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Q4. a) Explain the potential hazards if liquid-cooled transformers are used. (6)
b) What are the losses in transformers? Mention the various factors which affect these losses. In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. losses are respectively 350 and 400 Watts. Calculate the efficiency at half-full load 0.8 power factor. (10)

Q5. a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque? (6)
b) A three phase, six pole, delta connected induction motor is supplied at 380 V, 60Hz. It draws a current of 45 A at a power factor of 0.85 lag. The stator losses are 4 kW and the windage and friction losses total 3 kW. It runs at 19 rev/s. Calculate EACH of the following:
a) the rotor copper loss. (3)
b) the shaft output power. (4)
c) the shaft output torque. (3)

Q6. A) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star- delta conversion equation can be derived. (6)
b) Three identical coils are delta connected to a 3 ph, 440V, 60 Hz supply and consume a total power of 9 kW at a power factor of 0.8 lag.
a) Calculate the resistance and inductance of EACH coil. (5)
b) If the same three coils are now connected in star to the same supply, calculate the current in each line if: (i) one coil is short circuited; (ii) one coil is open circuited. (5)