Sunday, May 24, 2009

Electrical Interview questions Part 8

Q:What happens if i connect a capacitor to a generator load?
A:Connecting a capacitor across a generator always improves powerfactor,but it will help depends up on the engine capacity of the alternator,other wise the alternator will be over loaded due to the extra watts consumed due to the improvement on pf. Secondly, don't connect a capacitor across an alternator while it is picking up or without any other load.

Q:Why the capacitors works on ac only?
A:Generally capacitor gives infinite resistance to dc components(i.e., block the dc components). it allows the ac components to pass through.

Q:Explain the working principal of the circuit breaker?
A:Circuit Breaker is one which makes or breaks the circuit.It has two contacts namely fixed contact & moving contact.under normal condition the moving contact comes in contact with fixed contact thereby forming the closed contact for the flow of current. During abnormal & faulty conditions(when current exceeds the rated value) an arc is produced between the fixed & moving contacts & thereby it forms the open circuitArc is extinguished by the Arc Quenching media like air, oil, vaccum etc.

Q:How many types of colling system it transformers?
A:1. ONAN (oil natural,air natural)
2. ONAF (oil natural,air forced)
3. OFAF (oil forced,air forced)
4. ODWF (oil direct,water forced)
5. OFAN (oil forced,air forced)

Q:What is the function of anti-pumping in circuit breaker?
A:when breaker is close at one time by close push button,the anti pumping contactor prevent re close the breaker by close push button after if it already close.

Q:what is stepper motor.what is its uses?
A:Stepper motor is the electrical machine which act upon input pulse applied to it. it is one type of synchronous motor which runs in steps in either direction instead of running in complete, in automation parts it is used.