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
1. For the same power output rating and full-load speed, the motor that will have poorest starting torque, is (a) cumulative compound. (b) differential compound. (c) series. (d) shunt. 2. A motor used for punching machine is usually subjected to (a) full load continuously. (b) part of full load continuously. (c) no load. (d) intermittent
1. In a dc motor; if armature current is increased, keeping field current constant, the torque developed will (a) remain unchanged. (b) decrease in inverse proportion. (c) increase proportionately. (d) increase in proportion to the square of the armature current. 2. If the supply voltage to a dc shunt motor is increased by 15%, which
1. In an electric motor, the electromagnetic torque developed is (a) in opposite direction to both load torque and frictional torque. (b) in the same direction as the load torque but in opposite direction to frictional torque. (c) in the same direction as the load torque and frictional torque. (d) in the same direction as
1. In the block diagram of a separately excited dc motor, how does the armature induced emf appear as? (a) Positive feedback. (b) Negative feedback. (c) Disturbance input. (d) Output. 2. The current drawn by a 220 V dc motor of armature resistance 0.5 Ω and back emf 200 V is (a) 40 A (b)