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CHAPTER 2: ELECTRICAL BACKGROUND
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–17
2.6 Power Quality
2.6.1 Description
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 misoperation
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 the following table.
It is often assumed that power quality problems originate with the utility. While it is true
that may 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 2–3: Typical Power Quality Problems
Cause Disturbance Type Source(s)
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 second or
longer duration
System protection;
Circuit breakers;
Fuses;
Maintenance
Undervoltage/
Overvoltage
RMS voltage, steady state,
multiple second 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