IEEE Std 519 revision: the need for probabilistic limits of harmonics

The well-known and ever-present time-varying nature of harmonics in power systems requires a probabilistic treatment which needs to be incorporated in the new IEEE Std 519 revision. This time-varying behavior is due to continuous changes in system configurations, linear load levels and operating modes of nonlinear loads. Recent reviews of other standards have incorporated the time-varying nature on their harmonic limits. The IEC 1000-3-6, for example, uses probabilistic limits for both harmonic currents and voltages. The IEEE 519, however, only mentions the phenomenon. This paper looks at the problems associated with the time-varying nature of harmonics, suggests solutions and ways to deal with the situation based on recent studies and efforts of the IEEE Task Force on Probabilistic Aspects of Harmonics.