Performance Criteria for Power-System Compatibility 

Fran~ois D. Martzloff 

National Institute of Standards and Technology * 

Gaithersburg, MD 20899 

Abstmct - Power electronics create an opportunity for 

better utilization of electric energy but can become a 

source of problen~s if the electromagnetic characteristics 

(immunity and emissions limits) of the equipment are not 

compatible with the characteristics (avoidable and unavoidable disturbances) of the power supply. Well-defined 

equipment performance criteria an help end-users obtain 

better compatibility, reliability, and cost effectiveness of 

the equipment - power supply combination. 

I. INTRODUCTION 

The ever-expanding application of power-electronics 

loads, the increasing dependency upon information 

processing systems, and the explosive development of 

power-system disturbance monitors (cum graphics) have 

produced a new level of concern about the compatibility 

of load equipment and power supply. Power-electronics 

loads are accused of polluting power delivery because 

of their nonlinear charact&istics and the utilities are 

accused of delivering poor power quality. Meanwhile, 

the rapidly growing number of users of power-system 

disturbance monitors proudly display pictures of their 

'glitch of the month' (in the way senior engineers used 

to pull pictures of their grandchildren out of their 

wallets) all to lament how bad the situation has become. 

It is time to take a fresh look at the situation and stop 

pointing fingers; instead, available resources should be 

applied to obtain hetter compatibility between hardware 

and software. Better compatibility is also needed 

among the three partners irrevocably involved, for 

better or for worse, in the power-electronics arena: the 

equipment suppliers, the electric power suppliers, and 

the end-users. 

A new term has emerged and gained popularity in 

recent years: Pobrw Quality. The basic need for 

satisfactory operation of equipment is well perceived by 

all. However, depending upon the point of view of 

those using this term, the interpretation of the term and 

the approach in achieving its objective are different. A 

clear definition, accepted by all interested parties, has 

yet to be developed. 

* Electriciry Divkion, National Institrcre of Standards and Technology, U.S. Deparnnenr of Corn~nerce, Technology Ad~ninisrrarion. 

It may be useful to look back and benefit from the 

experience gained, long ago, in honing the concepts of 

electromagnetic compatibility because the quest for 

power quality proceeds along the same path as the 

broader topic of electromagnetic compatibility. 

The performance of electrical equipment can often be 

described in fairly simple terms. Therefore, the subject 

of ratings, dimensions, and tolerances is readily addressed by the product standards developed by the 

manufacturers or by the purchasers, working jointly or 

separately. However, performance of equipment can be 

adversely impacted by electromagnetic disturbances and, 

conversely, the operation of equipment can emit disturbances that impact other equipment. Thus, avoiding 

electromagnetic interfeteen (EMI) became an important 

field of engineering, but all too often it became a process of correcting problems rather than anticipating and 

preventing them. A more successful approach, both 

from the point of view of sound engineering practice 

and from the connotations of semantics, was the development of the concept of Electromagnetic Comparibiliry 

(EMC). One way to look at power quality issues would 

be to consider them as an interesting, dedicated subset 

of EMC, limited to the area of low-frequency conducted 

phenomena, as opposed to the 'dc-to-daylight' domain 

of the IEEEIEMC Society. An invitation for presenting 

a paper at this forum is an opportunity to complement 

the usual power quality dialogue, limited to end-users 

and electric utilities, by a three-way discussion that will 

include original equipment manufacturers (OEMs). 

11. THE NEED FOR STANDARDS 

Mass production of electrical and electronic equipment 

for the world market requires standards of world-wide 

applicability. Such standards are reference documents 

that provide solutions to technical or commercial 

problems in the transactions between contracting parties 

concerning products, goods or services. Standards act 

as a foundation to any contract. 
The development and implementation of power-quality 

standards is presently incompletely coordinated, in spite 

of all the efforts to provide coordination and liaison 

between the various standards-writing bodies. As an 

example, the European Directives on EMC take the 

position that electricity is a product, therefore subject to 

product standards of quality [f]. However, the conditions for optimum compatibility between the needs of 

equipment and the inherent characteristics of a power 

supply are not yet defined. 

Product standards have reached a state of development 

where equipment survival in the field is adequately 

addressed, but the more subtle immunity to unavoidable 

disturbances is not addressed, to wit blinking clocks or 

industrial processes that shut down because their control 

systems lack sufficient ride-through capability during 

momentary power interruptions. Conversely, efforts to 

limit emissions of disturbances into the power system 

caused by normal operation of the equipment have faced 

a difficult challenge of achieving consensus, nationally 

as well as internationally [2], [3]. 

Power Quality Surveys and Electromagnetic 

Environment Charalteriz~tion 

From a handful of surveys of transient disturbances in 

the sixties and seventies, we now witness a multitude of 

large scale monitoring programs aimed at detining the 

power quality of the energy being delivered to endusers. An unresolved issue at this point is the translation (transformation) of objective measurements of 

electrical disturbances into a subjective statement of 

'good power quality' or 'poor power quality' - the 

statement that typical decision-makers desire, but that 

engineers have difficulty in defining. 

The term PONTT Quality has now gained too wide an 

acceptance to be changed, but it fails to convey the 

concept of reciprocity between the parties. A debate at 

a recent meeting of the IEEE Standards Coordinating 

Committee on Power Quality pointed out that a more 

accurate description of the Committee's scope would be 

Power Comparibility - but the committee resolved, with 

regrets, to go along with the entrenched usage. The 

IEEE attempts addressing these concerns with the steady 

development of voluntary Guides, Recommended 

Practices, and Standards. However, the process of 

consensus standards is all too often very slow, and 

sometimes delivers only broad (generic) rather tha

specific documents because of the lowest commo

denominator effect inherent in the consensus process. 

Several national or international documents have bee

developed to classify the characteristics and disturbance

of power systems. For instance, the normal steady-stat

conditions in U.S. power systems are defined in ANS

C84.1-1989 [4]; surges are described in ANSIIIEE

C62.41-1991 [5]; and an IEEE Guide is under devel

opment to describe the range of disturbances [6]. O

the international scene, the variations in steady-stat

conditions and the types of transient disturbances ar

addressed by the Technical Committee 77 (TC77) o

Electromagnetic Compatibility of the Internationa

Electrotechnical Commission. Table 1, excerpted from 

documents under consideration by the TC77 shows th

list of these phenomena that cause radiated as well a

conducted disturbances 171. 

TABLE I 

PRINCIPAL PHENOMENA CAUSlNG 

ELECTROMAGNETIC DISTURBANCES 

Conducted low-frequency phenomena 

- Harmonics, intchnnonics 

- Signalling voltages 

- Voltage fluctuations 

- Voltage dips and intemptions 

- Voltage unbala~~cc 

- Powcr-fmquency variations 

- Induced low-frequency voltages 

- DC in AC nctworka 

Radiated low-frequency phenomena 

- Magnetic fields 

- Electric fields 

Conducted high-frequency phenomena 

- Induced CW voltages or currents 

- Unidirectional transients 

- Oscillatory transients 

Radiated high-frequency phenomena 

- Magnetic fields 

- Electric fields 

- Electromagnetic fields 

. Continuous waves 

. Transients 

Electrostatic discharge 

Nuclear electromagnetic pulse 

Source: IEC 77(Secretariat)lO8 m 
A useful development in designing for electromagnetic 

compatibility is the recognition that equipment can be 

described in terms of several generic ports (Figure 1) 

representing the path of entry or emission of electromagnetic disturbances [8]. By breaking down the 

complex coupling of the equipment to its environment, 

addressing compatibility issues becomes more manageable. However, one should not make the error of 

presuming that these ports have no interaction, inside or 

is the lack of understanding and cooperation among the 

three partners. Until such time as the usual process of 

voluntary standards (typically in North America) or the 

government-issued Directives (typically in Europe) 

impose full disclosure of the immunity and emission 

characteristics of the equipment, it will not be possible 

to design a system for predictable and reliable powersystem compatibility. 

outside the equipmeit. 

System Compatibility Pegormance Criteria 

Enclosure port 

-v ,\v/, L' 

, L Control 

I ( APPARATUS 11 

Earth 

Port 

Source: Adopted from CENELEC prEN 50 082-2 (81 

Figure 1 

Six ports of electronic equipment for entry 

or emission of electromagnetic disturbances 

Load Equipment Characterisrics 

An essential element of electromagnetic compatibility 

is the characterization of load equipment - both its 

immunity levels and its emission levels. The basic 

concept of compatibility, expressed in the IEC definition, is that equipment should have a high probability 

"to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances to 

anything in that environment. " 171. 

While simple and easy to agree with in principle, this 

concept is difficult to apply when the immunity and 

emission characteristics of the load equipment are not 

available to the system designer. This unavailability is 

results from either insufficient recognition of the issue 

or reluctance by some OEMs to publish data that might 

be misconstrued as a competitive weakness of their 

product. Actually, the weakness in the overall situation 

To remedy at least in part this undefined situation, 

System Compatibility (SC) performance criteria have 

been developed by the Power Electronics Applications 

Center (PEAC). This development is in response to the 

growing need for ensuring equipment compatibility at 

the interface between the utility and the end-user loads 

[9]. Load equipment OEMs generally do not have a 

sufiicient knowledge base or the incentives to allocate 

their limited resources to research all aspects of utility 

compatibility for equipment that may be installed by 

third parties. Individual users may not have the appreciation of potential problems and the leverage necessary 

to bring about changes in equipment design. Last but 

not least, Architectural and Engineering firms (A&E), 

while understanding the potential incompatibilities, may 

lack incentives or leverage to obtain redesign of load 

equipment or reconfiguration of the power supply. 

Therefore, the main purpose of these SC criteria is to 

facilitate reconciliation of the inherent limitations of the 

power system environment with the characteristics of 

ever-changing electronic loads. The SC documents will 

provide a uniform approach to system compatibility 

until such time when the usual, slower standards 

development will have caught up with the fast-changing 

technology. 

The System Compatibility approach is based on a 

three-step process: 

1. Determine the electrical characteristics of the 

environment. 

2. Determine the immunity and emission characteristics of candidate load equipment. 

3. Identify the need, if any, of some interface 

between the environment and the equipment. 
For the purposes of the SC process, the characteristics 

of the environment can be obtained from environment 

description documents such as [5], (61 or [7]. In the 

absence of sufficient docun~entation, the immunity, 

emission, or mitigation characteristics need to be 

determined by tests. To be consistent and fair, the tests 

must be conducted according to a well-defined protocol, 

hence this development of SC performance criteria. 

The tests can then demonstrate that specific equipment 

is capable of operating in that environment, will not by 

itself degrade the environment, and involves a minimum 

of undesirable side effects. 

These SC performance criteria tests are by necessity 

limited to the major aspects of compatibility and do not 

purport to replace more comprehensive tests performed 

by other parties, for instance those required for design 

engineering, regulatory compliance, or customer 

acceptance. The SC criteria have been developed from 

the point of view of electric utilities in consultation with 

other interested parties, including OEMs and end-users. 

111. THE SC DOCUMENT FAMILY 

The SC performance criteria provide a timely step in 

the application of power electronics equipment through 

objective testing for equipment of interest to electric 

utilities. For instance, some utilities are offering a 

comprehensive surge protection system to their custonlers, or are promoting energy savings through the use of 

electronic ballasts. To ensure success of such offerings, 

the utilities need to assess the performance of candidate 

devices offered by several OEMs. The test results are 

presented within a context of broad compatibility, not as 

a pass-fail judgment; expectations and results are 

presented to the sponsoring utility for analysis and final 

decision. 

By making these criteria available to industry, it is 

expected that more consistent methods for evaluating 

power-system compatibility will be achieved. Reaching 

this goal will be facilitated by the gathering of application experience in the fast-evolving field of power 

electronics. This experience will then provide the basis 

for the usual standards development. The ultimate 

result will be more reliable and more cost-effective 

application of power-electronics equipment in an 

environment which is continuously evolving. 

At the present time, several SC documents have been 

completed or are near completion; it is envisioned tha

the concept could be expanded to many more types o

equipment. Table I1 shows the list of the major catego

ries of documents under consideration, each to be 

subdivided into specific devices. For instance, the 

Power Conditioning Equipment category would include 

photovoltaic equipment, surge-protective devices

uninterruptible power supplies, etc. Among those, the 

rationale for documents in progress is briefly described 

in the following paragraphs. 

TABLE I1 

SYSTEM COMPATIBILITY DOCUMENTS 

UNDER CONSIDERATION 

A. POWER CONDITIONING EQUIPMENT (SC 001-199) 

FEED BACK (CO-GENERATION) 

FEED FORWARD (CUSTOM POWER) 

B. RESIDENTIAL LOADS (SC 200-399) 

13-0-V LOADS 

240-V LOADS 

C. COMMERCIAL LOADS (SC 400-599) 

s',N,G,Lz;P,H,A,S,EL,O,A,DJ 

D. INDUSTRIAL LOADS (SC 600-799) 

LESS THAN 7.5 kW (10 hp) 

GREATER THAN 7.5 kW (10 hp) 

E. UTILITY EQUIPMENT (SC 800-999) 

METERING AND CONTROL 

POWER 

F. POWER LINE MONITORING EQUIPMENT 

(SC 1000-1099) 

SC-1 I0 - Surge-Protective Devices Used in 

Low-Voltage AC Power Systems 

Surge-protective devices are applied in increasing 

numbers by end-users and now by some utilities on the 

meter side of their secondary systems. The surge 

current-handling capability of these devices ranges from 

0.5 kA to 10 kA, with a large number of suppliers 

offering these devices for installation at the service 

entrance or at receptacles within a building. Many 

OEMs also include these devices in the power port of 

their products. Some utilities now offer to their customers installing surge-protective devices with a guaran- 
teed protection. In such schemes, a high-energy 

arrester is installed at the service entrance, combined 

with protective devices connected next to the sensitive 

appliance [lo]. 

The voluntary standards development process has not 

kept pace with the rapid development and application of 

these devices, in particular the coordination of two 

devices installed within a short distance of each other by 

uninformed end-users [I I]. (Utilities offering the 

combined protection are in a better position to obtain 

coordination among the devices which they install, but 

still have no control over devices installed within the 

premises hy the occupant [12] .) 

Another aspect that has not been comprehensively 

addressed is the failure mode of these devices; many 

test standards generally aim at demonstrating a specific 

rating, with only a passlfail criterion, and the procedure 

does not go into failure mode determination. In contrast, SC-I I0 includes a test procedure to determine 

failure modes. 

SC-120 - Reference Equalizers Surge-Protective 

Devices for Power arld Commurlicatiorls Systems 

The increasing use of equipment that includes a power 

port and a communications port, as defined in Figure 1, 

(cable TV receivers, smart telephones, Fax machines, 

desk-top publishing systems, distributed computer 

systems, industrial process control systems, etc.) has 

created a new problem in surge protection. Appropriate 

surge-protective devices correctly but independently 

applied to the two ports might not provide adequate 

protection against the problem of differences in the 

voltages appearing at the two ports during operation of 

one protective device. 

To remedy this situation, OEMs are offering a device 

that routes both the power and the data connections 

through a single enclosure where the protective devices 

for each port share the same ground reference. Initially 

dubbed 'local ground window' [13], a new generic 

name of 'Surge Reference Equalizer' is now proposed. 

The SC-120 document describes a test schedule that 

exercises the protective devices of both the power port 

and the communications port (telephone or cable TV), 

separately and in combination. 

Another compatibility concern is raised by the increase in harmonic currents produced by the new 

generation of power electronics. Possible areas of 

concern include the overheating of transformers and 

neutral conductors, interference associated with spurious 

zero-crossings, errors in revenue meter accuracy, and 

improper power-system control. The following are 

examples of SC documents addressing these concerns 

through performance test criteria. 

SC-410 - High-Frequency Fluorescent Ballasts Used in 

Indoor Lighting Systems 

The increasing emphasis on energy conservation and 

the development of electronic ballasts have led some 

electric utilities to offer incentives to their customers for 

using these ballasts. However, in the present state of 

the market and standards development, these ballasts 

can create compatibility problems for users as well as 

for utilities. Interest in this issue is keen among both 

parties, hence the development of the performance 

criteria document for this type of equipment. 

SC-610 - Adjustable Speed Drives Used in Commercial 

and Industrial Facilities 

The accelerating trend in applying adjustable speed 

drive systems provides a classic example of the race 

between an emerging technology and the development 

of adequate compatibility. These devices produce 

current harmonics (the emission aspect of EMC) and 

many are very susceptible to power line disturbances 

(the immunity aspect of EMC). At this stage of the 

development and application of these drives, it appears 

that more effort is needed in addressing their electromagnetic (power system) compatibility. 

SC-920 - Dry-Type Service Transformers Used in 

Commercial and Indusrrial Facilities (k Factor Rating) 

Here again, concerns about harmonic current effects 

have led to new approaches in rating transformers 

exposed to these currents, by applying a derating factor 

('k Factor') reflecting the harmonic loading. These 

concepts have not been fully explored and consensus on 

their general applicability has not yet been reached. 
Therefore, the 'living document' nature of the SC 

criteria lends itself well to addressing the compatibility 

and performance aspects of this type of new, changing ['I 

equipment. In such rapidly moving technologies, the 

development of a corresponding SC document can 

address the need for interim data. Availability of these 121 

documents will then give breathing and reflection time 

for the development of appropriate standards and a full 131 

consideration of the EMC issues. 

CONCLUSIONS PI 

The development of System Compatibility Perfor- L61 

mance Criteria was undertaken as a contribution 

toward better operational compatibility at the inter- ~71 

face between end-users and electric utilities. PI 

REFERENCES 

Martzloff, F.D.. and Mendes, A., "Standards: Transnational 

aspects," Proceedings, First Intenwional Conference on Powe

Qualify: End-Use Applications and Perspectives, Gif-sur-Yvette

France. 15-18 October 1991, pp. 31-34. 

lEEE Draft P5 19, 199 1 - Recommended Practice for Harmonic 

Control. 

IEC Std 555-2 -Disturbances caused by equipm~nt connected t

the public low-voltage supply system, 1990. 

ANSI C84.1-1989 - American National Srandord for Electric 

Power Systems and Equipmen! Voltage Ratings. 

ANSIIIEEE C62.41- 1991 - Reconuncnded Practice on Surge 

Voltages in Low-Volrage AC Power System. 

lEEE Draft P1250 - Guide on Service to Equiprnenr Sensitive l

Momentary Volfoge Disturbances. 

Draft International Standard 77(Secretariat) 108: Clnssifimtion o

Electromagnetic Environmenrs, August 199 1. 

CENELEC prEN 50 082-2. DraR 1991 - Generic Immunity 

Standard. 

These documents neither have nor seek the status 191 

of standards, but they offer a shared medium to the 

three-partner community of end-users, utilities, and 

original equipment manufacturers. This sharing of 

[lo] Maher, A.M., "Residential transient voltage surge suppnzssion needs and the a~~lications pmgnm, Pmreedings, First ~nledoMl &,Jercnce on Pauer 

of load equipment, in particular power electronics, Quality: End-Use Applications and Perspectives, Gif-sur-Yvette

Key. T.S. and Sitzlar, H.E.. "Utility compatibility perfomvuxlc 

criteria for end-use equipment,' Proceedings, Open Forum on 

Surge Prorection Application. NISnR 4657, National Institute o

Standards and Technology, 1991, pp: 93-96. 

until such time as voluntary or regulatory standards France. 15-18 ~ctober 1991. pp. 72-78, 

can be fully developed. [I 11 hi, J.S. and Martzloff. F.D.. "Coordinating cascaded surgeprotective devices," Proceedings, IEEE/LS Annual Meeting, 

To that end, all three partners are invited to join October 1991, pp. 1812-1819. 

in improving the family of system compatibility 1121 Ma*loff, F.D. and Ldy, T. E, 'Selecting varistor clamping 

voltage: Lower is not better!" Proceedings. Zirich EMC documents - a growing set of living documents, not Symposium, 1989, pp. 137-142. 

definitive standards - by review and constructive [13] Martzloff. F.D.. "Protecting computer systems against power 

comments addressed to the author of this paper. transients," IEEE Spectrum, April 1990, pp. 3740.