Question

Q.1: Choose the correct answer (and expalin) for the follwoings:

1. Minimum number of coils for 400 V, 6-pole lap connected de machine for a maximum voltage of 15 V between adjacent commutator segments should be

(a) 80 (b) 160 (c) 200 (d) 400

2. The armature resistance of a 6-pole lapp wound de machine is 0.05 Q. If the aramture is re-wound using a wave winding, then the armature resistance will be

(a) 0.452 (b) 0.30 (c) 0.15 (d) 0.102

3. A cumulative compound wound motor runs at 1,200 rpm on no load. When the flux increases by 14% on full load, the full load drop in armature comes to be 5%. What is the full-load speed?

(a) 1,000 rpm (b) 1,332 rpm (c) 1,428 rpm (d) 972 rpm

4. A DC motor has a no-load speed of 6,000 rmp when connected to a 120 V dc supply. The armature resistance is 2.52 and other losses may be neglected. The speed of the motor, when supply voltage of 60 V developing a torque of 0.5 Nm, is

(a) 3,000 rpm (b) 2,673 rpm (c) 2,836 rpm (d) 5,346 rpm

(5) In a transformer

(a) both OC and SC tests are conducted on the Iv side.

(b) Oc test is conducted on hy side and the SC test on lv side.

(c) Oc test is conducted on lv side and the SC test on hy side.

(d) both OC and SC tests are conducted on the hv side.

(6) In a transformer core, third and fifth harmonic components of fluxes are respectively 10% and 4% of the fundamental flux. The third and fifth harmonic induced emfs in the winding, in terms of the fundamental induced emfs are respectively

(a) 30%, 20%

(b) 10%, 12%

(c) 50%, 20%

(d) 50%, 12%

Answer 1