1. Introduction 1

# Power quality phenomenon

# Reasons of power quality

# Effect of power quality

# Terms and Definitions of power quality

1. Introduction 2

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 3

Reasons for Power Quality

1. New-Generation Load EquipmentMicroprocessors for ControlPower Electronic Devices

2. Power System EfficiencyAdjustable-Speed Generator/Motor DriveShunt Capacitors

3. “Sensitive” Utility Customers– process controls– computer power supplies– electronics of all sorts

4. Interconnected Network Issues

1. Introduction 4

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 5

Causes of Power Quality Problems

Results of a survey on the causes of power quality problems by Georgia Power Company

1. Introduction 6

Causes of Power Quality Problems

1. Introduction 7

Causes of Power Quality Problems

1. Introduction 8

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 9

power = voltage x current)t(i)t(v)t(p

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 10

Power or Voltage Quality?• Power=Voltage*Current

– Real Power– Reactive Power

• Voltage ?• Current ?

– Short Circuit– Lightning – Harmonic Currents

1. Introduction 11

Impacts of Disturbances

• Economic impacts on utility, customers, equipment supplier

• Equipment damage

• Loss of data

• Manufacturing disruption

• Loss of productivity

1. Introduction 12

How?

2. Terms and definitions 13

Terms and Definitions

2. Terms and definitions 14

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 15

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 16

Categories

1. Transient: impulsive, oscillatory2. Short Duration Variations: sag, swell,

interruption3. Long Duration Variations: interruption,

undervoltage, overvoltage4. Voltage Unbalance5. Waveform Distortion: harmonics,

interharmonics, DC offset, notching, noise6. Voltage Fluctuations7. Frequency Variations

2. Terms and definitions 17

Categories1. Transient

1.1 impulsive1.2 oscillatory

2. Short Duration 2.1 instantaneous

interruption, sag, or swell2.2 momentary

interruption, sag, or swell2.3 temporary

interruption, sag, or swell

2. Terms and definitions 18

Categories

3. Long Duration3.1 interruption (sustained)

3.2 undervoltage

3.3 overvoltage

4. Voltage Unbalancesteady state

2. Terms and definitions 19

Categories

5. Distortion5.1 DC offset

5.2 harmonics

5.3 interharmonics

5.4 noise

6. Voltage Fluctuations

7. Frequency Variations

2. Terms and definitions 20

Power Systems Electromagnetic Phenomena (IEEE Std 1159-1995)

2. Terms and definitions 21

Power Systems Electromagnetic Phenomena (IEEE Std 1159-1995)

2. Terms and definitions 22

2.0 Short Duration Variation

Categories:

InstantaneousMomentaryTemporary

Types:InterruptionSagSwell

2. Terms and definitions 23

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