# Power quality phenomenon
# Reasons of power quality
# Effect of power quality
# Terms and Definitions of power quality
1. Introduction
1
What is Power Quality ?
• Quality of electrical service
• Utility, Equipment supplier/Manufacturer,
Consumer
• Power Quality problem:
“Any power problems manifested in voltage,
current, or frequency deviations which results
in failure or misoperation of customer
equipment”
1. Introduction
2
Reasons for Power Quality
1. New-Generation Load Equipment
Microprocessors for Control
Power Electronic Devices
2. Power System Efficiency
Adjustable-Speed Generator/Motor Drive
Shunt Capacitors
3. “Sensitive” Utility Customers
– process controls
– computer power supplies
– electronics of all sorts
4. Interconnected Network Issues
1. Introduction
3
Complicating factors include:
• Utility deregulation
– utility may not be a single entity and problems may
arise at any level
• Distributed generation
- Fuel Cells, Wind power, Photovoltaic power, etc.
– complicates distribution feeder protection and control
– may create power quality issues if not designed well
• Resonance
– unexpected resonances may occur, tending to
exacerbate problems
1. Introduction
4
Causes of Power Quality Problems
Utility Perception
Customer Perception
Neighbor
8%
Customer
25%
Utility
1%
Neighbor
8%
Other
0%
Other
3%
Customer
12%
Natural
Causes
66%
Utility
17%
Natural
Causes
60%
Results of a survey on the causes of
power quality problems by Georgia
Power Company
1. Introduction
5
Causes of Power Quality Problems
Utility Perception
Neighbor
8%
Customer
25%
Utility
1%
1. Introduction
Other
0%
Natural
Causes
66%
6
Causes of Power Quality Problems
Customer Perception
Neighbor
8%
Other
3%
Customer
12%
Utility
17%
1. Introduction
Natural
Causes
60%
7
Reasons for power quality
problems include:
• Switched shunt capacitors
– utility power-factor correction
– customer power-factor correction
• Power system response to faults
– reclosing circuit breakers into faults
– system disturbances of all sorts
1. Introduction
8
power = voltage x current
p(t)  v(t) i(t)
The problem may have several aspects:
1. What is the “quality” of the voltage
supplied to the customer by the utility?
2. What is the “quality” of the current
drawn by the customer?
3. A second customer may see “poor
quality” voltage caused by the utility or
by the first customer or both
1. Introduction
9
Power or Voltage Quality?
• Power=Voltage*Current
– Real Power
– Reactive Power
• Voltage ?
• Current ?
– Short Circuit
– Lightning
– Harmonic Currents
1. Introduction
10
Impacts of Disturbances
• Economic impacts on utility,
customers, equipment supplier
• Equipment damage
• Loss of data
• Manufacturing disruption
• Loss of productivity
1. Introduction
11
How?
1. Introduction
12
Terms and Definitions
2. Terms and definitions
13
IEEE Power Quality Standards
• IEEE SCC-22: Power Quality Standards
Coordinating Committee
• IEEE 1159: Monitoring Electric Power Quality
• IEEE P1564: Voltage Sag Indices
• IEEE 1346:Power System Compatibility with
Process Equipment
• IEEE P1100: Power and Grounding Electronic
Equipment (Emerald Book)
• IEEE 1433: Power Quality Definitions
• IEEE P1453: Voltage flicker
• IEEE 519: Harmonic Control in Electrical Power
Systems
2. Terms and definitions
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IEEE Power Quality Standards
• IEEE Harmonics Working Group
– Single-phase Harmonics Task Force
– IEEE P519A Guide for Applying Harmonic Limits on
Power Systems
– Interharmonics Task Force
– Harmonics Modeling and Simulation Task Force
– Probabilistic Aspects of Harmonics Task Force
• IEEE P446: Emergency and standby power
• IEEE P1409: Distribution Custom Power
• IEEE P1547: Distributed Resources and Electric
Power Systems Interconnection
2. Terms and definitions
15
Categories
1. Transient: impulsive, oscillatory
2. Short Duration Variations: sag, swell,
interruption
3. Long Duration Variations: interruption,
undervoltage, overvoltage
4. Voltage Unbalance
5. Waveform Distortion: harmonics,
interharmonics, DC offset, notching, noise
6. Voltage Fluctuations
7. Frequency Variations
2. Terms and definitions
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Categories
1. Transient
1.1 impulsive
1.2 oscillatory
2. Short Duration
2.1 instantaneous
interruption, sag, or swell
2.2 momentary
interruption, sag, or swell
2.3 temporary
2. Terms and definitions
interruption, sag, or swell
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Categories
3. Long Duration
3.1 interruption (sustained)
3.2 undervoltage
3.3 overvoltage
4. Voltage Unbalance
steady state
2. Terms and definitions
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Categories
5. Distortion
5.1 DC offset
5.2 harmonics
5.3 interharmonics
5.4 noise
6. Voltage Fluctuations
7. Frequency Variations
2. Terms and definitions
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Power Systems Electromagnetic Phenomena
(IEEE Std 1159-1995)
2. Terms and definitions
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Power Systems Electromagnetic Phenomena
(IEEE Std 1159-1995)
2. Terms and definitions
21
2.0 Short Duration Variation
Categories:
Instantaneous
Momentary
Temporary
Types:
Interruption
Sag
Swell
2. Terms and definitions
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Definitions
• Sag (or dip) is a decrease to a low
voltage (between 0.1 and 0.9 per unit
rms) at power frequency for durations
of 0.5 cycle to 1 minute
• Swell is an increase to a high voltage
(between 1.1 and 1.8 per unit rms) at
power frequency for durations of 0.5
cycle to 1 minute
2. Terms and definitions
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