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Dr. Pekik Argo Dahono received the Doctor of Engineering Degree from the Tokyo Institute of Technology, Japan, in He has been with the School of Electrical Engineering and Informatics, Institute of Technology Bandung, Indonesia, since 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 Dahono Institute 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: Phase angle information is lost in both above definitions

Definition of Voltage Unbalance IEC Definition: 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

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 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-Phasing Delta connectionWye connection In practice, the current is increased slightly higher than those values because the power factor and speed are reduced during single phasing

Single-Phasing The motor is easily burning due to Single-phasing on the primary side of transformer.

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

Input Current Waveforms of Six-Pulse Rectifier Balanced condition Input harmonics 6k±1 Unbalanced condition Input harmonics 2k-1

Output Ripple of Six-Pulse Rectifier Balanced conditions Output harmonics 6k Unbalanced condition Output 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

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