Assignment Three Phase Transformer

Electrical and Electronics Engineering

Electrical Machines II

Assignment 2: Three Phase Transformers



  1. Explain in brief about the construction of three phase transformer.
  2. Draw all the vector group of transformer connection.
  3. Discuss in brief about the application of the four basic types of connections of three phase transformer.
  4. Discuss about the open delta connection and derive that the power transfer capacity is reduced by two third.
  5. Explain about the scott connection. How three phase to two phase transformation is done?
  6. Explain the parallel operation of the three phase transformers.
  7. Discuss the harmonic phenomenon for three phase transformer.


Three 1100/110 V transformers connected in delta-delta supply a lighting load of 100kW. If one of the transformer is out of service, determine the following:

  1. Current of each transformer in healthy condition.
  2. Current of each transformer when one transformer is out of order.
  3. kVA rating of each transformer if it supplies full load in open delta connection.

A 400 kVA load at 0.7 power factor lagging is supplied by three single phase transformers connected in ∆-∆ each. Each transformer is rated at 200 kVA, 2300/230 V. If one defective transformer is removed from service, calculate for the V-V connection,

  1. kVA load carried by each transformer.
  2.  Percent rated load carried by each transformer.
  3.  Total kVA ratings of transformer bank in V-V.
  4. Ratio of V-V bank to  ∆-∆ bank transformer ratings.
  5. Percent increase in load on each transformer when one transformer is removed.

Electric Supply System

The conveyance of electric power from a power station to consumers’ premises is known as electric supply system. An electric supply system consists of three principal components viz., the power station, the transmission lines and the distribution system.
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