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# Previous Year Exam Questions of Electrical Machines and Power Devices of bput - EMPD by Bput Toppers

• Electrical Machines and Power Devices - EMPD
• 2018
• PYQ
• Biju Patnaik University of Technology Rourkela Odisha - BPUT
• Electronics and Communication Engineering
• B.Tech
• 9947 Views
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#### Previous Year Exam Questions of Electrical Machines and Power Devices of bput - EMPD by Bput Toppers / 3

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e) f) g) h) i) j) Q3 a) b) Q4 a) b) Q5 a) b) Q6 a) b) What will happen if a shunt motor running at no-load has its shunt winding open accidentally? Why starting current of Induction motor is higher than the transformer? Between DC shunt and separately excited generators, whose terminal voltage is high? Justify. Give any two applications of Brushless DC motors. The rotor resistance per phase and standstill rotor reactance per phase of a 3phase IM is 0.2 ohm and 1 ohm respectively. What should be the value of external resistance per phase to be inserted in the rotor circuit to give maximum torque at starting? A 50 Hz, 4 pole , 3 phase induction motor has a rotor current of frequency 2 Hz.Determine (i) the slip and (ii) speed of the motor Part – B (Answer any four questions) A 4 pole lap connected armature of a dc shunt generator is required to supply the following loads in parallel: (i) 5kW Geyser at 250V (ii) 2.5kW Lighting load at 250V. The generator has a resistance of 0.2 ohm and field resistance of 250 ohms. The armature has 120 conductors in the slots and runs at 1000 rpm. Allowing 1V per brush foe contact drop and neglecting friction, find (i) Flux per pole (ii) Armature current per parallel path (iii) total copper loss. With neat diagram explain voltage build up of a shunt generator. (10) (5) A 240 V DC shunt motor runs at 800 rpm and takes armature current of 2 A. Find the resistance required in series with the shunt winding so that the motor may run at 950 rpm when taking an armature current of 28 A. Assume flux is proportional to field current. The shunt field resistance is 160 ohm and armature resistance is 0.4 ohm. Give two disadvantages of this method of speed control. What other methods can be used to control speed of a DC shunt motor? Explain briefly with diagram. Compare DC shunt motor and DC series motor on the basis of Speed ~Armature Current characteristic, Torque ~Armature Current characteristic, Speed ~Torque Characteristic and their applications. (10) A 4 pole, 32 conductors, lap-wound dc shunt generator with terminal voltage of 200volts delivering 12 amps to the load has armature resistance 2 ohm and field resistance of 200ohms. It is driven at 1000rpm. Calculate the flux per pole in the machine. If the machine has to be run as a motor with the same terminal voltage and drawing 5A from the mains, find the speed of the motor. Explain briefly how a single phase induction motor is different from three phase induction motor? (10) A 1-phase, 250/500V, 50 Hz transformer gave the following results: O.C. test: 250 V, 1 A, 80W……… on L.V. side S.C. test: 20 V, 12 A, 100 W ……….. on H.V. side Calculate (i) magnetizing current and the component corresponding to core loss at normalfrequency (ii) the equivalent circuit constants (iii) Draw the equivalent circuit diagram as referred to H.V. side. (iv) Voltage regulation and efficiency at half load and 0.8 pf leading. What are different losses in a transformer? Explain the detailed procedure to determine efficiency of the transformer with neat circuit diagram. (10) (5) (5) (5)

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Q7 a) b) Q8 a) b) Q9 a) b) c) d) The effective resistance of a 1200 kVA, 3.3kV, 50Hz, 3 phase, Y connected alternator is 0.5 ohm between any two terminals. A field current of 35A produces a current of 200A on short circuit and 1.1kV (line to line) on open circuit. Calculate the power angle and voltage regulation when the machine is delivering full load at 0.8 pf lagging. Draw the corresponding phasor diagram. Discuss different methods of starting of synchronous motor. (10) Explain the principle of three phase induction motor. Explain the Torque slip characteristics and derive the condition for maximum torque of a three phase induction motor. Using phasor diagram, derive the expression for power and torque of synchronous motor. (10) Write notes on any THREE : Double field revolving theory Speed control of DC series motor BLDC motor drive circuits Starting methods of three phase induction motor (5) (5) (5 x 3)