Interview questions with answers- 8

Technical interview question:Give two basic sprrd control scheme of DC shunt motor?

Answer:1. By using flux control method:in this method a rheostat is connected across the field wdg to control the field current.so by changing the current the flux produced by the field wdg can be changed, and since speed is inversely proportional to flux speed can be controlled 2.armature control method:in this method a rheostat is connected across armature wdg.by varying the resistance the value of resistive drop(IaRa)can be varied,and since speed is directly propotional to Eb-IaRa the speed can be controlled.

Technical interview question:what is the principle of motor?

Answer:Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.

Technical interview question:what is meant by armature reaction

Answer:The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

Technical interview question:Give two basic sprrd control scheme of DC shunt motor?

Answer:1. By using flux control method:in this method a rheostat is connected across the field wdg to control the field current.so by changing the current the flux produced by the field wdg can be changed, and since speed is inversely proportional to flux speed can be controlled 2.armature control method:in this method a rheostat is connected across armature wdg.by varying the resistance the value of resistive drop(IaRa)can be varied,and since speed is directly propotional to Eb-IaRa the speed can be controlled.

Technical interview question:what is the difference between synchronous generator & asynchronous generator?

Answer:In simple, synchronous generator supply's both active andreactive power but asynchronous generator(induction generator) supply's only active power and observe reactive power for magnetizing.This type of generators are used in windmills.

Technical interview question:What is the Polarisation index value? Simple definition of polarisation index 

Answer:Its ratio between insulation resistance(IR)i.e megger value for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for motor to be in good condition it should be Greater than 2.5 .