Electrical Machine MCQs

A 250 V dc shunt motor has an armature resistance of 0.2 and a field resistance of 100 .  When the motor is operated no-load at rated voltage, it draws an armature current of 5A and runs at 1200 rpm. When a load is coupled to the motor, it draws total line current of 50A at rated voltage, with a 5% reduction in the air-gap flux due to armature reaction. Voltage drop across the brushes can be taken as 1V per brush under all operating conditions. The speed of the motor, in rpm, under this loaded condition, is closet to:

a single-phase, 4KVA, 200V/100V,50 Hz transformer with laminated CRGO steel core has rated no-load loss of 450W. When the high voltage winding is excited with 160 V,40Hz sinusoidal ac supply, the no-load losses are found to be 320 W. When the high voltage winding of the same transformer is supplied from a 100V,25 Hz sinusoidal ac source,the no-load losses will be  

a three phase,50 hz, 4 pole induction motor runs at no load with a slip of 1% with full load, the slip increases to 5%. The % speed regulation of the motor is

 Flash point of transformer insulating oil should be more than

The short circuit test in a transformer is performed on