Electrical Engineering: Electrical Machine MCQ

A belt -driven DC shunt generator running at 300 RPM delivers 100kW to a 200 V DC grid.It continues to run as a motor when the belt breaks, taking 10kW from the DC grid. THe armature resistance is 0.025Ω, field resistance is 50Ω,and brush drop is 2v. Ignoring armature reaction, the speed of the motor is ____RPM 

The power input to a 500V,50Hz. 6-pole 3-phase induction motor running at 975 RPM is 40 kW. the total stator losses are 1kW. If the total friction and windage losses are 2.025 kW.then the efficiency is ____% 

The load shown in the figure is supplied by a 400 V (line-to-line) 3-phase source (RYB sequence). The load is balanced and inductive, drawing 3464 VA. When the switch S is in position N, the three watt-meters W 1 , W 2 and W 3 read 577.35 W each. If the switch is moved to position Y, the readings of the watt-meters in watts will be:

A separately excited DC generator supplies 150 A to a 145 V DC grid. The generator is running at 800 RPM. The armature resistance of the generator is 0.1  . If the speed of the generator is increased to 1000 RPM, the current in amperes supplied by the generator to the DC grid is ______.

A 375 W, 230 V, 50 Hz, capacitor start single-phase induction motor has the following constants for the main and auxiliary windings (at starting): Zm = (12.50 + j15.75)Ω (main winding), Za = (24.50 + j12.75)Ω (auxiliary winding). Neglecting the magnetizing branch, the value of the capacitance (in μF) to be added in series with the auxiliary winding to obtain maximum torque at staring is ______