1) Design a neat and suitable sketch of a 3-point starter for a DC shunt motor and describe how the motor is protected against overloads and loss of supply voltage.
2) Design the external characteristics of various types of DC generators. Describe the reason for the shape of each characteristics.
3) What is meant by voltage regulation in the transformer? Find a simple expression for the same by using suitable phasor diagram. Also deduce the conditions for maximum and zero regulation.
4) Two 100 kVA, 1-phase transformer have maximum efficiency of 98% at UPF. In one transformer, maximum efficiency occurs at full-load whereas in the other it occurs at half full-load. Each transformer is on full load at 0.9 pf for 4h, half load at 0.8 pf for 8 h and one0tenth load at 0.7 pf for 12h a day. Find out the all day efficiency of each transformer.
5) A 400 V, delta connected, 3-phase induction motor has stator and rotor standstill impedances of (4+j10)Ω and (3+j10) Ω/ph respectively, values being referred to stator phase. Motor takes a line current of 3.5A at normal voltage on no-load. Compute the following by using the approximate equivalent circuit. For operation at a slip of 5%
(i) line current
(ii) power factor
(iii) developed torque and
(iv) gross efficiency.