Siemens ACCESS 9340 Reference Manual page 116

ACCESS 9340 and 9360 Meters
Chapter 10—Disturbance Monitoring (ACCESS 9360)
EN–108
A voltage sag is a brief (1/2 cycle to 1 minute) decrease in rms
voltage magnitude. A sag is typically caused by a remote fault
somewhere on the power system, often initiated by a lightning strike.
In Figure 10–1, the utility circuit breaker cleared the fault near plant
D. The fault not only caused an interruption to plant D, but also
resulted in voltage sags to plants A, B, and C.
NOTE: The ACCESS 9360 is able to detect sag and swell events less
than 1/2 cycle duration. However, it may be impractical to have
setpoints more sensitive than 10% for voltage and current
fluctuations.
Figure 10–1: A fault can cause a voltage sag on the whole system
Utility
Transformer
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
ACCESS 9360 can record recloser sequences, too. The waveform in
Figure 10–2 shows the magnitude of a voltage sag, which persists
until the remote fault is cleared.
Utility Circuit
Breakers with
Reclosers
1 Plant A
2 Plant B
3 Plant C
4 Plant D
X
Fault
© 2008 Siemens Energy & Automation, Inc. All Rights Reserved.
PMCM-9340D-0208
2/2008