1. Armature winding is one in which (a) emf is induced by the leakage flux. (b) emf is induced by the main or working flux. (c) working or main flux is created by the field current. (d) working or main flux is created by the armature current. 2. Armature winding in ac machines (a) is […]
1. In a synchronous machine, if the field flux axis is ahead of the armature field axis in the direction of rotation, the machine operating is (a) synchronous motor. (b) synchronous generator. (c) asynchronous motor. (d) asynchronous generator. 2. The armature of an alternator (a) is a stationary member. (b) is a revolving member. (c)
1. Which of the following conditions is/are necessary for the parallel operation of two transformers? (a) Percentage impedance should be the same. (b) Polarities of both secondaries should be the same. (c) Voltage ratings should be the same. (d) All the conditions mentioned above in (a), (b) and (c) [U.P.S.C. I.E.S. 2011] 2. Conditions for
1. The colour of fresh dielectric oil used in transformers is (a) dark brown. (b) pale-yellow. (c) pale-pink. (d) white-grey. 2. The transformer oil should have (a) low volatility. (b) high dielectric strength. (c) good resistance to emulsion with water. (d) low viscosity to provide good heat transfer. (e) all of the above. 3. Transformer
1. Power transformers are designed to have maximum efficiency around ……… full load. (a) nearly (b) 70% of (c) 50% of (d) 25% of 2. The transformer efficiency will be maximum at a power factor of (a) 0.8 lead. (b) unity. (c) 0.8 lag. (d) 0.5 lag or lead. 3. If P1 and P2 be
1. A 1 kVA, 230/100 V, single phase, 50 Hz transformer having negligible winding resistance and leakage inductance is operating under saturation, while 250 V, 50 Hz sinusoidal supply is connected to the high voltage winding. A resistive load is connected to the low voltage winding which draws a rated current. Which one of the
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1. The primary and secondary windings of a power transformer always have (a) a common magnetic circuit. (b) separate magnetic circuits. (c) wire of same size. (d) same number of turns. 2. If rated dc voltage is applied instead of ac to the primary of a transformer (a) secondary of transformer will burn. (b) primary
1. Which of the following losses occurring in a dc machine has the largest percentage ? (a) Iron loss. (b) Windage loss. (c) Copper loss. (d) Iron loss. 2. Which of the following losses occurring in a dc machine varies significantly with the load ? (a) Armature copper loss. (b) Shunt field copper loss. (c)
1. If the handle of a three point starter goes back to OFF position, it may be due to (a) zero or very low supply voltage. (b) overload. (c) high field circuit resistance. (d) all of the above. 2. A 3 point starter is considered suitable for ………… dc motors. (a) series (b) shunt (c)
1. Consider the following statements regarding speed control of dc motors: Ward Leonard method is suitable for constant torque drive. Field control method facilitates speed control below the base speed. Armature resistance control method is more efficient when compared to Ward Leonard method. Field control method is suitable for constant power drives. Of these statements