General Classes of Power Quality Problems

The terminology presented here reflects recent U.S. and international efforts to standardize definitions of power quality terms. The IEEE Standards Coordinating Committee 22 (IEEE SCC22) has led the main effort in the United States to coordinate power quality standards. It has the responsibilities across several societies of the IEEE, principally the Industry Applications Society and the Power Engineering Society. It coordinates with international efforts through liaisons with the IEC and the Congress Internationale des Grand Réseaux Électriques a Haute Tension (CIGRE; in English, International Conference on Large High-Voltage Electric Systems).

U.S. power industry efforts to develop recommended practices for monitoring electric power quality have added a few terms to the IEC terminology. Sag is used as a synonym to the IEC term dip. The category short-duration variations is used to refer to voltage dips and short interruptions. The term swell is introduced as an inverse to sag (dip). The category  long-duration variation has been added to deal with American National Standards Institute (ANSI) C84.1 limits. The category noise has been added to deal with broadband conducted phenomena. The category waveform distortion is used as a container category for the IEC  harmonics, interharmonics, and dc in ac networks phenomena as well as an additional phenomenon from IEEE Standard 519-1992, Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, called notching.

The categories and their descriptions are important in order to be able to classify measurement results and to describe electromagnetic phenomena which can cause power quality problems.