GE Grid Solutions Multilin 9450 - 1.8 Power Quality

1–14 EPM 9450/9650 ADVANCED POWER QUALITY METERING SYSTEM – INSTRUCTION MANUAL
POWER QUALITY CHAPTER 1: THREE-PHASE POWER MEASUREMENT
1.8 Power Quality
Power quality can mean several different things. The terms “power quality” and
“power quality problem” have been applied to all types of conditions. A simple
definition of “power quality problem” is any voltage, current or frequency deviation
that results in mis-operation or failure of customer equipment or systems. The causes
of power quality problems vary widely and may originate in the customer equipment,
in an adjacent customer facility or with the utility.
In his book Power Quality Primer, Barry Kennedy provided information on different
types of power quality problems. Some of that information is summarized in Table 1.3.
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
themselves 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.
Table 1.3: Typical Power Quality Problems and Sources
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 voltage,
long-term duration
Non-linear loads
System resonance