Considerable work is under way to establish indices that characterize voltage sag performance and benchmark system performance.



Every two years, industry experts gather at CIRED (Congrès International des Réseaux Electriques de Distribution), an international conference on electricity distribution. The sixteenth annual conference was held in Amsterdam in June. In the last 10 years, power quality has become an increasingly important conference topic. This year, one of the conference's themes focused specifically on power quality and electromagnetic compatibility (EMC). In this month's article, I'll report on some of the important information presented.

The CIRED conference is filled with ample opportunities for attendees to participate in discussions. Tutorials, round table sessions, open discussions, and interactive sessions with the authors of presented papers are provided within a two-day period. Other sessions give invited speakers the chance to summarize important work happening in the industry and allow attendees to make presentations of approximately 5 min. in length.

This year's theme on power quality and EMC was divided into discussion sections on four topics:

  • EMC and safety problems
  • voltage sags and interruptions
  • disturbing loads and phenomena (harmonics, interharmonics, flicker, unbalance)
  • power quality monitoring and new technologies


Each section began with a brief presentation by a keynote speaker, followed by prepared and open discussion periods. Before I summarize the significant details covered in these discussions, let me give one example of the round table sessions.

The Cost of Power Quality

Emmanuel de Jaeger, from Laborelec in Belgium, led one round table discussion on the cost aspects of power quality. Participants in the session made these points:

  • Many customers don't understand equipment sensitivity to power quality variations, which makes it impossible to evaluate the costs of power quality problems.
  • Electricity supply companies must provide information about expected performance that facilities can translate into expected economic impacts.
  • Taking a global perspective when evaluating costs and solutions is essential to identify the most economic alternative for improving performance.
  • Fast transfer-switch technology can be an economic solution on the supply side.
  • Business models for making custom power realistic must include an economic evaluation of costs associated with an expected level of power quality and the benefits of improved power quality.


Voltage Sags and Interruptions

In this area, presenters and attendees discussed the fact that regulations are uncommon, but on the rise. Considerable work is under way to establish indices that characterize voltage sag performance and benchmark system performance. One such index is the System Average RMS Variation Frequency Index (SARFI). These types of guidelines allow customers to perform economic evaluations and develop appropriate equipment specifications.

One conference paper described how the cooperation between Singapore utilities, regulators, and customers is helping them understand and develop solutions to voltage sag problems. An extensive campaign using the SARFI is under way throughout the Singapore grid.

Participants discussed other issues relating to voltage sags, including analytical methods of predicting performance, understanding equipment sensitivity, and characterizing the economics of voltage sags. A number of case studies detailing voltage sag problems and solutions were presented.

On the subject of voltage interruptions, the discussion turned to reliability indices, which deal with the number of interruptions, the duration of interruptions, and unserved energy. Much of the current work in this area deals with tools to predict reliability levels as a function of important parameters and methods for cost/benefit analysis of different investments. Several papers dealt with methods of establishing reliability regulations.

Two papers focused on the cost of interruptions to consumers. This information will help establish reasonable investment guidelines for improving system performance on the supply side. Fig. 2 is from a Greek paper titled, “Interruption Cost Analysis for the Electrical Power Customers in Greece”.

Disturbing Loads

The hot topic in this section was harmonics, which involves the interaction between customer facilities (that create harmonic distortion) and the power system (where harmonic distortion can impact other customers).

Benchmarking current harmonic levels continues to be of utmost importance. A French paper presented harmonics measurement results of 16 low-voltage networks over a one-week period. These measurements illustrated typical harmonic distortion levels experienced by consumers. The fifth harmonic component was the dominant one, and levels between 4% and 5% occur in almost half of the monitored locations. This reflects a 1% increase from a survey conducted in 1991 and offers evidence that a need still exists for regulations on harmonic injection levels, such as the equipment limits specified in IEC 61000-3-2.

An Italian survey presented did not find the same harmonic levels, except in specific circuits supplying public lighting systems.

Voltage fluctuations and flicker also sparked interest because of their interaction issues between customer loads and power system characteristics. A paper from Spain titled, “Connection of a Plant with Arc Furnaces to the Andalucian Network,” presented the results of field measurements that used the methodology from IEC 61000-3-7 to evaluate flicker levels. The author concluded that the limits specified in 61000-3-7 may be unnecessarily strict in this particular case.

Power Quality Monitoring

The main applications for power quality monitoring in Europe continue to be benchmarking campaigns aimed at evaluating compliance with EN 50160. And significant enhancements in data evaluation methods and tools are making these campaigns more efficient and the results more useful. The cost of power quality monitors continues to decline, making large-scale ongoing efforts more realistic. Several papers (France, Belgium) described enhanced applications for permanent power quality monitoring, which help evaluate system performance and specific equipment problems. A paper from Finland did an excellent job describing the integration of power quality monitoring with distribution automation.

Conclusion

CIRED is an excellent technical meeting that gives industry experts the opportunity to discuss important topics with colleagues from around the world. The format provides significant time for discussion, giving all attendees a chance to contribute. Power quality will again be a major theme at the next conference in 2003. I encourage everyone to consider attending or writing a paper for the conference. Abstracts for paper submissions are due a year in advance, so start thinking about your contribution today.

Mark McGranaghan directs power quality projects and product development at Electrotek Concepts. He also works on numerous power quality standards committees. McGranaghan has BS and MS degrees in electrical engineering from the University of Toledo and an MBA from the University of Pittsburgh.