Electrical Power Systems Quality

Yiting Zhao yitingzh@buffalo.edu

Chapter 1

Introduction

What Is Power Quality?What Is Power Quality?What Is Power Quality?What Is Power Quality?

Power Quality = Voltage QualityPower Quality = Voltage QualityPower Quality = Voltage QualityPower Quality = Voltage Quality

Why are we concerned about power quality?Why are we concerned about power quality?Why are we concerned about power quality?Why are we concerned about power quality?

The Power Quality Evaluation ProcedureThe Power Quality Evaluation ProcedureThe Power Quality Evaluation ProcedureThe Power Quality Evaluation Procedure

What Is Power Quality?What Is Power Quality?What Is Power Quality?What Is Power Quality?

Any power problem manifested in voltage, Any power problem manifested in voltage, Any power problem manifested in voltage, Any power problem manifested in voltage, current, or frequency deviations that results in current, or frequency deviations that results in current, or frequency deviations that results in current, or frequency deviations that results in failure or misoperation of customer equipment.failure or misoperation of customer equipment.failure or misoperation of customer equipment.failure or misoperation of customer equipment.

What Is Power Quality?

Power Quality = Voltage QualityPower Quality = Voltage QualityPower Quality = Voltage QualityPower Quality = Voltage Quality

P = V IP = V IP = V IP = V I

V--consistentV--consistentV--consistentV--consistent controled by power supply system controled by power supply system controled by power supply system controled by power supply system I --varied by partivular loadI --varied by partivular loadI --varied by partivular loadI --varied by partivular load

Therefore, the standards on the power quality are Therefore, the standards on the power quality are Therefore, the standards on the power quality are Therefore, the standards on the power quality are maintaining the supply voltage within certain limits.maintaining the supply voltage within certain limits.maintaining the supply voltage within certain limits.maintaining the supply voltage within certain limits.

Why are we concerned about Why are we concerned about Why are we concerned about Why are we concerned about power quality?power quality?power quality?power quality?

UtilitiesUtilitiesUtilitiesUtilitiesCustomersCustomersCustomersCustomersSuppliers of load equipmentSuppliers of load equipmentSuppliers of load equipmentSuppliers of load equipment

EconomicEconomicEconomicEconomic

Chapter 2

Terms and Definitions

General Classes of Power Quality ProblemsTransientsLong-Duration Voltage VariationsShort-Duration Voltage VariationsVoltage ImbalanceWaveform DistortionVoltage FluctuationPower Frequency VariationPower Quality Terms

General Classes of Power Quality Problems

For steady-state phenomena, the following attributes can be used: ■ Amplitude ■ Frequency ■ Spectrum ■ Modulation ■ Source impedance ■ Notch depth ■ Notch area

For non-steady-state phenomena, other attributes may be required: ■ Rate of rise ■ Amplitude ■ Duration ■ Spectrum ■ Frequency ■ Rate of occurrence ■ Energy potential ■ Source impedance

TransientsTransientsTransientsTransients

Part of the change in a variable that disappearsPart of the change in a variable that disappearsPart of the change in a variable that disappearsPart of the change in a variable that disappearsduring transition from one steady state operating during transition from one steady state operating during transition from one steady state operating during transition from one steady state operating condition to another.condition to another.condition to another.condition to another.

SurgeSurgeSurgeSurge

Impulsive TransientsImpulsive TransientsImpulsive TransientsImpulsive Transients

An impulsive transient is a sudden, nonAn impulsive transient is a sudden, nonAn impulsive transient is a sudden, nonAn impulsive transient is a sudden, non––––power power power power frequency change in the steady-state condition of frequency change in the steady-state condition of frequency change in the steady-state condition of frequency change in the steady-state condition of voltage, current, or both that is unidirectional in voltage, current, or both that is unidirectional in voltage, current, or both that is unidirectional in voltage, current, or both that is unidirectional in polarity (primarily either positive or negative).polarity (primarily either positive or negative).polarity (primarily either positive or negative).polarity (primarily either positive or negative).

For exampleFor exampleFor exampleFor example 1.2 1.2 1.2 1.2×50-50-50-50-μs 2000-volt s 2000-volt s 2000-volt s 2000-volt (V) (V) (V) (V)

Oscillatory TransientsOscillatory TransientsOscillatory TransientsOscillatory Transients

An oscillatory transient is a sudden, nonAn oscillatory transient is a sudden, nonAn oscillatory transient is a sudden, nonAn oscillatory transient is a sudden, non––––power power power power frequency change in the steady-state condition of frequency change in the steady-state condition of frequency change in the steady-state condition of frequency change in the steady-state condition of voltage, current, or both, that includes both positive voltage, current, or both, that includes both positive voltage, current, or both, that includes both positive voltage, current, or both, that includes both positive and negative polarity valuesand negative polarity valuesand negative polarity valuesand negative polarity values

high-frequency transienthigh-frequency transienthigh-frequency transienthigh-frequency transientmedium-frequency transientmedium-frequency transientmedium-frequency transientmedium-frequency transientlow-frequency transientlow-frequency transientlow-frequency transientlow-frequency transient

Long-Duration Voltage VariationsLong-Duration Voltage VariationsLong-Duration Voltage VariationsLong-Duration Voltage Variations

Long-duration variations encompass root-mean-Long-duration variations encompass root-mean-Long-duration variations encompass root-mean-Long-duration variations encompass root-mean-square (rms) devia-tions at power frequencies for square (rms) devia-tions at power frequencies for square (rms) devia-tions at power frequencies for square (rms) devia-tions at power frequencies for longer than 1 min.longer than 1 min.longer than 1 min.longer than 1 min.

OvervoltagesOvervoltagesOvervoltagesOvervoltagesUndervolt-agesUndervolt-agesUndervolt-agesUndervolt-ages

OvervoltagesOvervoltagesOvervoltagesOvervoltages

An overvoltage is an increase in the rms ac voltage An overvoltage is an increase in the rms ac voltage An overvoltage is an increase in the rms ac voltage An overvoltage is an increase in the rms ac voltage greater than 110 percent at the power frequency for a greater than 110 percent at the power frequency for a greater than 110 percent at the power frequency for a greater than 110 percent at the power frequency for a duration longer than 1 min.duration longer than 1 min.duration longer than 1 min.duration longer than 1 min.

Overvoltages are usually the result of load switchingOvervoltages are usually the result of load switchingOvervoltages are usually the result of load switchingOvervoltages are usually the result of load switching

Undervolt-agesUndervolt-agesUndervolt-agesUndervolt-ages

An undervoltage is a decrease in the rms ac voltage to An undervoltage is a decrease in the rms ac voltage to An undervoltage is a decrease in the rms ac voltage to An undervoltage is a decrease in the rms ac voltage to less than 90 per-cent at the power frequency for a less than 90 per-cent at the power frequency for a less than 90 per-cent at the power frequency for a less than 90 per-cent at the power frequency for a duration longer than 1 min.duration longer than 1 min.duration longer than 1 min.duration longer than 1 min.

A load switching on or a capacitor bank switching A load switching on or a capacitor bank switching A load switching on or a capacitor bank switching A load switching on or a capacitor bank switching off can cause an undervoltage until voltage off can cause an undervoltage until voltage off can cause an undervoltage until voltage off can cause an undervoltage until voltage regulation equipment on the system can bring the regulation equipment on the system can bring the regulation equipment on the system can bring the regulation equipment on the system can bring the voltage back to within tolerances.voltage back to within tolerances.voltage back to within tolerances.voltage back to within tolerances.

Sustained interruptionsSustained interruptionsSustained interruptionsSustained interruptions

When the supply voltage has been zero for a When the supply voltage has been zero for a When the supply voltage has been zero for a When the supply voltage has been zero for a period of time in excess of 1 min, the long-duration period of time in excess of 1 min, the long-duration period of time in excess of 1 min, the long-duration period of time in excess of 1 min, the long-duration voltage variation is considered a sustained voltage variation is considered a sustained voltage variation is considered a sustained voltage variation is considered a sustained interruption. interruption. interruption. interruption.

Voltage interruptions longer than 1 min are often Voltage interruptions longer than 1 min are often Voltage interruptions longer than 1 min are often Voltage interruptions longer than 1 min are often per-manent and require human intervention to per-manent and require human intervention to per-manent and require human intervention to per-manent and require human intervention to repair the system forrepair the system forrepair the system forrepair the system forrestoration.restoration.restoration.restoration.

Short-Duration Voltage VariationsShort-Duration Voltage VariationsShort-Duration Voltage VariationsShort-Duration Voltage Variations

Interruption--Interruption--Interruption--Interruption--a complete loss of voltagea complete loss of voltagea complete loss of voltagea complete loss of voltageSags (dips)--Sags (dips)--Sags (dips)--Sags (dips)--temporary voltage drops temporary voltage drops temporary voltage drops temporary voltage drops Swells--Swells--Swells--Swells--voltage risesvoltage risesvoltage risesvoltage rises

InterruptionInterruptionInterruptionInterruption

An interruption occurs when the supply voltage or An interruption occurs when the supply voltage or An interruption occurs when the supply voltage or An interruption occurs when the supply voltage or load current decreases to less than 0.1 pu for a period load current decreases to less than 0.1 pu for a period load current decreases to less than 0.1 pu for a period load current decreases to less than 0.1 pu for a period of time not exceeding 1 min.of time not exceeding 1 min.of time not exceeding 1 min.of time not exceeding 1 min.

加图P21P21P21P21

Sags (dips)Sags (dips)Sags (dips)Sags (dips)

A sag is a decrease to between 0.1 and 0.9 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

SwellsSwellsSwellsSwells

A swell is defined as an increase to between 1.1 and 1.8 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

加图2.82.82.82.8

Voltage ImbalanceVoltage ImbalanceVoltage ImbalanceVoltage Imbalance

The maximum deviation from the average of the The maximum deviation from the average of the The maximum deviation from the average of the The maximum deviation from the average of the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the average of the three-phase voltages oraverage of the three-phase voltages oraverage of the three-phase voltages oraverage of the three-phase voltages orcurrents, expressed in percent.currents, expressed in percent.currents, expressed in percent.currents, expressed in percent.

Waveform DistortionWaveform DistortionWaveform DistortionWaveform Distortion

A steady-state deviation from an ideal sine wave of A steady-state deviation from an ideal sine wave of A steady-state deviation from an ideal sine wave of A steady-state deviation from an ideal sine wave of power frequency principally characterized by the power frequency principally characterized by the power frequency principally characterized by the power frequency principally characterized by the spectral content of the deviation.spectral content of the deviation.spectral content of the deviation.spectral content of the deviation.

There are five primary types of waveform There are five primary types of waveform There are five primary types of waveform There are five primary types of waveform distortion:distortion:distortion:distortion:

■ DC offset DC offset DC offset DC offset ■ Harmonics Harmonics Harmonics Harmonics ■ Interharmonics Interharmonics Interharmonics Interharmonics ■ Notching Notching Notching Notching ■ Noise Noise Noise Noise

Voltage FluctuationVoltage FluctuationVoltage FluctuationVoltage Fluctuation

Systematic variations of the voltage envelope or a series of random voltage changes, the magnitude of which does not normally exceed the voltage ranges

Voltage Imbalance (voltage Voltage Imbalance (voltage Voltage Imbalance (voltage Voltage Imbalance (voltage unbalance)unbalance)unbalance)unbalance)

The maximum deviation from the average of the The maximum deviation from the average of the The maximum deviation from the average of the The maximum deviation from the average of the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the three-phase volt-ages or currents, divided by the average of the three-phase voltages oraverage of the three-phase voltages oraverage of the three-phase voltages oraverage of the three-phase voltages orcurrents, expressed in percent.currents, expressed in percent.currents, expressed in percent.currents, expressed in percent.

Flicker Flicker Flicker Flicker Pst--short-term flicker sensation Pst--short-term flicker sensation Pst--short-term flicker sensation Pst--short-term flicker sensation Plt--long-term flicker sensation Plt--long-term flicker sensation Plt--long-term flicker sensation Plt--long-term flicker sensation

Power Frequency VariationsPower Frequency VariationsPower Frequency VariationsPower Frequency Variations

Power frequency variations are defined as the deviation of the power system fundamental frequency from it specified nominal value (e.g., 50 or 60 Hz)

Power Quality TermsPower Quality TermsPower Quality TermsPower Quality Terms

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