Power Quality Standards: An Industry Update

Most of the ongoing work by the IEEE in harmonic standards development has shifted to modifying Standard 519-1992.

Power quality is a worldwide issue, and keeping related standards current is a never-ending task. It typically takes years to push changes through the process. One of the most important developments in the power quality arena is the increased emphasis on coordinating IEEE standards with international standards developed by the International Electrotechnical Committee (IEC). So let's take a closer look at some of the recent developments within these two organizations.

Definitions

The Power Quality Standards Coordinating Committee, SCC-22, sponsored a task force to pull together a list of power quality terms and definitions. However, as the task force began compiling the definitions from various IEEE and IEC standards, they found many confusing or conflicting terms. Despite this hurdle, they tried to identify official definitions and provide examples of properly used terms.

In the end, the group decided to place the document on the Internet and maintain it on an ongoing basis rather than publish a specific standard. You can find this set of definitions on the SCC-22 Web site (http://grouper.ieee.org/groups/1433/).

Power Quality Monitoring

Accurate comparisons of power quality levels from one facility and system to another require consistent methodology. Existing IEEE Standard 1159 provides only general guidelines and definitions, so its group is actively developing more specific procedures for systems monitoring.

Another task force (Standard 1159.3) is working on the development of a Power Quality Data Interchange Format (PQDIF). The format is a means for exchanging power quality monitoring information between different applications. It will allow software developers to design applications that analyze power quality problems independently from the manufacturers of the monitoring equipment. Discussions on the final draft of this standard took place at the IEEE winter power meeting in Columbus, Ohio. Voting will commence sometime soon.

In addition, the task force for IEEE Standard P1159 began a new project that aims to characterize different power quality phenomena and develop guidelines for instrumentation requirements associated with such phenomena. You can expect a draft of these standards by July 1, 2001.

As for the IEC, its members are developing specific standards related to the monitoring requirements for each type of power quality phenomena. For example, IEC Standard 61000-4-7 deals with the requirements for monitoring and measuring harmonics, while IEC Standard 61000-4-15 describes the instrumentation and procedures for monitoring flicker.

The task force for IEC Standard 61000-4-30 plans on providing overall recommendations for monitoring all types of power quality phenomena while still referring to other specific standards where appropriate. IEEE is currently adopting this standardized approach as well.

Voltage Sag and Reliability

Personnel at many utilities monitor voltage sags and calculate indices for system sag performance the same way they do for system reliability. The distribution voltage quality working group for IEEE Standard P1564 is developing recommended indices and procedures for characterizing voltage sag performance and comparing performance across different systems. Undoubtedly, this standardized approach will be extremely useful.

Individual customers can use the voltage sag performance information to evaluate the economics of various alternatives for improving system performance. You can find this evaluation procedure described in IEEE Standard 1346-1998.

Members of IEC SC77A's working group 8 recently wrote an initial draft of IEC Standard 61000-2-8 titled “Environment — Voltage Dips and Short Interruptions.” Its purpose is to describe the expectations and characterizations of system performance. This document warrants considerable discussion within the IEEE to avoid conflicting methods of characterizing system performance in different parts of the world.

Harmonics

Most of the ongoing work in harmonic standards development by the IEEE has shifted to modifying Standard 519-1992. A task force has been organized for this purpose. You can participate in this process through a forum on the Web site at http://grouper.ieee.org/cgi-bin/netforum/ieee519/a/1.

Discussion at the IEEE winter power meeting focused on appropriate limits for harmonic levels inside customer facilities. IEEE Standard 519-1992 provides recommended limits for harmonic levels at the point of common coupling (PCC) between the customer and the power system (i.e., the location where other customers could be supplied). The recommended voltage distortion limit for the PCC is 5% for the total harmonic distortion (THD) and 3% for individual harmonics.

The task force working on the revision to Standard 519 is considering higher limits for inside the facility and making these limits frequency-dependent. The limits specified in IEC for low-voltage systems allow a THD of 8% and include limits for individual harmonic components, which decrease with frequency.

Another group is working on “The Guide for Applying Harmonic Limits on Power Systems,” IEEE Standard 519A. This completed document provides additional application information in conjunction with IEEE Standard 519. It is set to ballot shortly.

Other activities in the harmonics area have task forces working on single-phase harmonic limits and interharmonics issues. These groups will coordinate their efforts with the task force revising Standard 519.

The harmonic filter working group, which is part of the capacitor subcommittee, has recently completed a harmonic filter design guide known as IEEE Standard P1531. This document is currently at the final ballot stage.

A new task force on active filters has been formed under the sponsorship of the IEEE harmonics group. To date, it has produced no draft documents.

Flicker

Developments in voltage flicker standards demonstrate how the industry can successfully coordinate IEEE and IEC activities. IEC Standard 61000-4-15 defines the measurement procedure and monitor requirements for characterizing flicker.

Recent updates to this standard include the response characteristics of incandescent lights on 120V, 60 Hz systems, which permit using the same monitoring equipment to characterize flicker on power systems in North America. The IEEE flicker task force working on Standard P1453 is set to adopt the IEC standard as its own.

Custom Power

The custom power task force working on IEEE Standard P1409 is currently developing an application guide for custom power technologies to provide enhanced power quality on the distribution system. This is an important area for many utilities that may want to offer enhanced power quality services — possibly with special contracts. Look for completion of this application guide within the next year.

Distributed Generation

The new IEEE Standard P1547 will provide guidelines for interconnecting distributed generation with the power system. This standard has been on a fast track and should be balloted shortly. It specifies requirements for the full range of interconnection issues and references appropriate standards for individual power quality issues where appropriate.

For more information on this standard, visit http://grouper.ieee.org/groups/scc21/1547/.

Getting Involved

It's difficult to keep up with the wide variety of power quality standards and guides under development. The best way to stay on top of things is to participate in the process. As power quality professionals, we have the opportunity to increase our participation in these working groups and better coordinate the efforts of the IEC and IEEE. One goal is to have an IEEE participant in each working group, in addition to the IEC national committee representatives. The IEEE's Power Quality Standards Coordinating Committee, SCC-22, is currently looking for individuals to fill some key positions. If you're interested, e-mail Dave Vannoy at [email protected].

Use the table, on page 36, to track down more information and contact the chairmen of task forces that interest you.

IEEE Standards Coordinating Committee

The Power Quality Standards Coordinating Committee, SCC-22, oversees the development of all power quality standards in the IEEE. This committee meets at both the summer and winter Power Engineering Society meetings and at the Industry Application Society annual meeting to coordinate the standards activities underway in each of these groups. Various individual committees that develop the standards, under the leadership of SCC-22, report on their activities in an effort to avoid overlap and conflicts between the societies. SCC-22 also will directly sponsor task forces if a special need arises, and no other appropriate committee can serve this purpose. For instance, SCC-22 sponsors the task force that develops IEEE Standard 1159 for power quality monitoring.

Working Groups of the IEC

The IEC sponsors working groups that develop international standards dealing with all types of power quality issues. These standards are developed under the guidance of Study Committee 77A — Electromagnetic Compatibility. The national committee of each country coordinates the activities of the group participants. For example, Ralph Showers is the Technical Advisor for IEC SC77A on the United States' national committee. There are currently five IEC working groups in IEC SC77A that are developing power quality standards:

Working group 1 — Harmonics and other low-frequency disturbances. This group focuses on limits and methods of measurement for harmonics and interharmonics.
Working group 2 — Voltage fluctuations (flicker) and other low-frequency disturbances. This group works on setting limits for voltage fluctuations caused by customer equipment and methods of appropriate measurement. Members are currently working on an update to the document on reference impedances, which is useful for evaluating the impact of equipment on a system.
Working group 6 — Low-frequency immunity tests. This group develops testing procedures that evaluate equipment immunity from power quality variations.
Working group 8 — Electromagnetic interference related to the network frequency. This group is addressing the full range of power quality phenomena on the network and the interaction issues associated with end users of electricity.
Working group 9 — Power quality measurement methods. This group is currently developing IEC 61000-4-30, an overall guide defining the requirements for power quality monitoring equipment.