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Doc# E166703 1-18
1: Three-Phase Power Measurement
It is often assumed that power quality problems originate with the utility. While it is
true that power quality problems can originate with the utility system, many problems
originate with customer equipment. Customer-caused problems may manifest them-
selves inside the customer location or they may be transported by the utility system
to another adjacent customer. Often, equipment that is sensitive to power quality
problems may in fact also be the cause of the problem.
If a power quality problem is suspected, it is generally wise to consult a power quality
professional for assistance in defining the cause and possible solutions to the
problem.
Cause Disturbance Type Source
Impulse transient Transient voltage disturbance,
sub-cycle duration
Lightning
Electrostatic discharge
Load switching
Capacitor switching
Oscillatory
transient with decay
Transient voltage, sub-cycle
duration
Line/cable switching
Capacitor switching
Load switching
Sag/swell RMS voltage, multiple cycle
duration
Remote system faults
Interruptions RMS voltage, multiple
seconds or longer duration
System protection
Circuit breakers
Fuses
Maintenance
Under voltage/over voltage RMS voltage, steady state,
multiple seconds or longer
duration
Motor starting
Load variations
Load dropping
Voltage flicker RMS voltage, steady state,
repetitive condition
Intermittent loads
Motor starting
Arc furnaces
Harmonic distortion Steady state current or volt-
age, long-term duration
Non-linear loads
System resonance
Table 1.3: Typical Power Quality Problems and Sources
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