A d.c. motor connected to a 460-V supply has an armature resistance of 0.15 ohm Calculate: (a) The value of back e.m.f. when the armature current is 120 A. (b) The value of armature current when the back e.m.f. is 447.4 V.
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A d.c. motor connected to a 460-V supply has an armature resistance of 0.15 ohm Calculate:
(a) The value of back e.m.f. when the armature current is 120 A.
(b) The value of armature current when the back e.m.f. is 447.4 V.
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- A d.c. motor connected to a 460-V supply takes an armature current of 120 A on full load. If the armature circuit has a resistance of 0.25 2, calculate the value of the back e.m.f. at this load.A DC shunt generator delivers 45 A at a terminal voltage of 220 V. The armature and the shunt field resistances are 0.01 2 and 44N respectively. The stray losses are 375 W. What is percentage efficiency of the DC generator4) A dc. ahunt machine while running as generator develops a voltage of 240 V at 1000 rpm. on no-load It has armature resistance of 0.5 12 and field resistance of 250 2. When the machine runs as motor, input to it at no-load ts 4 A at 240 V. Calculate the speed and efficiency of the machine when it runs as a motor taking 40 A at 240 V. Armature reaction weakens the field by 6%
- 1. What do you understand by the term 'back e.m.f.' ? A d.c. motor connected to a 460-V supply has an armature resistance of 0.15 Q. Calculate (a) The value of back e.m.f. when the armature current is 120 A. (b) The value of armature current when the back e.m.f. is 447.4 V. [(a) 442 V (b) 84 A]Which of the following is preferred to counter the effect of armature reaction in DC machine? O Use of main pole OUse of interpoles Use of series winding O Shifting of brushesElectrical Machines Numerical Problems 1. A four-pole, lap wound DC machine is having 500 conductors on its armature and running at 1000 rpm. The flux per pole is 30 m Wb Calculate the voltage induced in the armature winding. What will be induced emf if the armature is rewound for wave winding? (Ans. 250 V, 500 V) 2. A 4-pole machine has an armature with 90 slots and 8 conductors per slot, the flux per pole is 0.05 Wb and runs at 1200 rpm. Determine induced emf if winding is (i) lap connected (ii) wave connected. (Ans. 720 V, 1440 V
- A dc motor having flux per mole of 0.05Wb, 6 ploes containing lap winding with 600 conductors. The motor runs at 500 rpm. The armature resistance is 0.25 ohm and the current drawn by the armature is 40A . Calculate the applied voltage , back emf And armature tourque.2. A d.c. motor connected to a 460-V supply takes an armature current of 120 A on full load. If the armature circuit has a resistance of 0.25 Q, calculate the value of the back e.m.f. at this load. [430 V] 3. A 4-pole d.c. motor takes an armature current of 150 A at 440 V. If its armature circuit has a resistance of 0.15 Q, what will be the value of back e.m.f. at this load ? [417.5 V]A 10 pole lap wound DC armature has a total of 200 conductors each with a current carrying capacity of 10 A. The average induced emf per conductor is 10 V. The power rating of the DC machine is
- The current drawn by a 120 V d.c. motor with back e.m.f. of 110 V and armature resistance of 0.4 ohm is AQ2. A 4-pole, wave-wound armature has 72 slots with two coil-sides per slot, each coil has four turns. If the flux per pole is 20 mWb and the armature rotates at 720 rpm, what is the induced emf across the armature? (Ans. 276.48 V)The armature circuit of a free excited direct current motor with a nominal voltage of 600 V is fed from an adjusted direct voltage source. The excitation circuit is also powered from a regulated voltage source. It is used in an application that requires motor speed adjustment. The speed of the motor at the nominal armature voltage was measured as 1600 rpm. All losses of the motor and voltage source and the effect of armature reaction are neglected. It is accepted that the engine is not saturated.Answer the questions below.a) Draw the armature and excitation circuit of the motor and write the formulas for the equivalent circuit.b) If the load moment of the motor at the nominal armature voltage is 420 Nm, then calculate the armature current and the input power of the motor.c) If the armature voltage of the motor is kept constant at 600 V and the excitation current is decreased until the speed reaches 4000 rpm, then calculate the shaft moment. Show this working area on the M = f (W) axis.