kV 

VcableN: DC volts on negative pole cable in kV 

Voltage on DC cables when two 200 MW symmetrical monopoles 
- 65 -

 VpMolokai: DC volts on positive polarity cable of monopole from Molokai in kV 

 VnMolokai: DC volts on negative polarity cable of monopole from Molokai in kV 

 VpLanai: DC volts on positive polarity cable of monopole from Lanai in kV 

 VnLanai: DC volts on negative polarity cable of monopole from Lanai 

Figure C-6: DC Cable Option B1-2, a 200-MW monopole from Molokai and also from Lanai 

both terminating at Iwilei. 12 cycle, 3-phase bus fault at Iwilei causes monopole 

from Lanai to trip out of service. DC chopper not in service 

Option B1-2: 3Phase Fault at Iwilei, Monopole to Lanai Tripped

Secs 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

350 

400 

450 

500 

550 

600 

650 

700 

750 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VMolokai VLanai

58.00 

58.50 

59.00 

59.50 

60.00 

60.50 

61.00 

61.50 

62.00 

Frequency (Hz)

FIwilei FMolokai FLanai

0 

50 

100 

150 

200 

250 

Power (MW)

Power Molokai Power Lanai

-300 

-200 

-100 

0 

100 

200 

300 

Cable Volts (kV)

VpMolokai VnMolokai VpLanai VnLanai
- 66 -

There are several significant results that are shown here in Figure C-6, which highlight the 

seriousness of this severe receiving end fault:

1. While the fault is on and waiting to be cleared, the power generated at the two wind 

farms on Molokai and Lanai still feed power into the cables. In this case there is no 

indication at the wind farms at the sending end of the DC cables that there is a fault. 

The DC voltages on the cables commence to increase during the course of the fault. 

The DC chopper is not in service so the overvoltage on the DC cables can be 

observed. The DC voltage approached 1.5 per unit. The DC cable and converters 

should be capable of withstanding this level of overvoltage. Both the DC cable and 

converters will be designed to withstand a 2.0 per unit temporary overvoltage that will 

result from a DC cable fault. However, if this fault takes longer to clear, then there is a 

possibility that the DC overvoltage would be greater than 2.0 per unit without the DC 

chopper. 

2. The fault is cleared after 12 cycles (0.2 seconds) which in this case causes the 

monopole from Lanai to trip out of service. The circuit breaker to the converter on 

Lanai is transfer tripped from Lanai with the protection signal that trips the receiving 

end circuit breaker being transmitted to Lanai through a fiber channel. The firing 

pulses to the converters at each end of the tripped monopole to Lanai are also blocked 

so that the DC cable and converters are taken from service. However, the DC cable 

and converters remain charged in excess of rated ±150 kV. 

3. When the monopole to Lanai is tripped and blocked, AC frequency control at Lanai is 

lost, and the wind turbine generators will require their protections to operate and take 

the wind farm off-line.

4. After the three-phase fault is cleared at Iwilei, the DC monopole to Molokai remains 

in service and recovers to its pre-disturbance power level. The HECO grid has cleared 

a severe AC fault at Iwilei, its generators remain synchronized but swinging, and has 

lost the 200-MW infeed from Lanai. This simulation shows the transient post 

disturbance AC voltage that occurs which suffers a transient dip down to about 0.92 

per unit. The post disturbance grid frequency on the HECO system reaches 61 Hz 

based on this model. 
- 67 -

Impact of the DC Chopper

The same disturbance of a 12 cycle three phase fault at Iwilei with 200-MW DC monopoles 

from Molokai and Lanai but with the DC chopper active is shown in Figure C-7 just for the 

DC cable voltages. Note that the DC chopper switches on the DC monopoles at 

approximately 0.24 and 0.31 seconds. When it switches off after the fault has cleared, there is 

some residual voltage ringing on the cable due to oscillations defined by the cable impedance, 

the DC side surge (smoothing) inductor and the VSC converter capacitance. The DC 

temporary overvoltage is limited to less than 1.5 pu compared with the nearly 2.0 pu with no 

DC chopper. 

Figure C-7: DC Cable Option B1-2, 12 cycle, 3 phase bus fault at Iwilei causes monopole 

from Lanai to trip out of service, DC chopper operating limiting DC overvoltage 

to 1.47 pu 

If the DC Cable transmission of 200-MW symmetrical monopoles each from Molokai and 

Lanai both terminate into Koolau as in Case C1-2, and the three phase, 12 cycle AC fault is 

applied to the 138-kV terminating AC busbar at Koolau, then the system performance is 

shown in Figure C-8. Similarly to the case shown in Figures C-6 and C-7, the AC bus fault 

causes the symmetrical monopole from Lanai to be disconnected at the receiving end leaving 

only the DC Cable from Molokai in service. The DC chopper is in-service and functioning for 

the simulation shown in Figure C-8. The same key to understanding the graphs applies. 
- 68 -

Figure C-8: DC Cable Option C1-2, 12-cycle, 3-phase bus fault at Iwilei causes monopole 

from Lanai to trip out of service. Monopole from Molokai remains operational. 

DC chopper in service 

Option C1-2: 3 Phase Fault at Koolau, Monopole to Lanai Tripped

0.00 0.50 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

350 

400 

450 

500 

550 

600 

650 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VMolokai VLanai

58.00 

58.50 

59.00 

59.50 

60.00 

60.50 

61.00 

61.50 

62.00 

Frequency (Hz)

FIwilei FMolokai FLanai

0 

50 

100 

150 

200 

250 

Power (MW)

Power Molokai Power Lanai

-200 

-100 

0 

100 

200 

300 

400 

Cable Volts (kV)

VpMolokai VnMolokai VpLanai VnLanai
- 69 -

Severe Disturbance with a Bipolar DC Cable

A similar problem results when the DC cable transmission to the HECO grid system is 

through a 400-MW bipole. The power through the remaining pole may recover to twice its 

rating as shown in Figure C-9. 

Figure C-9: DC Cable Option C3-2: With a 400-MW bipole from Molokai to Koolau, and a 

three phase fault at Koolau tripping one pole from service. Power order reduction 

applied to the wind farm to bring total wind farm generated power to within the 

rating of the pole remaining in service. 

The sending end wind farm could be either on Molokai or Lanai and would be rated for 400 

MW. It is necessary that each pole to be located on the AC terminating busbar so that no one 

busbar fault could remove both poles permanently from service. Therefore a busbar fault at 

Option C3.2: 3 Phase Fault at Koolau, 1 DC Pole tripped

 Secs 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

350 

375 

400 

425 

450 

475 

500 

525 

550 

575 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VMolokai

59.00 

59.50 

60.00 

60.50 

61.00 

Frequency (Hz)

FIwilei FMolokai

0 

50 

100 

150 

200 

250 

300 

350 

400 

Power (MW)

Power Pole1 Power Pole2

-1.50 

-1.00 

-0.50 

0.00 

0.50 

1.00 

1.50 

Cable Volts (pu)

VcableP VcableN
- 70 -

the terminating busbar would only remove one pole from continued operation. The very short 

thermal inertia of the valves in a VSC converter would normally not accommodate such an 

overload to the remaining pole in service as shown in Figure C-9. The options to deal with 

this are:

1. Purchase the VSC converters with enough rating to accommodate the overload. 

2. Require that the wind turbine generators that connect to the sending end of the bipole 

have a power order controller. When the wind farm receives a signal that one pole is 

removed from service for one reason or another, the power order controller would 

reduce the total power from the wind turbine generators to a level that could be 

accommodated by the remaining pole of the DC Cable transmission. Such a function 

has been provided in the Horns Rev wind farm in the North Sea off the coast of 

Denmark where the wind turbine generators are DFIG units. The speed of the power 

down would have to be specified to occur within the rating capabilities of the pole left 

in service. The plot of Figure C-9 shows how such a power down might apply. 

However there is still a power overshoot for the operating pole for which it would 

need to be rated for. 

3. Apply a transfer trip of wind turbine generator units at the wind farm. When the 

protection system for the DC Cable transmission detects that a pole is to be tripped 

from operation, wind turbine generators are immediately transfer tripped so that no 

overload occurs on the remaining pole after it recovers from the initiating fault. This 

is shown in Figure C-10 where the 400-MW bipole is based on Option B3-2 which 

terminates at Iwilei for a 400-MW radial transmission from Molokai. 
- 71 -

Figure C-10: DC Cable Option B3-2: With a 400-MW bipole from Molokai to Iwilei, and a 

three-phase fault at Iwilei tripping one pole from service. Transfer tripping of 

selected wind turbine generator units to bring total wind farm generated power to 

within the rating of the pole remaining in service.

Option B3-2: 3 Phase Fault at Iwilei, 1 DC Pole tripped

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

360 

560 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VLanai

59.00 

59.50 

60.00 

60.50 

61.00 

Frequency (Hz)

FIwilei FMolokai

0 

50 

100 

150 

200 

250 

Power (MW)

Power Pole1 Power Pole2

-1.50 

-1.00 

-0.50 

0.00 

0.50 

1.00 

1.50 

Cable Volts (pu)

VcableP VcableN
- 72 -

Impact of Faults on Oahu on Wind Turbine Generators on Molokai and Lanai

If the DC Cable feeders to Oahu from Molokai and or Lanai remain in service through a 

system fault or disturbance on the HECO grid, then they have the ability to provide 

significant buffering to the wind turbine generators. This is because the voltage sourced 

converters are relatively impervious to AC side faults and disturbances. The DC cable voltage 

may increase during the fault or disturbance, but this is managed by the DC chopper as shown 

in Figures C-7 to C-10. 

By way of example, the three-phase, 12-cycle fault is applied to the Koolau 138-kV AC bus 

for the configuration of Option A1-2. This case has a radial 200 MW symmetrical monopole 

from Iwilei to Lanai and a radial 200-MW symmetrical monopole from Koolau to Molokai. 

In addition, there is a 200-MW VSC transmission interconnection between Molokai and 

Lanai operating initially with a 20-MW power schedule from Molokai to Lanai. The response 

of the AC and DC system including the wind farms on Molokai and Lanai to this severe 

disturbance on Oahu is shown in Figure C-11. The following observations can be made: 

1. The AC voltages on Molokai (VMolokai) and on Lanai (VLanai) are minimally 

impacted rising temporarily from near 1.0 pu to 1.06 pu during the fault and 

immediately after it is cleared. Then falling temporarily to 0.91 pu before recovering 

to 1.0 pu. 

2. The frequencies on Molokai and Lanai during and after the fault at Koolau remain 

close to 60 Hz, whereas the frequency on Oahu increases to 60.8 Hz. 

3. The power into the DC Cable transmission from the wind farms remains fairly 

constant through and after the fault at Koolau. 

Consequently because the AC voltage and frequency that the wind farms on Molokai and 

Lanai are connected to stay relatively steady, the impact to the wind turbine generators on 

both islands is minimal for this severe AC fault at Koolau. 
- 73 -

Figure C-11: DC Cable Option A1-2: With a 200-MW monopole from Molokai to Koolau, a 

200 MW monopole from Lanai to Iwilei and a 200-MW monopole from 

Molokai to Lanai. A three phase fault for 12 cycles (0.2 seconds) is applied at 

Koolau with all DC Cable transmissions remaining operational.

Option A1-2: 3 Phase fault at Koolau 138 kV bus, DC Cable Transmission Remain in Service

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

350 

400 

450 

500 

550 

600 

650 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VMolokai Lanai

58.00 

58.50 

59.00 

59.50 

60.00 

60.50 

61.00 

61.50 

62.00 

Frequency (Hz)

FIwilei FMolokai FLanai

0.0

225 

Power (MW) (MW)

Power Molokai-Koolau Power Lanaii-Iwilei Power Molokai-Lanaii

-300 

-200 

-100 

0 

100 

200 

300 

Cable Volts (kV)

VpMolokai VnMolokai VpLanai VnLanai
- 74 -

Impact of Faults on Molokai or Lanai on the HECO Grid on Oahu

The consequence of severe AC system faults at Molokai or Lanai on the HECO grid on Oahu 

is also minimal due to the buffering properties of the VSC cable transmission. If the fault at a 

wind farm clears without significant loss of wind turbine generators, the impact at the 

receiving end will not be significant. If a large number of wind turbines trip because of the 

disturbance, then the loss of generation will reflect through to the HECO grid system which 

will have to adjust accordingly. 

An interesting case for this disturbance is with DC Option A3-2 as shown in Figure C-12. 400 

MW of wind turbine generation is located on the one island, which in this instance is 

Molokai. A 200-MW symmetrical monopole DC Cable feeds to Koolau from Molokai and 

another feeds to Iwilei from Molokai. A severe three phase AC fault is applied on a 33-kV 

wind farm collector circuit on Molokai that clears in 12 cycles (0.2 seconds) without loss of 

wind turbines. 

The impact on the HECO grid is the AC voltage at both Koolau and Iwilei dips to 0.83 pu for 

the duration of the fault. DC cable voltage starts to fall and giving up power that feeds into 

the HECO grid system helping maintain its frequency. However after the fault is cleared and 

the Molokai AC voltage recovers, power is pumped into recovering the DC voltage to charge 

the cable and VSC capacitors at the expense of power being delivered into the HECO grid. At 

this point the frequency of the HECO grid commences to fall as a result of the temporary loss 

of delivered power as a consequence of the fault. 

A control interaction of about 60 Hz occurs between the two VSC Cable transmission 

systems at Molokai. This is a control instability that slowly damps out. Closer inspection 

indicates that the DFIG wind turbine generators are included in the interaction but the FC 

units appear unaffected. The interaction has no significant impact on the delivery of power to 

the HECO grid system, but it has implications in coordinating the controls of the VSC Cable 

transmission lines and wind turbine generators. The contracts involving the connection of the 

VSC Cable transmission lines to the HECO grid and the interconnection agreements for 

connecting wind turbine generators to their sending end converters will require procedures 

and mechanisms in place to investigate and remedy such interactions if they are found to 

show up during design or operation. 
- 75 -

Figure C-12: DC Cable Option A3-2: With a 200-MW monopole from Molokai to Koolau 

and a 200-MW monopole from Molokai to Iwilei. A three-phase fault for 12 

cycles (0.2 seconds) is applied at Molokai with all DC Cable transmissions 

remaining operational. 

Option A3-2: 3 Phase Fault at Molokai, DC Cable Transmission Remain in Service

Secs 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

AC Volts (pu)

VIwilei VKoolau

300 

400 

Angle (Deg)

Ang-AES Ang-Wai Ang-Kahe6

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

V at Molokai (pu)

VMolokai VMolokai2

58.00 

58.50 

59.00 

59.50 

60.00 

60.50 

61.00 

61.50 

62.00 

Frequency (Hz)

FIwilei FMolokai FMolokai2

0 

50 

100 

150 

200 

250 

Power (MW)

Power Molokai-Koolau Power Molokai-Iwilei

-200 

-150 

-100 

-50 

0 

50 

100 

150 

200 

Cable Volts (kV)

VpMolokai VnMolokai VpMolokai2 VnMolokai2
- 76 -

Coordinating Design between the VSC Transmission and the Wind Turbine Generators

Further to the control interaction observed in the study case of Figure C-12, there may not be 

much possibility for coordinated design of controls and protections between the wind turbine 

generators, the VSC transmission and the HECO grid. The proprietary nature of the controls 

of wind turbine generators and VSC transmission systems provides little opportunity for 

sharing of key designs between the various suppliers, particularly if they are competitors. The 

design of the VSC transmission controls and protections is the most important and this must 

be reflected in the technical specification required to establish a satisfactory contract with the 

DC equipment supplier. The technical specification must contain an acceptable performance 

requirement that the contracted DC equipment supplier must meet.

The performance standard for the controls, protection and rating design of the VSC 

transmission from the wind farms on the islands of Molokai and Lanai to Oahu must be 

robust and broadband enough to accommodate any type of modern wind turbine generator. A 

solid 60 Hz frequency and AC voltage must be provided for the wind turbine generators by 

the VSC transmission. The performance standard must ensure that the HECO grid is 

minimally impacted at the delivery points of the VSC transmission. 

If done well, the VSC transmission will also act as a buffer from AC faults on Molokai and 

Lanai so the HECO grid system is minimally impacted.
- 77 -

APPENDIX D

Request for Information from DC Converter and Cable Manufacturers

October 9, 2009, Updated November, 2009. 

 

To: 

DC Converter Station Suppliers (ABB, Areva and Siemens)

OAHU WIND INTEGRATION AND TRANSMISSION STUDY (OWITS)

BUDGET PRICING OF INTER-ISLAND CABLE OPTIONS

The US Department of Energy through the National Renewable Energy Laboratory (NREL) 

invites you to respond to this request for budget pricing information on various options for 

HVDC converter and AC substations terminating undersea electric power cable transmission 

from the Hawaiian Islands of Molokai, Lanai and Maui to Oahu. 

Return Information

Please return the completed budget pricing form (pages 7 to 17 below) to:

National Renewable Energy Laboratory

Attn: David Corbus, 

1617 Cole Boulevard

Golden, CO 80401-3393

USA

Email: David.Corbus@nrel.gov 

By November 20, 2009.

Confidentiality

The information received from NREL through this request is confidential and must be 

treated as such. Likewise, the recipient of this request will not have their name or 
- 78 -

association with the information submitted to NREL on the budget pricing form disclosed to 

anyone other than the team specifically assigned to evaluate this project.

Background to the Project

The Hawaii Clean Energy Initiative (HCEI) is a multiyear initiative with the State of Hawaii 

with an objective to provide technical support to the State to meet a self-imposed goal of 

70% clean energy use through renewables and efficiency in the electricity and 

transportation sector by the year 2030 (40% by renewables).

One of the driving forces for FY09/10 work is the signed agreement between the State and 

Hawaiian Electric Company (HECO), Inc. that includes a combined commitment of up to 100 

MW of on-island wind resources and up to 400 MW of wind on the Islands of Lanai and 

Molokai via an inter-island cable that would bring that wind energy to Oahu.

 

To support the HCEI and HECO efforts, the Oahu Wind Integration and Transmission Study 

(OWITS) study has been initiated. The goal of OWITS is to help stakeholders, with special 

emphasis on the utility and the state, to understand the costs and operating impacts of 

significant amounts of wind power on their island grids and to help them identify the 

technical requirements of and configuration for an undersea inter-island cable to transmit 

electricity from large wind and or solar systems from one island to another island.

The HECO system on Oahu is today an island system without inter-ties to neighboring 

islands. With potential for at least 100 MW of on-island wind generation, the impacts of 

additional wind variability and transient impacts on grid reliability due to connecting 

neighbor island wind all need to be carefully considered. 

HECO currently runs with a spinning reserve sufficient to cover the loss of the largest single 

generator connected to the system. The largest single generator currently on the HECO 

system is AES at 180 MW. As such, when AES is online the system is operated with a 

spinning reserve of approximately 180 MW. Given this spinning reserve requirement and 

the dynamic impact to the system, it can be assumed that the HECO system will not be able 

to withstand the instantaneous loss of all 400MW from the Lanai and Molokai wind plants 

and the cable system will need to be designed such that only 200 MW can be disconnected 

due to any single point of failure.

The HECO system has a limited ability to withstand the switching transients associated with 

the loss of any single compensation system. As such, the voltage transients associated with 

the switching or failure of reactive compensation for the AC system need to be evaluated 

and acceptable limit levels considered. In addition, a reactive power system to address any 

voltage support and control requirements on the submarine cables (i.e. minimum power 

flow of 0 MW to the total maximum power flow of 200 MW per circuit) will need to be 

addressed as part of a design conceptualization and configuration trade-off effort.
- 79 -

There is a number of cable routing possibilities from the islands of Molokai, Lanai and Maui 

to Oahu. One such possibility is shown in Figure 1. With up-to-date cable and termination 

pricing, it will be possible to select a preferred configuration for the interconnections. Both 

AC and HVDC options are under consideration. The HVDC options will be with Voltage 

Sourced Converters (VSC).

The connections from Molokai and Lanai to Oahu can be considered as a first stage 

development and can be scheduled to be place in service in a practical sequence. The 

interconnection from Maui to Oahu is a second stage development and can be considered to 

be in service 5 years after stage 1 is fully operational. 

Figure 1: Possible cable interconnections between the Hawaiian Islands.

Budget Pricing Requirements

Budget pricing is required for engineering, procurement and construction (EPC) of AC and 

HVDC stations. Spare transformers and AC shunt reactors are to be included in the terminal 

station prices along with inclusion of normally supplied spares for other equipment. 

The budget prices are to be submitted as if they were being quoted for immediate 

installation of all stages, and are to be submitted in current US dollars.

Site licensing and preparation for terminal stations are not to be included in the budget 

prices submitted. 

For the purpose of pricing, the AC systems on Molokai, Lanai and Maui will be wind farms 

consisting of various types of wind turbine generators consisting mainly of doubly fed 

induction generators (DFIG) and full converter (FC) units. The terminal stations must be able 

to support these generators with adequate AC voltage and frequency control. 

The load on the receiving end of the interconnections on Oahu will be the HECO system.
- 80 -

HVDC Converter Stations

Two VSC converter station options will be priced. These are:

DC-1: 200-MW symmetrical monopole.

DC-2: 400-MW bipole, so that each pole operates independent of the other pole, with both 

poles constructed at the same time.

DC-3: 400-MW bipole, so that each pole operates independent of the other pole, but with 

each pole constructed at different times. In other words, the pricing of a 200-MW pole will 

be separately provided with the consideration that they will be constructed separately.

Nominal DC voltage: ±150 kV

General Data for the AC systems

Table 1 Sending end systems at Molokai, Lanai and Maui

Nominal AC Voltage 138 kV AC voltage to be controlled by VSC 

converter Maximum continuous voltage 145 kV

Minimum continuous voltage 131 kV 

Nominal frequency 60 Hz AC frequency to be controlled by 

VSC converter

Short circuit capacity ? As provided by wind turbine 

generators and VSC converter

Environmental conditions Tropical

Altitude Near sea level

Table 2: Receiving end HECO’s system at Oahu

 

Nominal AC Voltage 138 kV AC voltage control with droop 

characteristic or constant reactive 

power option

Maximum continuous voltage 145 kV 

Minimum continuous voltage 131 kV 

Nominal frequency 60±0.5 Hz Frequency controlled by HECO

Maximum short circuit capacity 5,000 MVA

Minimum short circuit capacity 1,590 MVA

Environmental conditions Tropical

Altitude Near sea level
- 81 -

AC Terminal Stations

Budget pricing is required for the AC terminal stations based on an AC cable voltage of 230 

kV. The components for a terminal substation are shown in the single line diagram of Figure 

2. The cables are assumed to be shunt compensated at near 100%. The cable will be 

energized by a two breaker pre-insertion resistor scheme as shown in Figure 2.

 

Figure 2: Single line diagram of an AC terminal substation at both sending and receiving ends 

of the AC Cable

Further study will be undertaken to finalize the configuration of the AC substations, which 

may impact sizing of the shunt reactors and SVC, as well as the winding configuration of the 

230/138-kV transformer. However, for this budget pricing exercise, the layout in Figure 2 

will be applied. The options for pricing the substations terminating the AC cable will vary 

according to the ratings of the shunt reactor and SVC. The options for pricing are presented 

in Table 3. Each reactor bank shall include a spare phase for rapid (within 2 days) insertion 

time.

Table 3: AC terminal substation pricing options

Substation Component AC-1 AC-2 AC-3 

230 kV Shunt Reactors 1-96 MVAR 1-120 MVAR 1-170 MVAR

SVC ±30 MVAR ±40 MVAR ±50 MVAR

The remaining components in the AC substation will remain the same for all three options 

and will include:

• 240 MVA autotransformer and spare phase/transformer 

• 2 – 230 kV circuit breakers and disconnect switches 

• 5 Mjoule, 230-kV pre-insertion resistor

• 3 – 138 kV-circuit breakers and disconnect switches

• 230-kV and 138-kV surge arresters

SVC

230 kV AC Cable Entry

Shunt Reactor

240 MVA 

Autotransformer 

230/138 kV 

138 kV busbar

Two breaker preinsertion resistor 

scheme 
- 82 -

• Reactor switch

• 230-kV and 138-kV buswork

• Instrument transformers

• Protection systems

The pricing for the transformers, shunt reactors, pre-insertion resistor and SVCs to be 

separately identified for each AC option.

There is expected to be a space requirement for some substation locations under 

consideration and budget prices are requested for each of the three options both with air 

insulated substation (AIS) and gas insulated substation (GIS).

Cable Options 

The HVDC cables will be for operation with voltage sourced converters at ±150 kV. AC cable 

options are being considered for 230 kV. Budget prices for the cable options are being 

requested separately.
- 83 -

EQUIPMENT SUPPLIER'S NAME 

 

Project: Oahu Wind Integration and Transmission Study (OWITS)

HVDC Converter and AC Substations

BUDGET PRICING FORM

PRICING 

Firm lump sum prices are to be provided for to all labor, materials, equipment, required 

spares, labor supervision, construction tools and equipment, construction services and utilities 

to design, furnish, erect and commission the HVDC converter station and AC substation 

options. 

For the purpose of proposal evaluation the Equipment Supplier shall break down the 

estimated lump sum price for the three HVDC Voltage Sourced Converter Station options 

(considering one end only) as follows:

HVDC Converter Station Option DC-1: 200-MW symmetrical monopole.

 1. Basic Converter Station $___________________ 

 2. Recommended Spares Cost $___________________ 

 3. Duty, based on a _____% rate $___________________ 

 4. Insurance $___________________ 

5. Transportation $___________________ 

 6. Total $___________________

Operating Data for Option DC-1 

 7. Largest single contingency loss (MW) ______________ 

 8. Inductive reactive power capability at full load (MVAR) ______________ 

 9. Capacitive reactive power capability at full load (MVAR) ______________ 

 10. 45 minute overload rating of converter (MW) ______________ 

 11. Estimated converter station size (feet2

) ______________ 
- 84 -

HVDC Converter Station Option DC-2: 400-MW bipole, so that each pole operates 

independent of the other pole, with both poles constructed at the same time. 

 1. Basic Converter Station $___________________ 

 2. Recommended Spares Cost $___________________ 

 3. Duty, based on a _____% rate $___________________ 

 4. Insurance $___________________ 

 5. Transportation $___________________ 

 6. Total $___________________

Operating Data for Option DC-1 

 7. Largest single contingency loss (MW) ______________ 

 8. Inductive reactive power capability at full load (MVAR) ______________ 

 9. Capacitive reactive power capability at full load (MVAR) ______________ 

 10. 45 minute overload rating of converter (MW) ______________ 

 11. Estimated converter station size (feet2) ______________ 

HVDC Converter Station Option DC-3: 400-MW bipole, so that each pole operates 

independent of the other pole, but with each pole constructed at different times. In other 

words, the pricing of a 200-MW pole will be separately provided with the consideration that 

they will be constructed separately.

 1. Basic Converter Station with pole 1 constructed $___________________ 

 2. Recommended Spares Cost $___________________ 

 3. Duty, based on a _____% rate $___________________ 

 4. Insurance $___________________ 

 5. Transportation $___________________ 

 6. Total Pole 1 $___________________ 

 7. Pole 2 as if separately and independently built $___________________ 

 8. Recommended Spares Cost $___________________ 

 9. Duty, based on a ______% rate $___________________ 

 10. Insurance $___________________ 

 11. Transportation $___________________ 

 12. Total Pole 2 $___________________

Operating Data for Option DC-3 
- 85 -

 13. Largest single contingency loss (MW) ______________ 

 14. Inductive reactive power capability at full load (MVAR) ______________ 

 15. Capacitive reactive power capability at full load (MVAR) ______________ 

 16. 45 minute overload rating of converter (MW) ______________ 

 11. Estimated converter station size (feet2) ______________ 

AC AIS Substation Option AC-1a with 240-MVA, 230/138-kV transformer and spare 

1 – 96 MVAR, 230-kV shunt reactor and spare, 1 - ±30 MVAR, 138-kV SVC 

and 1-5MJ, 230-kV resistor with by-pass circuit breaker 

 1. 1 – 240-MVA, 230/138-kV transformer $___________________ 

 2. 1 – 96 -VAR, 230-kV shunt reactor $___________________ 

 3. 1 - ±30-MVAR, 138-kV SVC $___________________ 

 4. 230-kV, 5-MJ resistor and by-pass circuit breaker $___________________ 

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-1a 

 11. Estimated substation size (feet2

) ____________________ 

AC AIS Substation Option AC-2a with 240-VA, 230/138-kV transformer and spare, 1 

– 120 MVAR, 230-kV shunt reactor and spare, 1 - ±40 MVAR, 138-kV SVC and 1-

5-MJ, 230-kV resistor with by-pass circuit breaker 

 1. 1 – 240-MVA, 230/138-kV transformer $___________________ 

 2. 1 – 120-MVAR, 230-kV shunt reactor $___________________ 

 3. 1 - ±40-MVAR, 138-kV SVC $___________________ 

 4. 230-kV, 5-MJ resistor and by-pass circuit breaker $___________________ 

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 
- 86 -

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-2a 

 11. Estimated substation size (feet2) ____________________ 

AC AIS Substation Option AC-3a with 240-MVA, 230/138-kV transformer and spare, 

1 – 170 MVAR, 230-kV shunt reactor and spare, 1 - ±50 MVAR, 138 kV 

SVC and 1-5MJ, 230-kV resistor with by-pass circuit breaker. 

 1. 1 - 240 MVA, 230/138-kV transformer $___________________ 

 2. 1 – 96 MVAR, 230-kV shunt reactor $___________________ 

 3. 1 - ±50 MVAR, 138 kV SVC $___________________ 

 4. 230-kV, 5-MJ resistor and by-pass circuit breaker $___________________ 

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-3a 

 11. Estimated substation size (feet

2

) ____________________ 

The estimated lump sum price for three GIS HVAC Substation 

options (considering one end only) as follows:

AC GIS Substation Option AC-1b with 240 MVA, 230/138-kV transformer and spare 

1 – 96 MVAR, 230-kV shunt reactor and spare, 1 - ±30 MVAR, 138-kV SVC 

and 1-5MJ, 230-kV resistor with by-pass circuit breaker 

 1. 1 - 240 MVA, 230/138-kV transformer $___________________ 

 2. 1 – 96 MVAR, 230-kV shunt reactor $___________________ 

 3. 1 - ±30 MVAR, 138-kV SVC $___________________ 

 4. 230-kV, 5-MJ resistor and by-pass circuit breaker $___________________ 
- 87 -

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-1b 

 11. Estimated substation size (feet2) ____________________ 

AC GIS Substation Option AC-2b with 240-MVA, 230/138-kV transformer and 

spare, 1 – 120 MVAR, 230-kV shunt reactor and spare, 1 - ±40 MVAR, 138-kV SVC 

and 1-5MJ, 230-kV resistor with by-pass circuit breaker 

 1. 1 - 240 MVA, 230/138-kV transformer $___________________ 

 2. 1 – 120 MVAR, 230 kV-shunt reactor $___________________ 

 3. 1 - ±40 MVAR, 138-kV SVC $___________________ 

 4. 230-kV, 5-MJ resistor and by-pass circuit breaker $___________________ 

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-2b 

 11. Estimated substation size (feet2

) ____________________ 

AC GIS Substation Option AC-3c with 240-MVA, 230/138-kV transformer and spare, 

1 – 170 MVAR, 230-kV shunt reactor and spare, 1 - ±50 MVAR, 13- kV SVC and 1-

5MJ, 230-kV resistor with by-pass circuit breaker. 

 1. 1 - 240 MVA, 230/138-kV transformer $___________________ 

 2. 1 – 96 MVAR, 230-kV shunt reactor $___________________ 

 3. 1 - ±50 MVAR, 138-kV SVC $___________________ 
- 88 -

 4. 230-kV, 5 MJ resistor and by-pass circuit breaker $___________________ 

 5. Remainder of Substation $___________________ 

 6. Recommended Spares Cost $___________________ 

 7. Duty, based on a _____% rate $___________________ 

 8. Insurance $___________________ 

 9. Transportation $___________________ 

 10. Total $___________________ 

Operating Data for Option Ac-3c 

 11. Estimated substation size (feet2) ____________________ 

OFFER OF ALTERNATIVES

The Equipment Supplier shall provide budget prices on the 

work exactly as requested. However, the Equipment Supplier is 

invited to offer alternatives. If an alternative is offered, the 

Equipment Supplier shall state clearly in what way the work 

differs from what has been requested, why such alternative 

work is offered and how, in the Equipment Supplier’s opinion, 

the alternative configuration and product features would better 

suit the operational environment of an islanded system. The 

prices for alternative work shall be set out in the same manner 

as for the work specified. 

DELIVERY TIMES

The Equipment Supplier shall provide the delivery times from receipt of order until 

the HVDC converter stations or AC substations are brought into commercial 

operation. 

EVIDENCE OF EQUIPMENT SUPPLIER’S ABILITY, EXPERIENCE AND PLANT

The Equipment Supplier is invited to provide evidence of ability and experience to 

supply the HVDC Converter stations and AC substations as requested. In particular 

experience with undersea cable systems and wind farms should be highlighted. The 

Equipment supplier shall include experience in providing HVDC and HVAC 
- 89 -

transmission as a sole radial feeder for wind turbines, their ratings, year of installation, 

Owner’s contact name, phone number and email address.

WARRANTIES

The Equipment Supplier is invited to provide a written description of the performance 

and equipment warranties that would be offered, including budget prices. 

OPERATION & MAINTENANCE SERVICE CONTRACTS

The Equipment Supplier is invited to provide a description of the O&M Service 

Contracts they could offer, assuming four such converter or substations are to be 

serviced. Two stations are to be located at different sites on Oahu, and one each on 

Molokai and Lanai. Budget servicing rates are to be supplied.

TECHNICAL DATA REQUESTS 

HVDC LINE OPERATION DURING SYSTEM FAULTS

The Equipment Supplier shall confirm the capability of the converters and AC 

substation equipment to operate within at least the low voltage and high voltage ride 

through characteristics of Figure 1 for the purposes of this investigation. The actual 

requirements may vary. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

Time (s)

Voltage (p.u.)

Normal Operating Limits

No Trip Zone

Emergency Voltage Boundaries
- 90 -

Figure 1: Undervoltage and overvoltage ride through characteristic 

 The Equipment Supplier shall confirm the capability of the converters and AC 

substation equipment to operate within at least the ac system frequencies as specified 

in Figure 2 for the purpose of this investigation. The actual requirements may vary. 

Figure 2: Operating frequency range of converter and substation equipment 

LOSSES

The following total losses for each of the HVDC Converter Stations and AC 

substation and equipment are to be supplied according to the loading level as 

indicated: 

Losses at 10 % rated power ______________ kW 

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

0 1 2 3 4 5 6 7 8 9 10

Time (s)

Hz

No Trip Zone

63 Hz

56 Hz for 6 sec

61.5 Hz

57 Hz
- 91 -

Losses at 50 % rated power ______________ kW 

Losses at 100% rated power ______________ kW 

RELIABILITY

The Equipment Supplier shall provide the expected reliability of each of the HVDC 

Converter Stations and AC substations, considering that there will be an HVDC 

Converter Station or AC Substation at each end of one circuit of an undersea cable.

The reliability is to be estimated based on having a spare transformer or spare 

transformer phase (if comprised of single phase units) that can be put into service 

within 5 days. Similarly, the estimate of reliability should include the impact of shunt 

reactors for the AC options where replacement of a faulted phase must be replaced 

within two days. 

Table 1: Calculated availability and reliability (HVDC/AC cables excluded)

HVDC CONVERTER VALVES

The Equipment Supplier shall provide the following information regarding the 

converter valves and associated equipment: 

Table 2: Converter valve design 

Type of solid state switching device __________________ 

Converter configuration (no. of levels, MMC, etc.) __________________ 

Continuous rating of total converter MW __________________ 

Rated direct voltage of each converter unit (150 kV kV __________________ 

Required) 

Rated direct current of each converter unit amps __________________ 

Number of converter units in total converter (one end) __________________ 

Maximum continuous overload current at low 

ambient temperature amps __________________ 

Phase or valve inductor per phase or bridge arm 

for each Converter Unit mH _________________ 

Failure Rate of one pair of HVDC Converter Stations/AC Substations ( at each 

end of one set of cables for one circuit ) in outages/year

HVDC Converter Stations/AC Substations Forced Energy Unavailability 

(FEU) ( at each end of one set of cables for one circuit )

HVDC Converter Station/AC Substation availability, considering only scheduled 

maintenance requirements (at each end of one set of cables for one circuit)
- 92 -

 

Positive reactive power (capacitive) at the high 

voltage busbar at rated power and excluding 

what is generated by the ac filters MVAR _________________ 

Negative reactive power (inductive) at the high 

voltage busbar at rated power and excluding 

what is generated by the ac filters MVAR _________________ 

Total reactive power rating of ac filters of 

converter MVAR _________________ 

HVDC CONTROLS AND PROTECTION

The Equipment Supplier is to provide a description of the control and equipment 

strategy to accommodate a wind farm at the sending end. In addition, please provide a 

recommended strategy for control of AC voltage at ends taking into account there will 

be other equipments controlling AC voltage (wind turbine generators at one end and 

installed synchronous generators at the other end). The converters must be able to 

transmit power in both directions even though initially this may not be required. 

OCEAN PROFILE AND ISLAND CROSSINGS

Preliminary bathymetry and ocean surveys have been conducted by SOEST at the 

University of Hawaii. Graphical information on ocean profile, depth, coverage and 

seabed composition is included in this request. Though no preferred island route has 

been identified, information provided relate to crossings between the relevant islands 

of Oahu, Molokai, Lanai and Maui. 

ACCURACY OF BUDGET ESTIMATES

The anticipated accuracy of budget estimates shall be provided.
- 93 -

October22, 2009 

To: High voltage power cable suppliers

ABB (Each to be individually addressed)

Fujikura

 Nexans 

Prysmian

Sumitomo (J-Power)

OAHU WIND INTEGRATION AND TRANSMISSION STUDY (OWITS)

BUDGET PRICING OF INTER-ISLAND CABLE OPTIONS

The US Department of Energy through the National Renewable Energy Laboratory (NREL) 

invites you to respond to this request for budget pricing information on various options for 

HVDC and AC undersea electric power cable transmission from the Hawaiian Islands of 

Molokai, Lanai and Maui to Oahu. 

Return Information

Please return the completed budget pricing form (pages 7 to 17 below) to:

National Renewable Energy Laboratory

Attn: David Corbus, 

1617 Cole Boulevard

Golden, CO 80401-3393

USA

Email: David.Corbus@nrel.gov 

By November 20, 2009.

Confidentiality

The information received from NREL through this request is confidential and must be 

treated as such. Likewise, the recipient of this request will not have their name or 

association with the information submitted to NREL on the budget pricing form disclosed to 

anyone other than the team specifically assigned to evaluate this project.
- 94 -

Background to the Project

This request follows a similar request for budget pricing of HVDC converter station and AC 

substation options that have already been sent out to equipment suppliers. This request is 

in response to the Hawaii Clean Energy Initiative (HCEI), which is a multiyear initiative with 

the State of Hawaii. HCEI is to provide technical support to the State to meet a selfimposed goal of 70% clean energy use through renewables and efficiency in the electricity 

and transportation sector by the year 2030 (40% by renewables).

One of the driving forces for FY09/10 work is the signed agreement between the State and 

Hawaiian Electric Company (HECO), Inc. that includes a combined commitment of up to 100 

MW of on-island wind resources and up to 400 MW of wind on the Islands of Lanai and 

Molokai via an inter-island cable that would bring that wind energy to Oahu.

 

To support the HCEI and HECO efforts, the Oahu Wind Integration and Transmission Study 

(OWITS) study has been initiated. The goal of OWITS is to help stakeholders, with special 

emphasis on the utility and the state, to understand the costs and operating impacts of 

significant amounts of wind power on their island grids and to help them identify the 

technical requirements of and configuration for an undersea inter-island cable to transmit 

electricity from large wind and or solar systems from one island to another island.

The HECO system on Oahu is today an island system without inter-ties to neighboring 

islands. With potential for at least 100 MW of on-island wind generation, the impacts of 

additional wind variability and transient impacts on grid reliability due to connecting 

neighbor island wind all need to be carefully considered. 

It can be assumed that the HECO system will only be able to allow a 200 MW loss due to any 

single point of failure.

There is a number of cable routing options from the islands of Molokai, Lanai and Maui to 

Oahu. Six options are for HVDC cables at ±150 kV and a seventh option is for HVAC cables at 

230 kV. A description of each option is included with each request along with seabed 

information. With up-to-date cable and termination pricing, it will be possible to select a 

preferred configuration for the interconnections. The HVDC options will be with Voltage 

Sourced Converters (VSC) which will allow solid XLPE type cable to be applied.

The connections from Molokai and Lanai to Oahu can be considered as a first stage 

development and can be scheduled to be placed in service in a practical sequence. A future 

interconnection from Maui to Oahu is a second stage development that does not require 

costs at this stage. Possible landing points for the cables are shown in Figure 1.
- 95 -

Figure 1: Possible cable landing points on the Hawaiian Islands.

Budget Pricing Requirements

Budget pricing is required for seabed survey, cable design, manufacture, transportation, 

laying, splicing, burying in the sea bed where required, horizontal directional drilling to an 

on-shore transition station and a 1 km underground cable installation to an HVDC converter 

station (or AC substation). Necessary cable accessories are to be included in the cable 

budget prices along with inclusion of normally supplied spares for such application. 

The budget prices are to be submitted as if they were being quoted for immediate 

installation of all stages, and are to be submitted in current US dollars.

Permitting and licensing costs are not to be included in the budget prices submitted. 

The connection to the receiving end of the interconnections on Oahu will be the HECO 

system.

Cable Options 

The HVDC cables will be for operation with voltage sourced converters at ±150 kV. AC cable 

options are being considered for 230 kV. Budget prices for the HVDC converter stations and 

AC substations are being requested separately. Climate is considered tropical.

Cable Burying

It is required that the cable be buried along its full length to depths appropriate to the 

composition of the seabed and to protect it against fishing, ships anchors and marine life, 

yet allow recovery for repairs if so needed.

For the approach to the southern shore of Oahu and designated as “Pearl” in the seabed 

information (since the cable will enter Pearl Harbor for this landing site), there is 

Kaneohe

Pearl
- 96 -

considerable dumped military equipment and ordinance on the seabed. This extends for a 

distance of approximately 6 miles (10 km) offshore. Careful survey will be required to 

determine a suitable route into Pearl Harbor.

No cable laying activity will be permitted for six months each year through the whale 

sanctuary (see Figure 2).

Figure 2: Humpback whale sanctuary

Existing Cables

There are existing telecommunication cables shown in red in Figure 3 that will be crossed by 

the power cables. The budget price request for the various power cable options to Oahu 

must include additional costs incurred when the power cables cross the existing 

telecommunication cables.

Penguin Bank
- 97 -

Figure 3: Locations of existing telecommunication cables

DC Cable Options

There are two landing sites on Oahu for the cables from Molokai and Lanai. The south shore 

landing site is Pearl, and the west shore landing is Kaneohe (see Figure 1). The DC cable 

options for which budget prices are required are for ±150 kV for bipole or symmetrical 

monopole converter station configuration and are listed as follows:

DC Cable Option 1: Molokai to Kaneohe, three cables 60 km long, two rated at 150 kV and 

1,333 amps and the third at 50 kV and 1,333 A as a metallic return. 

Figure 4: DC Cable Option 1

200 MW 400 MW 

200 MW Molokai 

Kaneohe 400 MW Bipole 
- 98 -

DC Cable Option 2: Molokai to Pearl, three cables 87 km long, two rated at 150 kV and 1,333 

amps and the third at 50 kV and 1,333 A as a metallic return.

Figure 5: DC Cable Option 2

DC Cable Option 3: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Molokai to Pearl, two cables 87 km long each rated at 150 kV and 667 amps. 

Figure 6: DC Cable Option 3

DC Cable Option 4: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Lanai to Pearl, two cables 126 km long with one rated at 150 kV and 1,333 amps 

and the other as a metallic return cable rated at 50 kV and 1,333 amps. Molokai to Pearl, 

two cables 64 km long each rated at 150 kV and 667 amps. The pole configuration between 

Lanai and Pearl is to accommodate a future second stage polar extension to Maui.

Figure 7: DC Cable Option 4

400 MW

Pearl

Molokai

400 MW Bipole 

400 MW

Molokai

Kaneohe

Pearl 

200 MW Symmetrical Monopole

200 MW Symmetrical Monopole

200 MW

Kaneohe Molokai

Pearl 

200 MW Symmetrical Monopole

200 MW Pole

Lanai 

200MW Symmetrical 

Monopole between Lanai 

and Molokai 
- 99 -

DC Cable Option 5: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Lanai to Kaneohe, two cables 120 km long each rated at 150 kV and 667 amps.

Figure 8: DC Cable Option 5

DC Cable Option 6: Molokai to Pearl, two cables 87 km long each rated at 150 kV and 667 

amps. Lanei to Pearl, two cables 126 km long with each rated at 150 kV and 667 amps.

Figure 9: DC Cable Option 6

Molokai

Lanai 

2 - 200 MW Symmetrical 

Monopoles 

200 MW

200 MW

Kaneohe

200 MW 

Pearl 

Molokai

200 MW Symmetrical 

Monopole 

Lanai

200 MW 

200 MW Symmetrical 

Monopole 
- 100 -

AC Cable Option

One ac cable option is under investigation. Each ac cable can be either three single core, 

XLPE coaxial cables laid in trefoil formation or one three core XLPE cable.

AC Cable Option: Molokai to Kaneohe, one three phase circuit 60 km long rated at 230 kV 

and 650 amps rms. Lanai to Pearl, one three phase circuit 126 km long rated at 230 kV and 

700 amps rms.

Figure 10: AC Cable Option

Seabed Assessment

A preliminary seabed assessment is available for the proposed power cable routes between 

Oahu, Molokai and Lanai. These are presented as follows:

Kaneohe to Molokai

This route is 60 kilometers long, with approximately 15-18 kilometers shallower than 125 

meters, mostly living and relict coral, at the landward ends, each of which dips gently 

seaward over about 8 kilometers. The central 35 kilometers or so lies deeper than 600 

meters, approaching a maximum depth of 800 meters, and this section is relatively flat at a 

broad scale. It is likely that much of this is sandy mud, although there will be blocks of coral 

rubble that has slid from both marginal platforms based. Conservatively, it is estimated that 

there may be 20 kilometers of soft sediment and 15 kilometers of rubble here. The slopes 

on each side will also have significant amounts of course debris and rubble shed from the 

reefs above them and some in situ reef outcrops that have been drowned by island 

subsidence. There was difficulty getting penetration or significant recovery with a corer on 

either margin, thus it is estimated the slope to be between 125 and 600 meters consolidated 

sand and carbonate rubble/outcrops.

Summary, Kaneohe to Molokai: Living/relict reef: 20 kilometers. Consolidated sand and 

rubble: 20 kilometers. Unconsolidated sandy mud: 20 kilometers. See Figures 11 and 12.

200 MW

Molokai

Lanai

200 MW 

Pearl

Kaneohe

1 three phase 230 kV AC Cable 

1 three phase 230 kV AC Cable
- 101 -

Figure 11: Route for Kaneohe to Molokai cables

Figure 12: Bathymetric data for the cable route between Kaneohe and Molokai.

Kaneohe to Lanai

The initial 60 kilometers of this route is identical to that above, from Kaneohe to NW 

Molokai, thus the sediment types are the same. The remaining 64 kilometers from Ilio Point 

on the NW corner of Molokai to the Lanai landing site, is mainly in water shallower than 100 

meters, mostly 50 to 100 meters, and thus a mixture of living and dead reef and carbonate 

sands. Approximately 20 kilometers lies deeper than 125 meters, to a maximum depth of 

about 275 meters. This route is also swept by fast currents, and most fine grained material 
- 102 -

is swept away except in the lee of obstacles. It would be reasonable to assume that most of 

it is consolidated sand and rubble.

Summary, Kaneohe to Lanai: (including estimates above for Kaneohe to Molokai):

Living/dead reef: 64 kilometers. Consolidated sand and rubble: 40 kilometers. 

Unconsolidated sandy mud: 20 kilometers. See Figures 13 and 14.

Figure 13: Route for Kaneohe to Lanai cables
- 103 -

 

Figure 14: Bathymetric data for the cable route between Kaneohe and Lanai.

Pearl Harbor to Lanai

This route is 126 km long. It begins with a nominal five kilometers in the dredged channel 

entering Pearl Harbor, assumed here to be hard ground dredged through living and dead 

reef. There is an additional 25 kilometers of less than 125 meters depth, including the 

section crossing the northern end of Penguin Bank, considered mostly to be living reef and 

carbonate sand, and the approach to the Lanai landing. The central channel region between 

Oahu and Penguin Bank includes about 55 kilometers deeper than 500 meters, deepest 

point slightly less than 700 meters, of which it is estimated that 35 kilometers is likely soft, 

unconsolidated sandy mud, and 20 kilometers, particularly along the base of Penguin Bank, 

is rubble and coarse debris shed from the bank with some reef outcrops predating island 

subsidence. There is 25 kilometers along the slope south of Molokai and crossing the 

channel between Molokai and Lanai, where depths range between 125 and 300 meters; as 

in previous sections, this current-swept region is mainly consolidated sand and coarse 

material, including reef debris. Of the remaining 16 kilometers, on the slopes south of Oahu 

and rising up Penguin Bank, it is estimated that perhaps 5 kilometers is soft unconsolidated 

sandy muds, while the remaining 11 kilometers is rubble or hard outcrops, particularly on 

the slope of Penguin Bank.

Summary Pearl Harbor to Lanai: 30 kilometers of living/dead reef. 56 kilometers of 

consolidated sand and rubble. 40 kilometers of unconsolidated sandy muds. Up to ten 

kilometers of the route, mostly across unconsolidated sediment south of Pearl and Honolulu 

Harbors, contains discarded munitions and other anthropogenic debris, some potentially 

quite hazardous. See Figures 15 and 16.
- 104 -

Figure 15: Route for Pearl to Lanai cables

Figure 16: Bathymetric data for the cable route between Pearl and Lanai.

Pearl Harbor to Molokai

This 87 kilometer route is the same as Pearl Harbor to Lanai for the first ~70 kilometers, 

then heads northeast up the slope to Ilio Point on the northwest corner of Molokai. The 

eastern portion is largely the western slope of Molokai and the approach to Ilio Point, 

neither of which is expected to have more than nominal amounts of unconsolidated 

sediment. It is infered that most of the new stretch here on the approach to Molokai is 

consolidated sand and rubble, with 1-2 kilometers of living reef at the top of the slope. 

Summary, Pearl Harbor to NW Molokai: 7 kilometers of living/dead reef. 40 kilometers of 

consolidated sand and rubble. 40 kilometers of unconsolidated sandy muds. Up to ten 

kilometers of the route, mostly across unconsolidated sediment of Pearl and Honolulu 
- 105 -

Harbors, contain discarded munitions and other anthropogenic debris, some potentially 

quite hazardous. See Figures 17 and 18.

Figure 17: Route for Pearl to Molokai cables
- 106 -

Figure 18: Bathymetric data for the cable route between Pearl and Molokai.

Molokai to Lanai

The 64 kilometers from Molokai to the Lanai landing site, is mainly in water shallower than 

100 meters, mostly 50 to 100 meters, and thus a mixture of living and dead reef and 

carbonate sands. Approximately 20 kilometers lies deeper than 125 meters, to a maximum 

depth of about 275 meters. This route is swept by fast currents, and most fine grained 

material is swept away except in the lee of obstacles. It would be reasonable to assume that 

most of it is consolidated sand and rubble.

Summary, Molokai to Lanai: Living/dead reef - 64 kilometers. See Figures 19 and 20.
- 107 -

Figure 19: Route for Molokai to Lanai cables
- 108 -

Figure 20: Bathymetric data for the cable route between Molokai and Lanai
- 109 -

CABLE SUPPLIER'S NAME 

 

Project: Oahu Wind Integration and Transmission Study (OWITS)

HVDC and AC Undersea Cables

CABLE BUDGET PRICING FORM

PRICING 

Firm lump sum prices are to be provided for to all labor, materials, equipment, required 

spares that includes seabed survey, cable design, manufacture, transportation, laying, 

splicing, burying in the sea bed, horizontal directional drilling to an on-shore transition 

station and a 1 km underground cable installation to an HVDC converter station (or AC 

substation), and testing and commissioning of the HVDC and AC cable options. 

For the purpose of evaluation the budget price shall be broken down as follows:

DC Cable Option 1: Molokai to Kaneohe, three cables 60 km long, two rated at 150 kV and 

1,333 amps and the third at 50 kV and 1,333 A as a metallic return. 

1. Basic cable cost $___________________ 

 2. Seabed survey $___________________ 

 3. Laying and burial of cable $___________________ 

 4. HDD, and termination 1 km from shore (both ends) $___________________ 

 5. Duty, based on a _____% rate $___________________ 

 6. Insurance $___________________ 

 7. Total $___________________

Additional information for DC Cable Option 1

 8. Time from order to in-service Months _____________ 

 9. Losses in HV cable at rated voltage and current MW______________ 

 10. Losses in HV cable at rated voltage and no load MW ______________ 

 11. 30 minute current overload rating Amps_____________ 
- 110 -

12. Please provide Catalog numbers of each cable and copy of catalog information 

including weight/m, cross-sectional dimensions and materials 

13. Please provide recommended burial depths in the seabed. 

DC Cable Option 2: Molokai to Pearl, three cables 87 km long, two rated at 150 kV and 1,333 

amps and the third at 50 kV and 1,333 A as a metallic return.

1. Basic cable cost $___________________

2. Seabed survey $___________________

3. Laying and burial of cable $___________________

4. HDD, and termination 1 km from shore (both ends) $___________________

5. Duty, based on a _____% rate $___________________

6. Insurance $___________________

7. Total $___________________

Additional information for DC Cable Option 2 

 8. Time from order to in-service Months _____________

9. Losses in HV cable at rated voltage and current MW______________

10. Losses in HV cable at rated voltage and no load MW ______________

 11. 30 minute current overload rating Amps_____________

12. Please provide Catalog numbers of each cable and copy of catalog 

information including weight/m, cross-sectional dimensions and material. 

13. Please provide recommended burial depths in the seabed. 

DC Cable Option 3: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Molokai to Pearl, two cables 87 km long each rated at 150 kV and 667 amps. 

1. Basic cable cost $___________________

2. Seabed survey $___________________

3. Laying and burial of cable $___________________

4. HDD, and termination 1 km from shore (both ends) $___________________

5. Duty, based on a _____% rate $___________________

6. Insurance $___________________

7. Total $___________________
- 111 -

Additional information for DC Cable Option 3 

 8. Time from order to in-service Months _____________

9. Losses in HV cable at rated voltage and current MW______________

10. Losses in HV cable at rated voltage and no load MW ______________

 11. 30 minute current overload rating Amps_____________

12. Please provide Catalog numbers of each cable and copy of catalog 

information including weight/m, cross-sectional dimensions and material 

13. Please provide recommended burial depths in the seabed. 

DC Cable Option 4: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Lanai to Pearl, two cables 126 km long with one rated at 150 kV and 1,333 amps 

and the other as a metallic return cable rated at 50 kV and 1,333 amps. Molokai to Pearl, 

two cables 64 km long each rated at 150 kV and 667 amps. The pole configuration between 

Lanai and Pearl is to accommodate a future second stage polar extension to Maui. 

1. Basic cable cost $___________________

2. Seabed survey $___________________

3. Laying and burial of cable $___________________

4. HDD, and termination 1 km from shore (both ends) $___________________

5. Duty, based on a _____% rate $___________________

6. Insurance $___________________

7. Total $___________________

Additional information for DC Cable Option 4

 8. Time from order to in-service Months _____________

 9. Losses in HV cable at rated voltage and current MW______________

10. Losses in HV cable at rated voltage and no load MW ______________

 11. 30 minute current overload rating Amps_____________

12. Please provide Catalog numbers of each cable and copy of catalog 

information including weight/m, cross-sectional dimensions and material. 

13. Please provide recommended burial depths in the seabed. 
- 112 -

DC Cable Option 5: Molokai to Kaneohe, two cables 60 km long each rated at 150 kV and 

667 amps. Lanai to Kaneohe, two cables 120 km long each rated at 150 kV and 667 amps. 

1. Basic cable cost $___________________

2. Seabed survey $___________________

3. Laying and burial of cable $___________________

4. HDD, and termination 1 km from shore (both ends) $___________________

5. Duty, based on a _____% rate $___________________

6. Insurance $___________________

7. Total $___________________

Additional information for DC Cable Option 5 

 8. Time from order to in-service Months _____________

 9. Losses in HV cable at rated voltage and current MW______________

10. Losses in HV cable at rated voltage and no load MW ______________

 11. 30 minute current overload rating Amps_____________

12. Please provide Catalog numbers of each cable and copy of catalog 

information including weight/m, cross-sectional dimensions and materials

13. Please provide recommended burial depths in the seabed. 

DC Cable Option 6: Molokai to Pearl, two cables 87 km long each rated at 150 kV and 667 

amps. Lanei to Pearl, two cables 126 km long with each rated at 150 kV and 667 amps. 

1. Basic cable cost $___________________

2. Seabed survey $___________________

3. Laying and burial of cable $___________________

4. HDD, and termination 1 km from shore (both ends) $___________________

5. Duty, based on a _____% rate $___________________

6. Insurance $___________________

7. Total $___________________

Additional information for DC Cable Option 6 

8. Time from order to in-service Months _____________
- 113 -

 9. Losses in HV cable at rated voltage and current MW______________

10. Losses in HV cable at rated voltage and no load MW ______________

11. 30 minute current overload rating Amps_____________

12. Please provide Catalog numbers of each cable and copy of catalog 

information including weight/m, cross-sectional dimensions and material 

13. Please provide recommended burial depths in the seabed. 

AC Cable Option: Molokai to Kaneohe, one three phase circuit 60 km long rated at 230 kV 

and 650 amps rms. Lanai to Pearl, one three phase circuit 126 km long rated at 230 kV and 

700 amps rms. 

1. Basic cable cost $___________________ 

 2. Seabed survey $___________________ 

 3. Laying and burial of cable $___________________ 

 4. HDD, and termination 1 km from shore (both ends) $___________________ 

 5. Duty, based on a _____% rate $___________________ 

 6. Insurance $___________________ 

 7. Total $___________________

Additional information for AC Cable Option

 7. Time from order to in-service Months _____________ 

 8. Losses/phase at rated voltage and current MW______________ 

 9. Losses/phase at rated voltage and no load MW ______________ 

 10. 30 minute current overload rating Amps_____________ 

11. Please provide Catalog numbers of each cable and copy of catalog information 

including weight/m, cross-sectional dimensions and materials 

12 Please provide recommended burial depths in the seabed. 

OFFER OF ALTERNATIVES

The Cable Supplier shall provide budget prices on the work 

exactly as requested. However, the Cable Supplier is invited to 
- 114 -

offer alternatives. If an alternative is offered, the Cable 

Supplier shall state clearly in what way the alternative differs 

from what has been requested, why such alternative work is 

offered. The prices for alternative work shall be set out in the 

same manner as for the work specified. 

DELIVERY TIMES

The Cable Supplier shall provide the delivery times from receipt of order until the 

cables have been tested and commissioned and made available for commercial 

operation. 

EVIDENCE OF CABLE SUPPLIER’S ABILITY, EXPERIENCE AND PLANT

The Cable Supplier is invited to provide evidence of ability and experience to supply 

the HVDC and AC cables as requested. The Cable Supplier shall include experience 

in providing HVDC and HVAC undersea cables as requested herein including their 

ratings, year of installation, Owner’s contact name, phone number and email address.

WARRANTIES

The Cable Supplier is invited to provide a written description of the performance and 

equipment warranties that would be offered, including budget prices. 

OPERATION & MAINTENANCE SERVICE CONTRACTS

The Cable Supplier is invited to provide a description of the O&M Service Contracts 

they could offer. Budget servicing rates are to be supplied. 

REPAIR

The Cable Supplier shall provide the expected repair time it will take after a cable 

fault has occurred. Note, that for a period of six months each year no repair activity 

may be possible due to whales resident in the whale sanctuary (See Figure 2).

ACCURACY OF BUDGET ESTIMATES

The anticipated accuracy of budget estimates shall be provided.
F1146-E(10/2008) 

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

February 2011

2. REPORT TYPE

Subcontract Report

3. DATES COVERED (From - To)

2008 - 2011

4. TITLE AND SUBTITLE

Oahu Wind Integration and Transmission Study (OWITS): Hawaiian 

Islands Transmission Interconnection Project

5a. CONTRACT NUMBER

DE-AC36-08GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Dennis Woodford

5d. PROJECT NUMBER

NREL/SR-5500-50411 

5e. TASK NUMBER

SS101362

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Electranix Corporation

12 – 75 Scurfield Blvd

Winnipeg, Manitoba R3Y 1G4 Canada

8. PERFORMING ORGANIZATION

REPORT NUMBER

LAM-9-99436-01

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

NREL/SR-5500-50411 

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161

13. SUPPLEMENTARY NOTES

NREL Technical Monitor: David Corbus

14. ABSTRACT (Maximum 200 Words)

This report provides an independent review included an initial evaluation of the technical configuration and capital 

costs of establishing an undersea cable system and examining impacts to the existing electric transmission systems 

as a result of interconnecting the islands.

15. SUBJECT TERMS

undersea cable; Maui; Lanai; Molokai; Hawaii Clean Energy Agreement; grid integration; operational impacts, 

transmission planning; Electranix; XLPE cable; voltage sourced converters

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT

UL

18. NUMBER 

OF PAGES

19a. NAME OF RESPONSIBLE PERSON

a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified 19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98)

Prescribed by ANSI Std. Z39.18