A New IEC Standard on the Measurement of Power Quality Parameters

Following an initiative from the French and the U.S. National Committees, the IEC Technical Committee TC77 charged its Subcommittee 77A (LowFrequency Phenomena) with the development of a new standard on the measurement of power quality parameters. The objectives of this standard, as stated in its scope, are to facilitate and hopefully ensure obtaining reliable, repeatable, and comparable results of power quality parameters, regardless of the compliant instrument being used and regardless of its environmental conditions. The purpose of this paper is to broaden the consensus-building process, beyond the closely-knit TC77 community, toward greater acceptance when the project reaches the final draft voting status. I. BACKGROUND AND EXPECTED BENEFITS The pioneering development of portable power quality monitors, with built-in graphics capability, in the mid1980s triggered intense interest among equipment users concerned with disruption of their operations allegedly caused by poor quality of their electric power supply. Concurrently, increasing dependency on sophisticated electronic controls made the issue even more pressing. The availability of these graphic reports, which became known as "signatures" spurred a new awareness of power quality issues [I]. This interest opened the market to other instrument manufacturers, each developing their own algorithms and software for the measurements of a variety of disturbances, not necessarily based (shared) definitions of these disturbances As a consequence of these independent developments, the resulting survey data have been generally difficult, if not impossible, to compare between two surveys conducted with different instruments. During the initial phases of a new technology development, open competition will generally be a strong and welcome factor to promote innovation, but the result can also become chaotic and counter-productive. A first attempt toward bringing compatibility in this new field was made by the Institute of Electrical and Electronics Engineers (IEEE) in 1987, chartering a working group for the development of a Recommended Practice, which culminated in 1995 with the publication of IEEE Std. 1159 [5]. II. WHAT IS POWER QUALITY ? Asking this question in the year 2000, and after all the work and papers published since the term was first used [6] might seem awkward. However, a brief review of what diverse individuals and organizations mean by "Power Quality" will provide some perspective on the underlying issues, and will show how useful the new IEC standard will be to bring about a shared understanding. In a landmark 1996 decision, the Committee of Action of the IEC approved a recommendation to undertake work on power quality issues as part of the scope of Technical Committee TC77 on Electromagnetic Compatibility (EMC). This decision, recommended by an Ad Hoc Group composed of power quality experts from ten countries, marks an expansion of the scope that will then reach beyond the purely technical issues generally addressed by the EMC community. The IEC Ad Hoc Group considered in 1996 three areas of contributions which an IEC Power Quality Group could make, complementing the work currently done by existing working groups or project teams of TC77: Bringing order to the present chaos of uncoordinated methods of monitoring power quality. Proposing a classification of power quality levels describing what end-users can expect. Building bridges among producers and users of electric power, and equipment manufacturers. Concerns surfaced that undertaking such work might ultimately result in the development and imposition of standards on the quality of "electricity as a productn and create an adversarial relationship. Fortunately, these concerns seem to have receded and a new working group was chartered in 1997 with the specific scope of defining measurement methods "for obtaining reliable, repeatable, and comparable results regardless of the compliant instrument being used and regardless of its environmental conditions." The first Committee Draft (CD) of the IEC document has been circulated in 1999 [7] and resulted in 230 comments from the National Committees. With the concurrence of the IEC Working Group, this paper presents a progress report, identifying major topics and unresolved issues. t Electricity Division, Electronics and Electrical En~ineering Laboratory Technology Administranon. US. De*~artment of Commerce Contributions from the National Institute of Standards and Technology are not subject to U.S. Copyright. Power quality and EMC share many concerns, to the point that each has at some time been described as being a subset of the other. In addition to this fundamental technical aspect, other issues permeate any discussion of power quality. It would be more accurate to draw a multidimension diagram with many overlaps. Also involved are the principals in the transactions, remedial actions, and political implications (see Figure 1). As further illustration of the different perceptions of the power quality concept, Table 1 shows a collection of definitions developed by various standards-writing groups and industry publications. Another illustration of the diversity is Table 2 which shows the terms used in French-speaking countries, in their own national version of French (French being one of the official languages of the IEC) with a literal translation into English.