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 fleld 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115ohm. The Iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)