JPL Publication 86-41 DOElET 29372-6 

Distribution Category UC-97b 

Distribution Sys tem 

Simulator 

K. A. Bahrami 

H. Kirkham 

S. Rahman 

(HASA-CB-1799 18) DISTRIBUTICN SYSTEEl N87-11940 

SlHULA'IOB [Jet PrcFulsicn lac,) 44 p 

CSCL 090 

uric Id 5 

63/33 44934 

August 

/ 

5, 1986 

Prepared for 

U.S. Department of Energy 

Through an Agreement with . National Aeronautics and Space Administration 

by 

Jet Propulsion Laboratory 

California institute of Technology 

Pasadena, California 

\ 
JPL Publication 86-41 

Distribution System 

Simulator 

K. A. Bahrami 

H. Kirkham 

S. Rahman 

August 15, 1986 

Prepared for 

U.S. Department of Energy 

Through an Agreement with 

National Aeronautics and Space Administration 

Jet Propulsion Laboratory 

California Institute of Technology 

Pasadena. California 

by 

DOElET 29372-6 

Distribution Category UC-97b 
This work was performed for the Jet Propulsion Laboratory, California 

Institute of Technology, and was sponsored by the Electric Energy Systems 

Division of the U.S. Department of Energy through an agreement with the 

National Aeronautics and Space Administration. 

This report was prepared as an account of work sponsored by an agency of the 

United States Government. Neither the United States Government nor any agency 

thereof, nor my of their employees, makes any warranty, express or implied, 

or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process 

disclosed, or represents that its use would not infringe privately owned 

rights. 

Reference heroin to any specific commercial product, process, or service by 

trade name, trademark, manufacturer, or otherwise, does not necessarily 

constitute or imply its endorsement, xecommendation, or favoring by the United 

States Government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United 

States Government or any agency thereof. 

ii 
ABSTPACT 

In a series of tests performed under Department of Energy auspices, power line 

carrier propagation was observed to be anomalous under certain circumstances. 

To investigate the cause, a distribution system simulator was constructed. 

The simulator was a physical simulator that accurately represented the 

distribution system from below power frequency to above 50 kEz. Effects such 

as phase-to-phase coupling and skin effect were modeled. 

Construction details of the simulator, ad experimental results from its use 

are given in this report. 
In 1976 the Energy Research and Development Administration (EWA), now the 

US Department of Baergy (Doe) was supporting the concept of load management 

(using a number of systems to communicate between control centers and control 

points) for energy conservation in utility distribution systems. Several 

methods were considered to satisfy communication requirements for load 

management: Power Line Carrier (ac), ripple, radio, and telephone. 

While the approaches were far from new, the technology as applied to load 

management in the utility distribution systems was relatively immature. To 

alleviate this situation, several projects were supported by industry, To 

contribute to the technology of PLC and ripple, two research projects were 

sponsored by EIUU: 

(1) Radio Frequency (BPI Model of the Distribution System as a 

Communication Channel, (referred to in this report as the RF Model). 

(2) A Noise Analysis of the Distribution System. 

To encourage industry to enter the market and to get experience with the 

characteristics of the various systems, PBM and the Electric Power Research 

Institute (€MU) entered into a jointly sponsored program, Demonstrations of 

Commuuication Systems for Distribution Automation lhese demonstrations 

consisted of the following systems and sponsors: 

(1) PLC systems: 

(a) EPRI/Detroit Edison/Westinghouse. 

(b) EPUI/Carolina Pmer and Light (CP&L)/Compugoatd. 

(c) ERDA(DOE)/Oak Ridge National Laboratory(0RNL) / 

San Diego Gas and Electric (SDG&E)/American Science and 

Ehgineering (As&&). 

(2) Radio systems: EPRI/hg Island Lighting Co. (LZMX))/Westinghouse. 

(3) Telephone systems: ERDA(we)/oBNL/omOha Public Power District/ 

Metropolitan Utili ties District/Darco. 

These Programs ran more or less concurrently. 

Certain aspects of the PLC systems contributed to the need for a Distribution 

System Simulator. Early in the course of the demonstrations, problems in the 

iv 
performance of all of the PLC systems were encountered. For the communication 

aspects of the problems, these were probably caused by the following factors: 

(1) Immature extension to the distribution system of trausmission line 

PLC technology, urge to enter the market quickly before the 

compo ti tion. 

(2) Development on small distribution systems and subsequent application 

t o l u g e distribution systems. 

(3) Extreme changes in line impedance and the need for line preparation 

(4) Lack of understanding of injection techniques. 

(5) Eigher than expected line noise. 

(6) Poor implaantation 

(7) Lnr carrier powers. 

(8) Frequency selection. 

(9) Failures. 

The simulator described in this report was developed as part of the work of 

the Communications and Control Project at the Jet Propulsion Laboratory, 

primarily through the efforts of the then Project Manager, Carl Gilchriest. 

Its purpose was to provide a better understanding of the exact nature of the 

problems experienced with the PLC systems. To provide verifiable results, the 

simulator was designed to model a section of the distribution system of the 

SDG E Company. Flexibility was provided so that the effect of changing 

parame tors could be ascertained. 

This report, based largely on the work of Carl Gilchriest, describes the 

design and construction of the Power System Simulator and discusses some of 

the results obtained from it. One of the authors, S Bahman, is at Virginia 

Polytechnic Institute and State University. 

V 
IN'IRODUCTION AND BACKGROUND ...................... 1-1 

Background .............................. 1-1 

Simulation by Digital Computer .................... 1-1 

Analog versus Digital Simulation ................... 1-3 

Simulator Constructed ........................ 1-3 

Feeder Topology ............................ 1-7 

Overhead Line Configuration ...................... 1-7 

UTBEMATICS OF TBANSFORMER SCALING .................. 2-1 

Introduction and Purpose ....................... 2-1 

Scaling ................................ 2-1 

Summary ................................ 2-6 

BARDWAREDESCRIPTION ......................... 3-1 

Substation Simulator ......................... 3-1 

Feeder Simulator ........................... 3-1 

Other Eardware ............................ 3-4 

SAN DIEGO GAS AND ELECTRIC STUDY ................... 4-1 

Introduction and Purpose ....................... 4-1 

Laboratory Verification Tests ..................... 4-10 

Field Measurements .......................... 4-13 

Conclusions .............................. 4-15 

h81ySiS ............................... 4-1 

SUMMARY AND CONCLUSIONS ........................ 5-1 

FIGURES 

1-1 . Distribution System Simulator ................ 1-4 

1.2 . Close-up of Feeder Simulator Simulating a Radial 

Distribution System .................... 1-5 

3.1 . Schematic of the Substation Simulator ............ 3-2 

3.2 . Primary Phase-to-Ground Current Injection on 

PhaseA ........................... 3-4 

3.3 . Schematic of Feeder Simulator Shoring Various 

Sections., ........................ 3-5 

3.4 . Layout of Each Unit in a Unit Pair ............. 3-6 

4.1 . Substation Bus Load Admittances .............. 4-2 

4.2 . Primary Phase-to-Ground Current Injection Method 

onPhase1 ......................... 4-7 

4.3 . Primary Phase-to-Phase Current Injection Method 

on Phases 1 and 2 ..................... 4-7 

vii 
2.1 . Summary of Values and Scaled Values for the SDG&& 

Murray Substation Transformers ............... 2-5 

3.1 . Values for the SDGLE Murray Substation Transformers ..... 3-3 

3.2 . Feeder Simulator Section Characteristics .......... 3-7 

4.1 . Summary of Analysis ..................... 4-11 

4.2 . Summary of Calculations and Laboratory 

Verification ........................ 4-12 

4.3 . Murray Substation North PLC Bus Voltage Measurements 

Made by AS&E (Reformatted to Correspond to 

Tables 4-1 and 4.2) ..................... 4-13 

viii 
SECrIoN I 

I"IX0DU~ION AND BACKGPOOND 

Background 

Because Power ine Carrier (PLc) systems use equipment w-ich is wholly owned 

by the Electric Utility, they have been viewed favorably for distribution 

system communications, PLC systems suffer from the disadvantage that the 

communications channel is primarily a power transmission system and not a 

communications medium. The principal problem encountered because of this is 

noire: the electric power system itself or rather the loads on the power 

system, during normal operation, generate a considerable amount of noise. 

Conventional methods of reducing the impact of power system noise on PLC 

communications systems include reducing the data rate and increasing the 

injected power. Both of these approaches were used in a series of 

demonstrations performed under Energy Research d Development Agency (MUM) 

and Department of Energy (Doe) auspices in the late 1970s. 

In spite of this, problems were experienced with the PLC systems at a number 

of the locations in these demonstrations. The problems were such that 

communications were breaking down over power line distances, which should, .in 

principle at least, have been achievabla 

Simulation by Digital Computer 

It was difficult to determine the exact cause of the problems in the field. 

Generally speaking, field tests have the following disadvantages: 

(1) Isolation of cause and effect is difficult to achieve. 

(2) Parameters are timevariant. 

(3) Field crews are expensive, and safety is a problan. 

(4) Field tests are weather dependent. 

(5) The accuracy of field tests is difficult to maintain. 

Simulation provides a more convenient means of investigation. A number of 

different simulation methods were used to address the PLC problem. 

Om of the fundamental tools developed to aid in the solution of some of these 

problems was a sophisticated computer radio frequency (BPI model of the 

distribution system. The RF model is capable of analyzing the impdances and 

signal levels of the distribution system and of obtaining the resulting signal 

levels at any point in the distribution network. This model, called the RF 

Model of the Distribution System as a Communication Channel, was developed 

under contract with the General Electric Company (GE) Research Center in 

Schenectady, New Pork. 

1-1 
While this computer model was a useful tool in analyzing the distribution 

networks for PLC propagation, it was not readily accepted by the utilities for 

various reasons: 

Detailed data that were frequently difficult to accumulate were 

required to exercise the computer program. Collection of the data 

required a different style of labor than utility distribution 

engineers were accustomed to supplying. When the time and cost of 

analyzing all distribution ne tworks were considered, the 

distribution engineers were overwhelmed. 

The computer model involved a complicated program that required a 

considerable amount of expertise to operate and keep current. 

Operator training was expensive and had to be kept current to be 

effective. If the contract was not continuous, operators and 

programmers drifted to other work and were not available if 

modifications were required. 

The computer model was developed around one specific computing 

system that was not universally available. Transportability to 

other computers and raverif ication would have been expensive. 

There was one essential proprietary subprogram in the computer model 

that was not generally available to other companies. 

The computer program was time consuming to modify if something new 

were required of it. 

GE, a company involved in sales of PLC systems, did not show 

interest in providing the computer semice to other manufacturers. 

GE had, however, provided the service to utilities. 

Ihe BF Model was verified by GE on the Niagara Muhawk Power Co., Schenectady, 

New York, and proved to be useful up to 50 kEz. A great deal of confidence in 

the ability to calculate signal levels, etc., has been achieved. Good 

correspondence with measured values has also been achieved. 

Problems were encountered in getting PLC communications through certain 

feeders of the Hurray Substation of the San Diego Gas and Electric Co. 

(SIXi&e) for the I3tDA/(DOE)/OBNWSDG&E/AS&E system. Signals were almost zero 

near one specific feeder junction lhe computer model at Schenectady, New 

York, was exercised from the Jet Propulsion Laboratory (JPL), Pasadena, 

California, by telephone line. Data representing the SDG&E system were used. 

With this simulation, the problem at the junction was determined to be caused 

by a lateral that had a short section of overhead wire feeding a long section 

of underground wire. The overhead wire was highly inductive, and the 

undergrouud wire was highly capacitive at the operating frequency. lhese 

components were series resonant, which caused an impedance transformation that 

resulted in a very low impedance at the junction. From this analysis, a 

modification was devised. Power factor correction capacitors and inductors 

were installed, which essentially formed a parallel resonant circuit with the 

offending underground cable. Subsequent communications tests with this 

modification were successful. 

1-2 
Analog versus Digital Simulation 

Some of the disadvantages of field tests have already been stated. There is 

also the question of analog versus digital simulation Some characteristics 

of analog and digital simulation include the following: 

Analog Simulation Qaracteristics: 

Analog simulators model the power system component by component. As 

a result, there is physical correspondence between the real and 

modelled systas. 

Superposition of ef fects applies. (This especially applies to 

assembly of harmonics for certain tasks.) 

Results are almost real time. 

Noise propagation studies are easier. 

Gbick reconfiguration is possible. (This depends on the hardware 

design. 1 

Ordinary instrumentation is available, 

To construct a simulator, it is necessary to have mathematical 

relationships describing each component. 

Safety is not a problem. 

Digital Simulation Characteristics: 

(1) Processing is generally mare accurate. 

(2) In addition to requiring a model of each component, as in (7) above, 

it is necessary to have mathematical relationships describing the 

entire system. This aspect is accomplished by hardware 

intercomctions in an analog simulator. 

(3) Programming knowledge is required. Expensive training is required. 

(4) Changes in output/input are more difficult. 

Simulator Coistrueted 

The Distribution System Simulator consists of two analog simulators: a 

substation and a feeder simulator (Figures 1-1 and 1-2). 

Substation Simulator 

During the testing on the threephase PLC system installed at SDG&E, currents 

were injected in six possible ways. (mere are three phasertwphase and three 

phase-twground possibilities.) The resulting voltages on the feeder buses 

were difficult to explain. JPL undertook the tasks of performing a 

mathematical analysis of the circuit and of assembling a substation analog to 

1-3 
ORIGINAL PAGE IS 

OF POOR QUACm 

.- 

”; 

Figure 1-1. Distribution System Sbulator 

1-4 
ORIGINAL PAGE Is 

OF POOR QUALm 

Figure 1-2. Close-up of Feeder Simulator Simulating a Radial Distribution Sgstenr 

1-5 
verify the analysis. The results of the tasks were in correspordence with one 

another and were successful in explaining the measured results at SDG&B. 

Ihe substation simulator was also used to check out other ideas, one of which 

was the design of a directional coupler capable of rejecting noise coming into 

the substation from different feeders. Theoretically, this circuit is capable 

of approximately 10-dB improvement in communications in a substation with 9 to 

11 feeders. The complete 

simulator ran into problems in scaling the drives from current transformers 

that modeled the substation switchgear. 

Bench checks were completed on parts of the system. 

Tests are still incomplete. 

Feeder Simulator 

The feeder simulator was considered as an alternate to augment the 

capabilities of the digital simulator. In addition to the reasons listed 

above for advantages of the analog simulator over the digital simulator for 

RC systems, it was also decided that the analog feeder simulator would be 

useful in the following studies: 

(1) Earmonic propagation studies of Dispersed Storage and Generation 

(DSGs) and similar hardware. 

(2) Stability studies of installed DsGs. 

(3) Transient network analysis (distribution system fusing studies, 

etc. 1. 

The following goals were established for the design of an analog feeder 

simulator: 

(1) Cover a frequency range of 60 to 50,000 Ez without changing 

parw ter values. 

(2) Simulate skin effect on wire resistance and inductance. 

(3) Simulate ground impedance. 

(4) Create a flexible design that can be easily changed to accommodate 

topology and parameter changes. 

(5) Create a design that has easy physical access to circuit points. 

(6) Place simulated line hardware within the equivalent of one-half city 

block of the true position of a real selected feeder. 

(7) Account for all interconductor inductances and capacitances. 

1-6 
The feeder simulator was successfully constructed. All design goals# with one 

exception, were met. The exception was that the performance of the simulator 

at extreme high frequency might not be the same as the distribution system. 

The frequency response of the interconductor inductance simulation and skin 

effect simulation was measured, as well as the impulse response of the feeder 

simulator. The remainder of the tests, including PZC propagation, .noise 

propagation, load effects, etc., were not completed. 

Feeder Topoloay 

It was the acigiarl intention to simulate SDG&E's Circuit 85 from their Murray 

Substation in El Cajon, California, because RLC cmmunication problems had 

been experienced on this circuit, and because considerable field tests and 

computer simulation had been accomplished to determine their cause. 

Circuit 85 was an excellent location for conducting any DSG experiment. 

Before the simulator could be completed, SDG&E decommissioned the RC trials 

and showed little interest in DSG for the future, BOIlwer, Circuit 85 was 

used as a guide in setting the simulator topology. 

The simulator uses discrete elements to simulate the distributed parameters of 

a multiconductor feeder. The section lengths to be simulated were selected on 

the basis of bow closely transformers and other hardware would be located. It 

was decided that these sections should be about one city block (or about 

100 m). These 100-0 sections could be assembled into almost any topology. 

Provisions were also made for changing of conductor sizes of #oooo, #OD #2, 

#4, and #6 solid round copper wire. A feeder of 8000 m in simulated length 

was subsequently constructed. 

Overhead Line Config~ration 

The overhead line configuration selected for simulation had three-phase wires 

and a neutral wire on a single cross arm. The wire spacing was 3 ft on 

centers and 42 ft above grouud. This configuration was typical of the express 

feeder on Circuit 85 at SDGWs Murray Substation but not necessarily typical 

of the entire feeder. Conductors on other cross arms were not considered. 

Tho wide spacings give small interconductor capacitance and large 

interconductor inductance, and give a slightly more extreme value of 

components for the simulator design. 

1-7 
SECTION XI 

WIUEUTICS OF TPANSFOBYBP SCALING 

Inttoduetion and Purpose 

The purpose of this section is to describe the transformer scaling used for a 

partial simulation of the DOE/OBNL/SDG&B/AS&E demonstration. The term 

scaling means that the value of some system parameter is changed, such as 

frequency, voltage, current, impedance, e tc., so that simula tion can be 

acoomplished at greater comenience (for example, smaller size, faster, less 

power, or greater/smaller frequency). 

It is inconvenient to duplicate the distribution system transformers 

(substation and distribution transformers) in the laboratory because of their 

size and size-related cost. The size is dictated by the power-handling 

capability of the transformers, and is not related to its communication system 

performance except with regard to how the powerhandling capability determines 

the impedance parameters of the transformer. It is the interplay of the 

system impedances that affects the communication system performance, and not 

60-E2 power levels. Although impedances can readily be scaled, it would seem 

desirable mt to scale impedances (and frequencies) so that results could be 

interpreted without resoaling. 

Soaling 

Because the oommunication system voltages are many times smaller than the 

60-Ez power, and because it is not necessary to operate with 60-82 excitation, 

the 60-82 operating voltage can be easily scaled while holding the impedances 

constant, with a significant transformer size reduction, The voltage scaling 

can be much larger than the ratio of the power frequencies voltage to 

communication voltage because the communication frequency is usually 100 times 

the power frequency. Thus, the operating flux of the transformer is much less 

at the communication frequency. "he scaling suggested here, then, is to hold 

the impedances constant and to scale the 60-& voltage appropriately. 

There are two kinds of transformers that need to be scaled for simulation of 

the distribution mtwork for PLC studies, especially for the distribution 

network at SDG&E These are the substation transformers and the injection/ 

di str ibut ion transformers, 

The substation transformers at SDGM Murray Substation are three-phase, 6+kV 

A-connected to 6.+kV Y-connected transformers with a capacity of 15 MVA (for 

open-air operation), 20 WA (for forcsd-air operation), and 25 to 28 MVA (for 

short term operation). The rating for the purpose of impedance calculations 

will be taken as the open-air rating. The injection transformers used at the 

same substation are of two types: 

(1) 

(2) 

Three each, singlephase 7200 V to 120/240 V, 25 kVA with Zs = 1.881L 

Three each, single-phase 12000 V to 120/240 V, 25 kVA with Z, = 

1.88B 

2-1 
zhey are used fa phaseto-ground and phaso-tcrphase excitatiozb respectively, 

for the commmication signals. 

For the threbphase (36) substation transformer, the rated load impedance for 

each pbrs is 

where 

5 = load impedance for each phase 

Vd = voltage for each phase 

S = substation transformer rating 

Assume scaling of tbs voltage so that 

VI = a Vd 

where 

a = the scaling factor (similar to a turns ratio) 

= the scaled phase voltage. Nor 

vS& 

S 

3 V*I* = -- 

where Id is tbs phase current and also 

where Zrd is fixed by assumption. 

Using Equation (2) in Equation (4) 

(3) 

is fixed by assumption, Isd is proportional to V by the relation 

Sd 

Because Z u 

vSd = -- 

Is& % 

where Ird is the scaled phase current. 

2-2 

(6) 
Therefore, 4uation (5) becaes 

Becauso the total rating is equal to the number d phases times tlm phase 

rating, Equation (7) can be interpreted as either 

(8) 2 

b (actual ating) = a (scaled rating) * 

or 

As an example calculation of Equation (91, assume that the 6.9-LV secondary 

voltage of the 15-WA substation transfomer is scaled dm to 69 V. Then 

Using 4uation (91, thca 

= 1.5 LVA 

Assume the transformer is scaled according to the above example. 

is: 

The question 

What are the remaining specifications? In determining the scaled current 

VS*ISb = -- VA 3 

or 

= -- 500 = 7.25 A IS6 69 

Ncm considering the transfoxmet impedance, 

zs4 = =L4 

(11.) 

(12) 

(13) 
where 

= the transformer equivalent series impede "' (not to be oonfused with a scaled value) 

IC = a fact= of proportionality (equal to 0.01 times the 

nameplate value of percent impedance) 

Some designers prefer to specify regulation instead of Zsdn SO another 

equation is meded. 

Now rmltiply &qaation (13) by Id, obtaining 

but 

so that 

or 

Id% = vd 

IdZd = k V1 (15) 

The value, k, is now recognized as the regulation of the transformer. As 

already rroted, k is usually obtained from the nameplate of the transformer. 

For distribution transformers, it is about 2%. Table 2-1 smmarizes the 

values for the transformers used at Murray Substation as well as the scaled 

values. 

small ea~~sformers mmlb' have a zs& that is primarily resistive, while 

larger transformers have a significant leakage inductance component as welt 

In larger transformers, the windings have a split design to hold the leakage 

inductance to reasonable values. Fa tlm small scaled transformers described 

above, the impedance is then resistive, which may require that inductances be 

added externally to simulata the actual transformer impedance. 'his is easily 

done, but the transformer must be sufficiently large to hold the resistive 

component down. The transformer probably should be designed for a 1% 

resistance component and have a 1% value d inductance added externally. 

Internal capacitance does not scale conveniently with size d the transformer. 

For smell transformers, the capacitance is smaller than that of the full-scale 

transformer. If needed, compensating capacitors can be added for simulation 

purposes. 
Table 2-1. Summary of Values and Sc8led Values 

for the SDG&B krry Substation Transformers 

Bating, S 

Number of Phases 

v* (wary) 

vi (secondary) 

Zrs 

zhms ratio 

Begolatiaa k 

(assmod for design) 

Scaling factor 

(Soaled rating)= 

'si (primary) 

Vd (secondary) 

'4 (primary) 

I4 (secondary) 

Substa tion 

15 MVA 

3 

69 kV 

6.9 kV 

1O:l 

9.52 (secondary) 

ohms 

1% 

0.095 abu 

(referred to 

secondary) 

100 

1.5 kVA 

690 V 

69 V 

0.725 A 

7.25 A 

Trand mer 

Y-A 

Injection 

25 kVA 

I 

12 kV 

1201240 v 

loo: 1 

5760 (primary) 

ohms 

1% 

57.6 ohs 

(ref erred to 

pri-ry) 

100 

2.5 VA 

120 v 

1.2 v 

0.021 A 

2.1 A 

Y-Y 

Injection 

- 

25 kVA 

1 

7.2 kV 

1201240 V 

60: 1 

2073 (primary) 

ohms 

1% 

20.7 ohms 

(referred to 

primary) 

100 

2.5 VA 

72 V 

1.2 v 

0.035 A 

2.1 A 

2-5 
The cor0 loss is proportional to the core volume and for the scaled 

transformer is many times less than for the full-scale transformer. But even 

at full scale, it is only a small percentage of the load, and it can be 

considered as part of the load. 

s18q 

If a transformer is scaled in both voltage and ourrent, and if the regulation 

is the same as the unscaled transformer, the series impedance of the scaled 

transformer is the same as that of the mrscaled transformer. Stated another 

ray, a three-phase 1.5-kVAD 69-V secondary P connectedl690-V primary, A 

connected, 1% regulation transformer rill have about the same series impedance 

Zd as 8 threephase lS-WA, 6.9-kV secondary, P oonnscted/6!l-kV primary, A 

connected, 1% regulation transformer. Inductance and capacitance are added 

externally to compensate for the fact that these parameters do not scale 

conveniently. 

2-6 
SECTION 111 

BdpMbpB DESCRIPTION 

Subst8tion Siruhtor 

The substation simulator contains three distributi n tr sformers ( oh 

simulating a 15-MVA unit), a total of six injection transformers for the 

purpose of injecting the PK! signal, a number of relays, and a power supply 

for the relays. A schematic of the substation simulator is shown in 

Figure 3-1. Table 3-1 also illustrates the values and scaled values of the 

SDGM Murray Substation transf ormer. 

A signal generator is used to inject the signal into the primary si& of the 

injection transformer. The substation simulator is designed to accommodate 

the six different signal injection possibilities (three phase-to-phase and 

three phaseto-ground choices). An additional transformer with a turns ratio 

of 1001 may be required between the signal generator and the primary si& of 

the injection transformer. The output of any injection transformer may be 

connected to the distribution line Simulator line-to-line, .line-to-neutral, or 

in any desired fashion. Figure 3-2 shows a phase-to-ground current injection 

method on Phase A 

Ihe substation simulator may also be used to check out other ideas. One such 

idea is the design of a directional coupler that is capable of rejecting noise 

coming into the substation from different feeders. Theoretically, this 

circuit can result in an approxinmtely lodB improvement in caamunications in 

a substation with 9 to 11 feeders, 

Feeder Simulator 

The feeder simulator has a panel containing 18 sections, Each section is 

labeled by a number, but the numbers are not necessarily in order. 

Figure 3-3 shows the configuration of the feeder simulator. Distribution lines 

are simulated in 100-m segments, hch segment requires two components that are 

called 'unit pairs'. With the exception of Section 23, which contains only 4- 

unit pairs, an individual section contains Sunit pairs. The first unit of 

each unit pair simulates the series resistance and inductance of the 

distribution line as a function of frequency. It also simulates the ground 

wire. Ihe second unit simulates the mutual inductance between lines (the 

threephase lines and the neutral lines). Ibe layout of each unit is shown in 

Figure 3-4. Various unit pairs represent different conductor sizes. The 

color circle in Figure 3-4 may be yellow, blue, or green, indicating the wire 

size of #WOO, #OD or #2 solid round copper wire, respectively. Table 3-2 

lists the characteristics of the feeder simulator sections. 

It should be noted that each unit pair is configured to simulate a 

distribution line in which: 

(1) All the threephase lines and the neutral line are located in a 

horizontal plane. 

3-1 
SOUTH SUBSTATION 

TRANSFORMER BANK 

*A 

TRANSMISSION : eB 

eN LINE 1 

12-kV 

D ELT A-WY E eC 

S 

"9 NL 

TRANSMISSION : BANK 2 

LINE 2 0 D ELTA-WY E 

0 

0 

0 

ec 

INJECT I ON TRAN SFORMERS 

A 4 N 

B 

II - I 

VAB I 

1 ' 'BC 

'CA 

CURRENT SENSING A 

I

6003 

eA 

eB 

eC 

ON 

1 

!A' - 0 TEST 4) P 

e 

e' 0 

e 

e 0 i' 

Figure 3-1. Schematic of the Substation Simulator 

3-2 

A 

AB 
Table 3-1. Values far the SDGU Murr8y Substation Transformers 

Substation 

3 

69 kV 

6.9 LV 

10: 1 

9.52 

0 . 095 

100 

1.5 LVA 

690 V 

69 V 

0.725 A 

7.25 A 

(second8ry) 

(second.rg) 

Trmsf ormers 

Y-A 

Parameter 4 eotion 

Number of Phases 

Vd(primry) 

V& ( second8ry 1 

zrd' ohms 

ztc' obas 

lbrns ratio 

SOdhg factor 

Scaled rating 

'4 (prirarp) 

'84 (Se-daV) 

Id (primary) 

Id (seoond.ry) 

vd = *SO Voltage 

5 = load impedance for each phue 

= transformer equivalent series impe&nce 

= scaled phase voltage 

Id = SC8hd phase current 

ZS4 

vSi 

1 

12 LV 

120/240 v 

loo: 1 

5760 

(primary) 

57.6 

(pr imry 1 

100 

2.5 VA 

120 v 

1.2 v 

0.021 A 

2.1 A 

P-Y 

Inj eo tion 

7.2 LV 

120/240 V 

60: 1 

2073 

(primary) 

20.7 

(primary) 

100 

2.5 VA 

72 V 

1.2 v 

0.035 A 

2.1 A 

3-3 
1 :a 

3-4 

i3=0 3 L - I 

Figure 3-2. Primary PhasetwGround Current Injection on Phase A 

(2) The ordering of the layout is Phase A. Phase B. Phase C, and 

neutral. 

(3) The distance between wires is 3.0 ft. 

(4) The height of the distribution pole is 30 to 35 ft. 

The scaling factor between the distribution line and the units is unity, in, 

the impedances are directly repeated. mere are 89 unit pairs. With all of 

the units connected in series, a 8900-a distribution system can be simulated. 

Othr Hardware 

In addition to the substation and feeder simulators, function generators. 

oscilloscopes, and other equipment may be required. 
SECTION 1 

1 

SECTION 2 

SECTION 3 

SECTION 4 

1 

SECTION 5 

SECTION 6 

1 

SECTION 21 

I 

SECTION 22 

SECTION 23 

SECTION 11 

I SECTION 12 

SECTION 13 

I 

I 

SECTION 14 

SECTION 15 

SECTION 16 

SECTION 31 

SECTION 32 

SECTION 33 

Figure 3-3. Schematic of Feeder Simulator Shoring Various Sections 

3-5 
PHASE A 

PHASE B 

PHASE C 

NEUTRAL 

COLOR CIRCLE 

GROUND WIRE 

Figure 3-4. Layout of Enoh Unit in a Unit Pair 

3-6 

00 

00 

00 

a 

00 
Table 3-2. Feeder Simulator Section Quaoterirtios 

Section 

1 

2 

3 

4 

5 

6 

11 

12 

13 

14 

15 

16 

21 

22 

23 

31 

32 

33 

Number of Pairs 

Contained 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

5 

4 

5 

5 

5 

code color 

Yellow 

Green 

Green 

Yellor 

Blue 

Green 

Yellor 

Yellor 

Yellow 

Yellor 

Blue 

Blue 

Blue 

Green 

Green 

Blue 

Blue 

Green 

Wire Size 

Simulated 

3-7 
SECTION IV 

I. 

SAN DIBQO GAS AND ELECTRIC STUDY 

- 

v1 

v2 

"3 

Introduction and Purpose 

The SDG@ Murray and El Cajon Substations and distribution systems were 

selected as the sites for a demonstration, in part, to study performance of a 

RC system on a distribution system of a type that no previous measurements 

(experience) had been obtained. 

- 

'13 

'23 

y33 - 

The Murray and El Cajon Substations and distribution systems were different 

from previous sites of PLC system installations where test data were 

available. At these sites there were significant numbers of both phase-tcr 

phase (for overhead lines) and phase-to-ground (for underground lines) 

connected loads. A Rc signal injection system was devised to accommodate the 

six different signal injection possibilities (three phase-to-phase and three 

phase-to-ground choices). 

- 

yll 

y21 

'3 1 1 

In August and October, 1979, verification and trouble-shooting tests were 

performed by American Science and bgineering (AS&E) at SDG&E These tests 

left a number of unanswered qwstions, which JPL became active in answering. 

Part of that activity was to explain an unexpectedly large cross-coupling of 

voltages on the various substation bus phases for the injection choices. The 

simulator constructed by JPL was used to provide insight into this problem. 

Tests with this simulator pointed to the type of load (Y or A) as a large 

contributor to this cross-coupling, 

This section reports on the analyses of the injection system installed at 

SDG&E and compares it to laboratory and field tests. Close correspondence 

between analysis and tests was obtained. The results show that strong crosscoupling between several bus voltages should be expected. 

Analysis 

Preliminary tests on a laboratory simulator of tho Murray Substation indicated 

that the voltages on the substation bus because of currents injected into 

signal injection transformers are sensitive to the makeup of the load 

admittances. The assumption is, therefore, that the admittances are made up of 

Y and A admittances as shown in Figure 4-1. 

In general the relationship between currents and voltages in a throbphase 

system can be represented by an admittance matrix as follows: 

y12 

y22 

'32 (17) 

The immediate problem is to solve for the Yij, i = 1, 3, and j = 1, 3, in 

Bquation (17) in terms of the admittances shown in of Figure 4-1. This is 

4-1 
done by setting the two voltages equal to zero and 

13. sooh as: 

that yields 

1 

P 

e 

'11 

'21 

'3 1 

'11 

'21 

'3 1 

'12 

'22 

'32 

= 

- 

'13 

'23 

'3 1 - 

'10 + 

solving for il 12 .nd 

"1 

0 1: 0 

52 + '13 

"12 

-'13 

(18) 

- 

'23 

3 2 I - 

Figure 4-1. Substation BUS Load Admittances 

4-2 
~~ 

Successive permutations of the indices for setting the voltages equal to zero 

resul t in : 

- 

il 

i2 

i3 - 

P 

'10 + '12 + '13 -'12 -'13 

23 -I! -'12 '20 + '12 + '23 

-'13 -Y 23 '30 "13 "23 

v1 

v2 

v3 

(20) 

It is reasonable to assme that the substation bus load is klanced, making 

'10 = '20 '30 * 'I! 

and 

Y12 = '23 = x31 = PA 

Matrix (20) now becomes 

P' + 25 

-'A 

"A 

-'A 

Y' + 25 

-'A 

-yA 

-'A P' + 25 

Further assme that the total conrrscted substation load is 

total substation load = S 

Let 

P load 

total load uhere 0 k 1 

theraf ore. 

Y load = S k 

A load = S (1 - k) 

or 

total substation load S = S k + S (1 - k) 

v1 

"2 

v3 

(21) 

(22) 

(23) 

(24 1 

(25) 

(26) 

(27) 

(28) 

4-3 
Using the assumption that the loads are balanced, the load admittance 

magnitudes can be calculated as follows: 

c -* 7 

v1 

v2 

v3 

S (1 - k) i -- Sk+2S(l-k) - S (1 - k) -- 

39 

3v2 V2 3v2 39 

3v2 3v2 V2 3v2 

1 

V2 3v2 3v2 

-S (1 - kl __ Sk+2S (1-k) -- 

-S (1 - k) - 

S (1 - k) i2 = 

S (1 - k) - S k + 2s (1 - k) 3 i 

- -1 -1 

and 

- 

v1 

v2 

v3 

IS 

(1 - k) = s (1 - k) 

'A= 33 

(3 0) 

where V is the 6042, linet-to-lins voltage. 

Substituting Equations (29) and (30) in (23) yields the following matrix: 

Collecting terms, Mntrix (31) becomes: 

S 

=2 

r 

k+2 

k-1 

k-1 

B 

k-1 k-1 

k+2 k-1 

k-1 k+2 

(32) 

Matrix (32) is not in the right form because it is the solutian of [I] whsa it 

is the [VI that is needed. Matrix (32) must be inverted or 

3$ =- S 

- 

k+2 k-1 k-1 

k-1 k+2 k-1 

k-1 k-1 k+2 

B 

-1 

1 i 

i2 

3 i 

(33) 

4-4 
Simplify Equation (33) by ding the following substitutions: 

- 

v1 a B B 

3vz B a B 

B B a 

Pv2 S 

v3 

A - * J 

and 

il 

2 i 

i3 

* L 

&quation (33) beooees 

a=k+2 

BSk-1 

(34) 

(35) 

(36) 

Using Craawr's Rule for the matrix inversion yields: 

Factoring: 

and 

Equation (37) 

4-5 
Using Equations (34) and (35) for the terns involving a and p, 

(a-j3)= k+2-k+1 -3 

(a+B)= k+2+k-1 =W+1 

(a- 2s) = k + 2 + 2k- 2 =i 3k 

In setting up the problem, a choice is available to write the original 

Equation (17) as either 

or 

Ihe latter is the form of Equation (39). 

me zij for i i= I, 3, and j = I, 3, values are more difficult to obtain than 

for i = 1, 3, and j = 1, 3, but the Pij requires the matrix 

E:er%$a Both methods lead to the same result with about the same amount of 

algebraic manipulatioa 

Now, assume a current of I amperes is injected in the low side of the 

injection transformers (with a current source) as shorn in Figuxes 4-2 and 

4-3. The tarns ratios for the injection methods indicated in Figures 4-2 and 

4-3 are 

12,000 

120 v 

-6 100 =- 

6 a= 

corresponding to tbe phase-to-ground injection method and 

corresponding to the phasbt<rphase injection method. 

(40) 
1 '1 

'23 

i3 = 0 3 L - 

Figme 4-2. Primary Phaserto-Grormd CPtrent Injection Method on Phase 1 

1 '1 

"12 /5 

I L - 

0 yJ 

c 

.. 

l2 = I, 

2 L - 

1 :a' 

ig =O 3 L - 

Figure 4-3. Primary Phaserto-Phase Current Injection llethod on Phases 1 and 2 

4 -7 
a!9 i2 = 0, and i3 = 0 (42) ilp 100 * 

- - -- - 

1+W l-k l-k 16 

v1 100 

'2 s3 l-k 1+2k l-k 0 S 3k 

v3 l-k l-k 1-2k 0 

i - 1 -3 

for the phase-to-ground injection method on Phase 1 and 

(44) 

il = 100 I , i2 = -il = -I - 8ndi3=o (43 1 loo , 

1 + 21; 

l-k 

l-k 

d 

for the phase-to-phase injection method on Phases 1 and 2. 

becomes 

Equation (39) 

v1 

v2 I1 v3 

= 

or 

for the phase-tcrground injection systm on Phase 1, and 

[1+2k l-k 1-k 

or 

PI 

s 100 

1- l-k 

-1 

0 

I 

100 

I 

100 

0 

- 

-- 

for the phase-to-phase injection system on Phases 1 and 2. 

(45) 

(46) 

4-8 
@prtions (45) and (47) give the *ase-tcrgroand voltages for the injection 

methods stated. Two other sets of voltages are of interest: the phase-tophase voltages for the two injection methods (phase-to-ground and phase-tophase). To calculate these (see Figure 4-11, note that 

- - 

1 

2 

3 

i 

i 

i 

J A 

V12 = v1 - v2 (48) 

Va = v2 - v3 (49) 

(50) '31 "3 - "1 

- - 

v12 

= '23 

'3 1 L - 

lheref ore, 

- 

'1 

iz 

3 i 

- 

- - 

v12 

'23 = - 9 

'3 1 

S 

1 

- v2 

S 

r - 

v12 

V23 

'3 1 

1 A 

1 

3k 

- 

= - d 

S 

(51) 

or 

1 -1 0 

0 1 -1 

-1 0 1 (52) 

Using 4uations (42) in Equation (52) to calculate the phaseto-phase voltages 

for phase-tcrground injection current into Phase 1 yields the following: 

d =- s 

1 -1 

0 1 

-1 0 

-[:I 100 

0 

-1 

1 

(53) 

(54) 

4-9 
Similarly, using 4uation (43) in 4uation (52) to calculate the phase-tophase voltages for phase-t-phase injection current into Ruses 1 md 2 yields 

the following: 

1 

0 

-1 

-1 

1 

0 

[ 4 

A summary of Equations (451, (471, (541, 

0 

-1 

1 

and (56) 

I 

100 

I 

100 

- 

-- 

0 (55) 

is shown in Table 4-1. 

Equations (45) and (56) show strong cross coupling terms. 4uation (45) shows 

that the phase-to-ground voltage can go to infinity for k = 0. This is 

because the iqjection current has no finite impedance return path. All the 

voltages can be put into perspective if the appropriate voltage divider action 

of the network is inspected closely. 

Laboratory Verifioation Tests 

Tests were performed on the substation simulator for all modes of excitation, 

five k factors, and all modes of signal extraction. Zhe assumptions for the 

tests were: 

I = 1.0 A (Injection current on secondary) 

S = 30 MVA (Equal to capacity of two 15-WA transformers in parallel) 

v = 12,000 v 

Results of the calculations and measurements are shown in Table 4-2. 

Correspondence be tween calculations and measurements are generally very good 

except where k = 0. In the setup, k could not actually be equal to zero 

because half the injection transformers were connected in Y and were present 

during the test. 

4-10 

~- 
Table 4-1. Smry of hlysis 

- 

v1 

v2 

v3 L 

BUS 

Voltage 

1% 

100 

Phase-twGround 

Current Inj eciioa 

on Phase 1 

- 

1 

-1 

h 

Phase- twPhase 

Current Ij ec t io n 

on Phases 1 and 2' 

- 

2 

-1 

-1 

Phase-t<r 

ground 

voltage 

.. 

v12 

"23 

'3 1 

equation (45) 

11 + P 

1' -k 

v1 

v2 

v3 

Equation (47) 

$1 

"V 100 

1 

-1 

0 

Phase-tcr 

mvoltage 

Eqaation (54) 

V2 =- S 

'3 1 

Equation (56) 

=- 9 

S 

a 

To get the resulting voltages for other injection phases, permute 

the appropriate indices. 

4-11 
Table 4-2. Sommary of Calculations and Laboratory Verification 

Phase- to-Ground 

Current Injection 

Vol tages on Phase 1 

Ph ase- t 0- Phase 

Current Injection 

on Phases 1 and 2 

.=l 

Same as all 

Y load) 

; = 0.8 

E = 0.6 

K = 0.2 

t = 0.0 

(Same as all 

A load) 

Pha so- to-Ground Vo 1 tag e s 

Calculated 

v12] [o*q 

"3 

0.0069 

v1 

v2 

v3 

v1 

v2 

"3 

0.1016 

0.0185 

0.0185 

0.1939 

0.1108 

0,1108 

Me as ur e d a 

0.0008 

0.0069 

0.1000 

1.84 

Calcula ted 

0.0480 

-0.0480 

0.0 

a Mens or ed 

0.0480 [ ::2 ] 

Phase-to-Phase Voltages 

Signs were not noted in the tests. a 

4-12 
Field Yeasurements 

Measurements on the SDG&E Murray Substation North Bus through capacitor 

couplers are shown in Table 4-3. There is a correspondence between these 

measurements and the equations summarized in Table 4-2. 

Table 4-3. Hurray Substation North PLC Bus Voltage Measurements Made by &&E 

(Reformatted to Correspond to Tables 4-1 and 4-2) 

Phase-to-Ground 

Current Injection, 

10 A 

kG &G EG 

Phaseto-gromd, a 

kG 3.68 1.28 1.29 

B-G 1.6 4 1.89 

(FG 1.6 1.76 4.21 

Phase- to-Phase 

10 A 

Current Injection, 

bB &C *A 

1.41 0.77 1.41 

1.68 0.98 0.22 

0.48 1.68 1.17 

a Phase-to-phase, 

kB 

B-C 

C-A 

No 

measurements 

avail able 1.76 1.60 2.4 

2 .% 0.85 1.12 

1.18 2.48 1.31 

Ihe derivation of the equations in this report assumes that the impedances 

were balanced, Borevet, the actual bus impedances may not be balanced. As a 

result, some variation between the measurements and calculations can be 

antioipated. Also, because the load on the substation or the ratio of the Y 

load to the total load (k) is unknown, the expected voltages cannot be 

predicted with precisioa Nevertheless, om can work backward from the data 

to calculate these voltages to determine if they are reasonable and 

consi stent . The diagonal terms of the first 9 numbers of Table 4-3 (3.68, 4, and 4.21) 

add correspond to (1 + W) of Equation (45) (see Tsble 4-11, and the offdiagonal terms should correspold to (1 - k) of Equation (45). If the diagonal 

and the off-diagonal terms are weraged (to remove the effects of unbalanced 

loads) and the ratio taken, then: 

(1 + 2k) <diagonal teras> - 3.96 

(1 - k) <of f-diagonal terns> 1.57 

where < > means 'average' 

Solving for IC: 

k = 0.33 

4-13 
Ihe value k = 033 is a reasoxmble value far the amount of underground (Yconnected load) to overhead &connected load) lines on the Nurray Substation. 

zhis measured Val- of k is at the signalling frequency and may not fully 

reflect the value of k at 60 aZ, Using the value k = 033, one can calculate 

the substation load through either the (1 - k) or the (1 + 2k) term of 

Equation (45). If the value of (1 - k) is used, then 

v" 113 - 1-k 

s 300 k (offdiagonal toms> = 1.57 = - 

then 

\;L 16-1-k s.. - 

1.57 

- 

300 

- 

k 

whereas 

then 

I = 10A 

S = 10.75 WA 

This value is about 8 third of the OA (oil-immersed, self-cooled), 60-82 

rating of the parallel transformer banks [Equations (48) and (4911 installed 

in the -&E Yurray Substation North Bus and seems to be a reasonable value 

for operation at the signalling frequency. 

Ihe 9 numbers in the upper right quadrant of Table 4-38 corresponding to 

Equation (47) from the analysis, show a sizable departure from what is 

expected. There should be at least three entries that are closer to zero than 

the data show. O'Iese are those corresponding to V, for phases A-B 0mr-t 

injection, VAG for phases IfC, and VBG for phases C-k) This speaific 

measrrtement is sensitive to the unbalances of the load Eowever, if the rest 

of the data corresponding to Equation (47) are averaged, the bus load can be 

calculated to determine if it is consistent with the calculation of the 

preceding paragraph, then 

A 

<1.41, 1.41, 1.68, 0.98, 1.68, 1.17) = 1.39 = $ & 

or .I 

that is consistent with the previous valm calculated. 

'00 data of the lower right quadrant of Table 4-3, corresponding Equation 

(56), indicate that the diagonal terms should be twice the off-diagonal terms. 

If these terms are averaged to remove the effects of the load unbalance, then: 

= 2.005 <diagonal terms> 2.6133 

<of f-diagonal terns> 1.31033 

4-14 
Except for the unbalance there is a good correspondence between the analysis 

and the field measurements. The data can also be used to calculate the 

substation load at the injected signalling frequency by using Equation (56). 

Then : 

$1 <off-diagonal terns> = 1.31 = - - 

s 100 

or 

$1 s=- - = 10.99 LNA 1.31 100 

that is consistent with the two previous calculations. 

A summary of the substation load (at signalling frequency) calculated from the 

test data is: 

from Equation (45) Load = 10.75 MVA 

from Equation (47) Load = 10.36 MVA 

from Equation (56) Lord = 10.99 MVA 

Conolosiors 

Very good correspondence was obtained between analysis. simulation results. 

and field test data. Therefore. a high degree of cross coupling between the 

bus voltages corresponding to the signal injection system should be expected 

at the SE&E Murray Substation. 

4-15 
SECTION V 

SOYYARX AND CON(zoSI0NS 

To improve the reliability of service and economy of operation, many utilities 

and some government agencies are considering the possibility of distribution 

automation Load management, of the kind that has been practiced for a number 

of yeus in the United States and abroad, can be considered to be one specific 

subset of distribution automatioa Other aspects of distribution autaaation 

would include voltage control in the distribution system, feeder reconfiguring 

following faults, load redistribution, .and automatic meter reading. 

Ihe different aspects of distribution automation each impose an additional 

burden on the communication system. In spite of the low data rate usually 

experienced with PLC systems, they are nevertheless receiving attention again 

as possible communications media in the implementation of distribution 

automation. Newer and more ingenious uses of RC are still being developed. 

Ihe simulator described in this report may be useful for analyzing signal 

propagation in distribution systems in rays as yet untried. The simulator is 

a detailed model of a distribution system, including the phase-twphase and 

phase-to-ground effects and the skin effect of the conductors. Because of 

this it should be possible to use it to study single-phase and multi-phase 

injection over a variety of frequencies, and over a number of possible line 

and cable designs. 

I 

l 

Ihe usefulness of the simulator may continue =til a different and distinctly 

better communications channel is implemented in the distribution system. For 

many utilities, such a development amy be a long way in the future. 

I