CHAPTER 2: ELECTRICAL BACKGROUND

2.6Power 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.

Table 2–3: Typical Power Quality Problems

Cause

Disturbance Type

Source(s)

 

 

 

 

 

 

 

 

Lightning;

Impulse

Transient voltage disturbance,

Electrostatic discharge;

transient

sub-cycle duration

Load switching;

 

 

Capacitor switching

 

 

 

Oscillatory

Transient voltage, sub-cycle

Line/cable switching;

transient with

Capacitor switching;

duration

decay

Load switching

 

 

 

 

Sag/swell

RMS voltage, multiple cycle

Remote system faults

duration

 

 

 

 

 

 

 

System protection;

Interruptions

RMS voltage, multiple second or

Circuit breakers;

longer duration

Fuses;

 

 

 

Maintenance

 

 

 

Undervoltage/

RMS voltage, steady state,

Motor starting;

multiple second or longer

Load variations;

Overvoltage

duration

Load dropping

 

 

 

 

 

RMS voltage, steady state,

Intermittent loads;

Voltage flicker

Motor starting;

repetitive condition

 

Arc furnaces

 

 

 

 

 

Harmonic

Steady-state current or voltage,

Non-linear loads;

distortion

long term duration

System resonance

 

 

 

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.

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

2–17

Page 31
Image 31
GE EPM 6000 Multi-function Power Metering System instruction manual Typical Power Quality Problems