Exam Question

(a) Explain the purpose of interpoles and state their magnetic polarity relative to the main poles of both generators and motors. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows; armature (Including brush contact) 0.15 ohm, series field 0.025 ohm, interlope field 0.028 ohm, shunt field (including the field-regulator resistance) 0.115 ohm. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load.