ELECTRICAL QUESTION & ANSWERS(4)

Q1)What is damper winding?

Ans) Synchronous motors are not self-starting therefore to start them a special set of winding known as damper winding is placed on rotor poles. These windings are similar to squirrel cage rotor which consist of short circuited copper bars embedded on the rotor poles.

When Ac supply is given to stator of a 3 phase synchronous motor then it produces rotating magnetic field. Due to damper winding present on the rotor, MACHINE STARTS AS AN INDUCTION MOTOR i.e( Synchronous motor starts as an induction motor and continue to accelerate).

The exciter of a synchronous motor moves along with the rotor and when the motor attains 95% of the synchronous speed then rotor winding is connected to exciter terminals and rotor is magnetically locked by the rotating magnetic field of stator and it runs as synchronous motor

Q2) What is electrical machine?

 Ans) A device which is used for electro-mechanical energy conversion or vice versa is called as an electrical machine. If the device converts electrical to mechanical energy then it is termed as motor, where as if a device converts mechanical to electrical then it is termed as generator. By changing the input-output configuration, same device can work as either generator or motor.

Q3) Why is the capacity of power plant in MW? Why not in MVA OR MVAR?

MW represents the active power, MVA represents apparent power whereas MVAR represents Reactive power. MW describes the actual power that can be supplied to the load whereas MVA represents the actual power supplied to the load plus the circulating power between load and power plant

Secondly, the input power given to power plant is in MW because it is given through primer movers and prime movers output is in HP or MW. Therefore capacity of power plant is in MW

Q4) What is SWITCHING CAPACITY in circuit breakers?

Maximum amount of current that a circuit breaker can interrupt safely without doing any damage to it is called switching capacity of CB.              

Q5) Why there is a better power factor in Synchronous motor than induction motor?

Higher power factor means low requirement of magnetizing current (Im) and also low requirement of MMf for energy transfer.

Since synchronous motor has two excitation: dc and ac excitation. Therefore it reduces machine’s excitation dependency on main supply and hence ensures better power factor. Whereas Induction motor has no such provision, hence low pf.