Problems #3

1. Show the internal connections of three-phase transformers with the following Vector Groups:

(i) Dz0

(ii) Yy6

(iii) Dy1, Yd1

(iv) Dy11, Yz11

2. Explain how a transformer from Group III may be operated in parallel with a transformer from Group IV by changing external connections only.

3. Two identical single-phase transformers are feeding a balanced delta-connected load with unity power factor. Show the phasor diagram for the open-delta connection. How each transformer will share the load?

4. Explain the load sharing of the individual transformer when they are supplying a balanced star-connected inductive load with a power factor of 0.866 lagging.

5. A balanced 3-phase, 100 kW, 400 V load with power factor 0.866 lagging is supplied from transformers connected in open-delta from 11 kV line,

(i) Find the kVA rating of the two transformers and their turns-ratio.

(ii) Determine the line currents on the LV and HV sides.

(iii) What is the real power supplied by each transformer.