08-08-2012, 01:51 PM
Three Phase Transformers
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A set of three similar single phase transformers may be connected to form a three-phase
transformer (three-phase transformer bank). The primary and secondary windings may be
connected in either star or delta configurations
Three Phase Transformer Bank
1.Three single-phase transformers connected in a three-phase bank.
2. Three sets of windings wrapped on a common core.
Ease of transportation
Inefficient magnetic circuit, less efficient
Higher capital cost than a single one
1-phase of the transformer at fault, the other two are not affected
ertiary Winding
A third set of windings usually exists in 3-phase transformer and used to:
Providing voltage to auxiliary power purposes in the substation or to supply local
distribution system
Power factor correction
Delta connected tertiary windings will provide a circuit for the third harmonics of the
exciting current
Three-phase transformer unit
• Balanced three-phase voltage
• Balanced three-phase flux
• Return leg can be removed
• In-plan construction easy to
• manufacture
• Same operation as transformer bank
Harmonics in Transformer
Harmonics in transformer occur due to the effect of saturation and Hysteresis which are
to produce non-sinusoidal current if the applied voltage is sinusoidal.
Upon saturation, the flux waveform is flat topped and contains mainly 3rd harmonic
component.