Schneider Electric PM810, PM870, PM820, PM850 Plant a, Plant B, Transformer Plant C Plant D Fault

PowerLogicTM Series 800 Power Meter					63230-500-225A2
Chapter 9—Disturbance Monitoring (PM870)					3/2011
Figure 9–1: A fault can cause a voltage sag on the whole system
	Utility Circuit
	Breakers with
	Reclosers
Utility				1	Plant A
			2		Plant B
Transformer
				3	Plant C
		X	4		Plant D

Fault

A fault near plant D, cleared by the utility circuit breaker, can still affect plants A, B, and C, resulting in a voltage sag.

System voltage sags are much more numerous than interruptions, since a wider part of the distribution system is affected. And, if reclosers are operating, they may cause repeated sags. The PM870 can record recloser sequences, too. The waveform in Figure 9–2shows the magnitude of a voltage sag, which persists until the remote fault is cleared.

Figure 9–2: Waveform showing voltage sag caused by a remote fault and lasting five cycles

With the information obtained from the PM870 during a disturbance, you can solve disturbance-related problems, including the following:

•Obtain accurate measurement from your power system

—Identify the number of sags, swells, or interruptions for evaluation

—Accurately distinguish between sags and interruptions, with accurate recording of the time and date of the occurrence

—Provide accurate data in equipment specification (ride-through, etc.)

•Determine equipment sensitivity

—Compare equipment sensitivity of different brands (contactor dropout, drive sensitivity, etc.)

—Diagnose mysterious events such as equipment malfunctions, contactor dropout, computer glitches, etc.

—Compare actual sensitivity of equipment to published standards

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