Transient Surges and Surge Suppressor Technologies: Comparing Apples to Oranges

Jan. 14, 2008
The suppressor to protect a specific point upon an electrical distribution system must be selected according to its physical location.

The sole function of a quality surge suppressor is to protect sensitive electronic equipment from transient overvoltages that are present on AC power circuits. It is irrelevant whether these overvoltages are generated by lightning activity or are induced upon the AC power lines by utility grid switching, power factor correction actions, power cycling of inductive loads, or from other sources. A quality surge suppressor must limit transient overvoltages to values that do not surpass the AC sine wave peak by more than 30% as it initially absorbs intense amounts of transient energy. The suppressor must immediately respond to transients before they reach their uppermost voltage values. Suppressor performance should not deviate or degrade with use when called upon to divert extreme levels of transient current.

Transient surges are differentiated by their duration, frequency and amplitude. The surge suppression industry has adopted IEEE Power Engineering Society’s IEEE C62.41-2002 document, titled IEEE RECOMMENDED PRACTICE ON SURGE VOLTAGES IN LOW-VOLTAGE AC POWER CIRCUITS, as the standard for categorizing transients and the associated waveforms used to test suppressor efficacy. This guide defines several varied voltage and current waveforms that occur in the electrical distribution environment. The most frequently referenced IEEE waveform is the combination wave. The combination wave is characterized by short duration, high-frequency short-circuit 8/20μs and open-circuit 1.2/50μs current and voltage waveforms. It is used to simulate lightning-induced transient activity. Longer duration, lower frequency, higher energy 10/1000μs voltage and current test impulses (also detailed within the same IEEE documentation) are recommended to simulate transient activity originating from other sources. For testing, actual voltage and current values are selected in reference to where the surge suppressor is intended for use. Surge suppressors intended for use at any location on the distribution system will be subjected to long duration waveforms and should be tested to withstand these conditions, regardless of their suppression technology.