Power Quality Basics

Presented by

Scott Peele PE

PQ Basics

Terms and DefinitionsSurge, Sag, Swell, Momentary, etc.

MeasurementsCauses of EventsPossible MitigationPQ ToolQuestions

Power Quality Measurement

Duration (Time) Cycles (.016 seconds per cycle)

Seconds, Minutes, HoursMagnitude (Voltage level)

Transient level I.e. = 1000 voltsRMS - Voltage level i.e. = 120 voltsWaveforms

Distortions

-150

-100

-50

0

50

100

150

0

-200

-150

-100

-50

0

50

100

150

200

0

Magnitude and Duration

60 Hertz/second

DurationTime

Mag

nitu

deV

olta

ge L

evel 169 volts120 Volts RMS

One Cycle .01666 seconds

Terms and Definitions

Transient or Surge SagSwellInterruptionOutageHarmonics

Magnitude and DurationMagnitude and Duration Magnitude and DurationMagnitude and DurationDurationSteadystate Condition

Duration

Transient or Surge Impulse

Transient or Surge oscillatory

SagSwellMomentary InterruptionInterruptionOutageHarmonicsUnbalance

.00000005 -- .002 seconds

.000005 -- .050 seconds

.008 -- 60 seconds

.008 -- 60 seconds

.008 -- 3 seconds3 seconds to 1 MinuteGreater than 1 Minute Steadystate ConditionSteadystate Condition

What is Power Quality & Reliability?

0

100

200

300

400

500

0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100

Time in Seconds

Perc

ent o

f Nom

inal

Vol

tage

Voltage Tolerance EnvelopeApplicable to Single-Phase120-

Volt EquipmentSWELL Region

Outage

Long

Ter

m E

vent

Shor

t Ter

m E

vent

Tran

sien

tSu

rge

Interruptions (<10% of Nominal)

SAG Region

What is a Transient or Surge?A Transient can be classified into two categories, impulsive and oscillatoryDuration < 50 ns to 50 ms

.00000005 seconds to .002 seconds

.000005 seconds to .050 seconds

Impulsive

This is the category that TVSS (Transient Voltage Surge Suppressor) SPD equipment is designed to mitigate.

Sources of Transients

LightningStaticArc Welding

SwitchingcontactorrelaysSCR’s

Oscillatory (Low Frequency)

Capacitor Bank Switch

Substation Bank Line Bank

Voltage Sags

Momentary Interruptions

Breaker Tripped

Outage

Causes of Sag, Interruptions Outages

115 kV Substation

23 k

V Fe

eder

Transformer480 V

Customer

Transformer480 V

Transformer480 V

Transformer480 V

Customer Customer

Customer

Fuse Fuse

Fuse Fuse

Fuse

Fuse

FeederBreaker

Simplified Utility SystemTransmission @ 115 kV

Transformer

Distribution @ 23 kVRegulator

23 k

V Fe

eder

23 k

V Fe

eder

Transformer480 V

Customer

Transformer480 V

Transformer480 V

Transformer480 V

CustomerCustomer

Customer

FuseFuse

FuseFuse

Fuse

Fuse

FeederBreaker

23 k

V Fe

eder

Example

115 kV Substation

23 k

V Fe

eder

Transformer480 V

Customer

Transformer480 V

Transformer480 V

Transformer480 V

Customer Customer

Customer

Fuse Fuse

Fuse Fuse

Fuse

Fuse

FeederBreaker

Simplified Utility SystemTransmission @ 115 kV

Transformer

Distribution @ 23 kVRegulator

23 k

V Fe

eder

23 k

V Fe

eder

Transformer480 V

Customer

Transformer480 V

Transformer480 V

Transformer480 V

CustomerCustomer

Customer

FuseFuse

FuseFuse

Fuse

Fuse

FeederBreaker

23 k

V Fe

eder

Outage

Momentary Interruption

Sag

Time

Quick Trip

6-12 cycles

.3 -

2.0 seconds

13 cycles 15 seconds 35 seconds

lockout

Load Current

FaultInitiated

FaultCurrent

13 cycles

13 cycles

6-12 cycles

6-12 cycles

15 seconds

15 seconds

35 seconds

35 seconds

.3 -

2.0 seconds

.3 -

2.0 seconds

Faulted Feeder

Adjacent Feeder

100%

0%

100%

0%

Voltage

Voltage

FeederBreakerOperation

Substation Voltages During a Feeder Fault

68% Cleared on FirstQuick trip

27% Cleared on Secondand Third Relay

5% Goes to Lock Out

Steadystate Condition Waveform Distortion

HarmonicsInterharmonicsVoltage BalanceOvervoltageUndervoltage

Wave Distortion

Harmonics

Voltage or Current Unbalance =

Maximum Deviation from Average Voltage

Average voltage

243 Volts RMS241 Volts RMS233 Volts RMS

X 100 (for Percent)

239 Average Volts

6239 2.5% voltage unbalanceX 100 =

EXAMPLE

MeasuredVoltages

Customized Solutions

0

100

200

300

400

500

0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100

Time in Seconds

Perc

ent o

f Nom

inal

Vol

tage

Voltage Tolerance EnvelopeApplicable to Single-Phase120-

Volt EquipmentSWELL Region

Outage

Long

Ter

m E

vent

Shor

t Ter

m E

vent

Tran

sien

tSu

rge

Interruptions

SAG Region

TVSS or SPDLine Reactors

Isolation TransformersPower Conditioner

or CVT

UPS

UPS & Genset

IEEE 1159-1995Recommended Practice For Monitoring Electric Power Quality

Table 2 Categories and typical characteristics of power systemelectromagnetic phenomena

Categories Typical Spectral Typical Duration Typical VoltageContent Magnitude

1.0 Transient 1.1 Impulsive 1.1.1 Nanosecond 5 ns rise < 50 ns 1.1.2 Microsecond 1 us rise 50 ns - 1 m s 1.1.3 Millisecond 0.1 m s rise >1 m s 1.2 Oscillatory 1.2.1 Low frequency < 5 k Hz 0.3 - 50 m s 0 - 4 pu 1.2.2 Medium frequency 5 - 500 k Hz 20 us 0 - 8 pu 1.2.3 High frequency 0.5 - 5 M Hz 5 us 0 - 4 pu2.0 Short duration variations 2.1 Instantaneous 2.1.1 Sag 0.5 - 30 cycles 0.1 - 0.9 pu 2.1.2 Swell 0.5 - 30 cycles 1.1 - 1.8 pu 2.2 Momentary 2.2.1 Interruption 0.5 cycles - 3 s < 0.1 pu 2.2.2 Sag 30 cycles - 3 s 0.1 - 0.9 pu 2.2.2 Swell 30 cycles - 3 s 1.1 - 1.4 pu 2.3 Temporary 2.3.1 Interruption 3 s - 1 min < 0.1 pu 2.3.2 Sag 3 s - 1 min 0.1 - 0.9 pu 2.3.3 Swell 3 s - 1 min 1.1 - 1.2 pu3.0 Long duration variation 3.1 Interruption, sustained > 1 min 0.0 pu 3.2 Undervoltage > 1 min 0.8 - 0.9 pu 3.3 Overvoltage > 1 min 1.1 - 1.2 pu4.0 Voltage imbalance steady state 0.5 - 2%5.0 Waveform distortion 5.1 DC offset steady state 0 - 0.1% 5.2 Harmonics 0 - 100th H steady state 0 - 20% 5.3 Interharmonics 0 - 6 k Hz steady state 0 - 2% 5.4 Notching steady state 5.5 Noise broad-band steady state 0 - 1%6.0 Voltage fluctuations < 25 Hz intermittent 0.1 - 7%7.0 Power frequency variations < 10 s

Power Quality Tool

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