Transcript 07_Power Quality

Introduction
 Utilities transmit electricity over power lines into
home as an alternating current (AC) wave.
 This is how power travels through wiring and
passes into appliances.
 Sometimes, interference in the supply of
electricity affects how the equipment runs.
 Many appliances, such as personal computers,
microwave ovens and sophisticated stereo
systems, have sensitive electronics that can be
disrupted or damaged.
 Electric systems experience disturbances from
natural or man-made (e.g., lightning, wind, cars
hitting power poles, falling tree branches, ).
Power Interruptions
 Power interruptions are zero-voltage events on one or
more phases and are typically short duration events, the
vast majority of power interruptions are less than 30
seconds.
 Interruptions can be caused by weather, equipment
malfunction, recloser operations, or transmission
outages.
Interruptions - sources
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Electric supply interruptions are almost always
caused by circumstances external to the
customer's facility.
The leading causes are lightning strikes, damage
to lines usually encountered during inclement
weather, overloaded power lines, and power line
contacts such as birds and trees.
If working on computer, a momentary
interruption can lose data. Avoid this by using a
UPS/battery backup.
Short-term Variations
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Voltage sags
 Sags are a short-term reduction in voltage, and can cause
interruptions to sensitive equipment.
 Voltage sags typically are non-repetitive, or repeat only a
few times.
 causes of sags are the switching on of large loads, or short
circuits on the power line.
 They are also caused by temporary heavy demand for
electricity that exceeds the utilities capability to meet it.
Voltage Flicker
 Voltage flicker is rapidly occurring voltage sags
caused by sudden and large increases in load
current.
 Voltage flicker is most commonly caused by
rapidly varying loads that require a large amount
of reactive power such as welders.
 It can cause visible flicker in lights and cause
other processes to shut down or malfunction.
Transients
 A transient is a "momentary change in the voltage
or current over a very short time.
 More often, transients are measured in
microseconds rather than milliseconds.
 Frequently this transient is called a voltage
"Spike."
Transients - sources
 Lightning is one of the leading causes of transients on
utility power lines.
 The surge currents associated with lightning strikes
interact with the distribution system's impedance creating
voltage transients.
 Lightning can also induce voltages on power lines without
even hitting them. The large electric fields generated
during a discharge can couple into the power system,
creating induced transients.
Transients - solutions
 The solution to transients problems is the
installation of surge protection equipment.
 While some utilities install surge suppression
equipment on their distribution lines it is still
necessary for the customer to install equipment in
their home or business.
 Wiring solutions include using special circuit and
grounding practices.
 Properly designed transmission towers and other
distribution system components can minimize
lightning-generated transients.
Harmonics/Voltage Distortion
 Harmonic is an integer multiple of the fundamental
frequency (60 Hz).
 So, the 2nd harmonic has a frequency of 120 Hz,
the 3rd is at 180 Hz, the 4th at 240 Hz, and so on.
 Voltage distortion is any deviation from the nominal
sine waveform of the AC line voltage.
 Because of the increased popularity of electronic
and other non-linear loads, these waveforms quite
often become distorted.
Harmonics Distortion
 Many solid-state motor controls and computer power
supplies can cause the supply voltage to other equipment to
become so distorted that sensitive electronics will either fail
to operate or operate intermittently.
Power Quality Issue
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Residential area
Heavy Commercial Industry
Light Commercial Industry
Agriculture
Power Quality Issue
 Residential area
 Electronic equipment and
motors are two of the most
common items damaged in a
home.
 Computers, TVs, and stereos
can be damaged by short bursts
of high voltage known as surges.
 Motors like air conditioner
compressors and pumps can be
damaged by high voltage surges
or long periods of very low
voltage.
 Low voltage will cause the
motor to slowly burn up.
Power Quality Solution
 Solutions to power quality problems fall into two
categories;
 i) wiring solutions
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use of special circuit
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grounding practices
 ii) equipment solutions.
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surge suppressors
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power conditioners
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battery backups
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emergency power generators
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voltage regulators