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Other Power Quality Issues-
Voltage Variation,Voltage Steps,Voltage fluctuations andLoad currents
RAJ MOYAL
EE-084022
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CONTENT
WHAT IS POWER QUALITY
PQ PROBLEM
WHY PQ IS SUCH A BIG PROBLEM
VOLTAGE VARIATIONS
VOLTAGE STEPS
VOLTAGE FLUCTUATIONS
LOAD CURRENTS
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WHAT IS POWER QUALITY
The term Power quality is used
to describe the extent of
variation of the voltage, current
and frequency on the power
system. The variation of voltage
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Power Quality problems
Definition.
P.Q. problems is any power problemmanifested in voltage , Current ,orfrequency deviation that result infailure or miss operation of Costumerequipment.e.g.
Surges and spikes (overpowering).
Harmonics ( current & voltage )
Voltage Fluctuations.
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Why PQ is such a Big Problem?
The sensitivity of todays electronicequipment makes it susceptible to
power disturbances.
For some devices, a momentarydisturbance can cause
scrambled datainterrupted communications
system crashes and equipment failure
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Voltage Variations
It is slow variation in rmsvoltage,mainly due to the daily loadvariations.
Types of voltage variations-
- - Sag
- - Interruption- - Overvoltage
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Sag a decrease in RMS voltagelasting
from a half-cycle to a few seconds.
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Interruption complete loss of
voltage.
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Overvoltage an RMS increase involtage
lasting more than a few seconds.
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Voltage Variation Sources
Supply side variations
Short circuits
Capacitor switching Load switching
Regulator malfunction
Load side variations
Motor starting
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VOLTAGE EVENTS
DISTURBANCE EFFECT
Overvoltage Overstress insulation
Under voltage Excessive motor current
Unbalance Motor heatingInterruption Complete shut-down
Sag Variable speed drive & computertrip-out
Swell Overstress insulation
Fluctuations Light flicker
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Voltage Steps
It is sudden change in rms voltagedue to transformer tap changeroperation,load switching
situation,and switching of shuntcapacitors and inductors.
Voltage steps exceeding a certainthreshold need to be considered inany performance criterion.
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Voltage Fluctuations
It is change in rms voltage on a veryshort time scale(seconds or less) due tofast variations in the load current.
It will lead to variation in the intensityof lightning,a phenomena called lightflicker.
Light flickering exceeding certain level
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Well defined standards have beendeveloped to determine whether acertain voltage fluctuation will leadto light flicker:the so called
flickermeter concept.
As voltage fluctuations are due toload variations,responsibility restswith customer behind the loadvariations.
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Load Currents
Current disturbance,both variations andevents is a problem when they do notlead to any voltage
disturbance.e.g.reactive component ofthe current.
This will lead to an increase in losses in
the system,and(variation in rms)requires overratings of seriescomponents like cables and
transformers.
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THANKS