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 cycle.so, in automation parts it is used.

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Electrical Interview questions Part 7

Q:What is Automatic Voltage regulator(AVR)?

A:AVR is an abbreviation for Automatic Voltage Regulator.It is important part in Synchronous Generators, it controls theoutput voltage of the generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator.

Q:What is an exciter and how does it work?

A:There are two types of exciters, static exciter and rotory exciter.purpose of excitor is to supply the excitation dc voltage to the fixed poles of generator.Rotory excitor is an additional small generator mounted on the shaft of main generator. if it is dc generator, it will supply dc to the rotory poles through slip ring and brushes( conventional alternator). if it is an ac excitor, out put of ac excitor is rectified by rotating diodes and supply dc to main fixed poles.ac excitor is the ac generator whose field winding are stationary and armature rotates. initial voltage is built up by residual magnetism.It gives the starting torque to the generator.
 

Q:Difference between a four point starter and three point starter?

A:The shunt connection in four point stater is provided separately form the line where as in three point stater it is connected with line which is the drawback in three point stater

Q:Why use the VCB at High Transmission System ? Why can't use ACB?

A:Actually the thing is vacuum has high arc queching property compare to air because in VCB ,the die electric strengths equal to 8 times of air . That y always vaccum used as inHT breaker and air used as in LT .

Q:What is the difference between surge arrestor and lightning arrestor?

A:LA is installed outside and the effect of lightning is grounded,where as surge arrestor installed inside panels comprising of resistors which consumes the energy and nullify the effect of surge.

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