Power Quality & Energy Efficiency:A Solution to Climate Change

1st POWER QUALITY ASIA CONFERENCE

November 14 & 15, 2012SMX Convention Center, Manila

Dr. Pekik Argo Dahono received the Doctor of Engineering Degree from the Tokyo Institute of Technology, Japan, in 1994. He has been with the School of Electrical Engineering and Informatics, Institute of Technology Bandung, Indonesia, since 1986.He is registered as a Professional Engineer in Indonesia, and as an ASEAN Chartered Professional Engineer. He is a Senior Member of IEEE.At present, he is a chairman of APQI Indonesia.

Effects of Unbalanced Voltage on Electrical Equipment

Pekik Argo DahonoInstitute of Technology Bandung,

Indonesia

Background

• Ideally, a three-phase voltage must be sinusoidal, balanced, and constant frequency.

• Most of electrical equipment have been designed under those assumptions

• Voltage unbalances are usually due to imperfect transposition of transmission and distribution lines, unbalanced loadings due to single-phase loads, and various abnormal conditions.

This Presentations

• Comparing various definitions of unbalance factor

• Examining the effects of unbalanced voltages on three-phase induction motors

• Examining the effects of unbalanced voltages on three-phase rectifiers

• Survey of Voltage Unbalance in Indonesia

Definition of Voltage Unbalance

NEMA (National Equipment Manufacturer Association) definition:

IEEE Definition:

100 voltageline average

voltageline avg thefromdeviation emax voltagVUF%

100 voltagephase average

voltagephase avg thefromdeviation emax voltagVUF%

Phase angle information is lost in both above definitions

Definition of Voltage Unbalance

IEC Definition:

3/2

p

n

3

3

100Vcomponent voltagesequence positiveVcomponent voltagesequence negativeVUF%

je

a

aVVaVV

VaaVVV

cabc2

abn

ca2

bcabp

The above definition is the correct definition but it is difficult to apply in the field as we have to know the line voltage phasors. NEMA and IEEE definitions are usually result in smaller voltage unbalance factors.

Voltage Unbalance Assessment Without Phase Measurements

2

3

23

4

23

4

2

2222

22

22

cabcab

cabcabs

cabcabm

sm

n

sm

p

VVVp

VpVpVppA

VVVA

AAV

AAV

Effects of Unbalanced Voltage on Induction Motors

• Positive sequence results in positive torque

• Negative sequence results in negative torque

• Reducing torque• Reducing speed• Reducing power factor• Increasing losses• Increasing operating

temperature• Reducing efficiency

Equivalent Circuit of Induction Motor

sR lsX

cR mX

lrX

SRr

ps

rsn

s

rsp

SNNNS

NNNS

2fl

lr

p

n

p

n

fl

lr

n

p

II

VV

II

II

ZZ

Current unbalance will be much higher than voltage unbalance

NEMA Derating Factor

Derating is not required if the unbalance factor is less than one percent

Single-PhasingDelta connection Wye connection

In practice, the current is increased slightly higher than those values becausethe power factor and speed are reduced during single phasing

Single-Phasing

The motor is easily burning due toSingle-phasing on the primary side oftransformer.

Rectifiers

A rectifier is used in :- Uninterruptible Power Supplies- Variable Speed Drives- AC and DC power SuppliesVarious methods to reduce input/output harmonics:- Filtering- Multipulsing- PWM techniques

Input Current Waveforms of Six-Pulse Rectifier

Balanced conditionInput harmonics 6k±1 Unbalanced condition

Input harmonics 2k-1

Output Ripple of Six-Pulse Rectifier

Balanced conditionsOutput harmonics 6k

Unbalanced conditionOutput harmonics 2k

Effects of Unbalanced Voltage on Rectifiers

• Low order harmonics are generated on the input and output sides of rectifiers

• These low order harmonics are still generated even under multipulsing or PWM operations

• Passive filters will be too large to minimize these low order harmonics

• Various control methods to minimize these low order harmonics have been proposed in the literature

Survey Results in Depok Area

Survey Results in Presidential Palace

Survey Results in Medan Airport

Survey Results in Bandung Airport

Survey Results in Jakarta Airport

Survey Results in Bandung

Mitigation Methods

• Try our best to distribute evenly single-phase loads among the phases

• Try our best to transpose all transmission and distribution lines

• Provides unbalance protection on motors• Employing SVC or STATCOM to balance the

voltages

Conclusion

• Voltage unbalances are so common in the real world

• IEC voltage unbalance factor can be determined without knowing the voltage phasors

• Unbalanced voltages may create overheating problem in induction motors and harmonic problem in rectifiers

THANK YOU!