USN

1.a)Develop and discuss the equivalent circuit and phasor diagram of a transformer under lagging power factor load.5

b) what is parallel operation? What are the applications and necessary conditions for parallel operation.

5

2.a)Distinguish between distribution and power transformers. 5

b) A 10kVA , 500/250V single phase transformer has maximum efficiency of 94% when delivering 90% of its arted output at unity power factor. Estimate its efficiency when delivering its full load output at power factor of 0.8 lagging

5

3.a)Describe a test to predetermine the efficiency and regulation of two similar single phase transformers connected back to back. 5

b) A 400/ 100V 5kVA, two winding transformer is to be used as an autotransformer to supply power at 400V from 500V source. Draw the connection diagram, show the current distribution and determine the kVA output of the autotransformer. 5

4.a)What is an open delta system? Discuss the features and applications of open delta system.5

b)A 5000kVA, 3 phase transformer 6.6/33kV delta/ star, has a no load loss of 15kW and full load loss of 50kW. The impedence drop at full load is 7%. Calculate the voltage regulation at 3200kW at 0.8 p.f. is delivered at 33kV. 5