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## Sunday, October 30, 2011

### How electrical power is generated by an A.C Generator?

How electrical power is generated by an A.C Generator?
Answer:For the generation of elect power we need a prime mover which supplies mechanical power input to the alternator, can be steam turbines,or hydro turbines .When poles of the rotor moves under the armature conductors which are placed on the stator ,field flux cut the armature conductor ,therefore voltage is generated and is of sinusoidal in nature...due to polarity change of rotor poles(i,e) N-S-N-S.

## Saturday, October 29, 2011

### Why ELCB can't work if N input of ELCB do not connect to ground?

Why ELCB can't work if N input of ELCB do not connect to ground?
Answer:ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that much current will have to return neutral so resultant current is zero. Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence because of this difference in current ELCB wil trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded, fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.

## Friday, October 28, 2011

### What are Motor Generator Sets and explain the different ways the motor generator set can be used ?

What are Motor Generator Sets and explain the different ways the motor generator set can be used ?
Answer:Motor Generator Sets are a combination of an electrical generator and an engine mounted together to form a single piece of equipment. Motor generator set is also referred to as a genset, or more commonly, a generatorThe motor generator set can used in the following different ways:
1.Alternating current (AC) to direct current (DC)
2.DC to AC
3.DC at one voltage to DC at another voltage
4.AC at one frequency to AC at another harmonically-related frequency

### Why series motor cannot be started on no-load?

Why series motor cannot be started on no-load?
Answer:Series motor cannot be started without load because of high starting torque. Series motor are used in Trains, Crane etc.

## Thursday, October 27, 2011

### Why in a three pin plug the earth pin is thicker and longer than the other pins?

Why in a three pin plug the earth pin is thicker and longer than the other pins?
Answer:It depends upon R=rho l/a where area(a) is inversely proportional to resistance (R), so if (a) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and Last to disconnnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

## Wednesday, October 26, 2011

### Why Delta Star Transformers are used for Lighting Loads?

Why Delta Star Transformers are used for Lighting Loads?
Answer:For lighting loads, neutral conductor is must and hence the secondary must be star winding. and this lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.

## Tuesday, October 25, 2011

### What are the advantages of star-delta starter with induction motor?

What are the advantages of star-delta starter with induction motor?
Answer:(1). The main advantage of using the star delta starter is reduction of current during the starting of the motor.Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.

## Monday, October 24, 2011

### what is meant by insulation voltage in cables? explain it?

what is meant by insulation voltage in cables? explain it?
Answer:It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known as insulation level of the cable.

### Why is the starting current high in a DC motor?

Why is the starting current high in a DC motor?
Answer:In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage,Eb = Back emf in Motor,Ia = Armature current,Ra = Aramture resistance).At starting, Eb is zero. Therefore, V=IaRa, Ia = V/Ra ,where Ra is very less like 0.01ohm.i.e, Ia will become enormously increased.

## Sunday, October 23, 2011

### what is ferrantic effect?

what is ferrantic effect?
Answer:Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage.

## Saturday, October 22, 2011

### What is SF6 Circuit Breaker?

What is SF6 Circuit Breaker?
Answer:SF6 is Sulpher hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuitbreaker means SF6 CB.

## Friday, October 21, 2011

### What is the difference between Isolator and Circuit Breaker?

What is the difference between Isolator and Circuit Breaker?
Answer:Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. it is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be made zero and then it can safely operated. its specification only rated current is given.But circuit breaker is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit, overload etc., it is having three specification 1 is rated current and 2 is short circuit breaking capacity and 3 is instantaneous tripping current.

## Thursday, October 20, 2011

### what is power factor? whether it should be high or low? why?

what is power factor? whether it should be high or low? why?
Answer:Power factor should be high in order to get smooth operation of the system.Low power factor means losses will be more.it is the ratio of true power to apperent power. it has to be ideally 1. if it is too low then cable over heating & equipment overloading will occur. if it is greater than 1 then load will act as capacitor and starts feeding the source and will cause tripping.(if pf is poor ex: 0.17 to meet actual power load has to draw more current(V constant),result in more lossesif pf is good ex: 0.95 to meet actual power load has to draw less current(V constant),result in less losses).

## Wednesday, October 19, 2011

### For which device the load current will be maximum? And why?

There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why?
Answer:The motor has max load current compare to that of transformer because the motor consumes real power.. and the transformer is only producing the working flux and its not consuming.. hence the load current in the transformer is because of core loss so it is minimum.

## Tuesday, October 18, 2011

### Tell me in detail about c.t. and p.t. ?(Company:reliance)

Tell me in detail about c.t. and p.t. ?(Company:reliance)
Answer:The term C.T means current transformer,and the term P.T means potential transformer.In circuit where measurements of high voltage and high current is involved they are used there.Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device.so, CT and PT are introduced in the circuits. They work on the same principle of transformer, which is based on linkage of electromagneticflux produced by primary with secondary.They work on the ratio to they are designed.E.g if CTis of ratio 5000\5A and it has to measure secondary current of
8000A.then ANS=8000*5\5000=8Aand this result will be given to ammeter .and after measuring 8A we can calculate the primary current.same is
the operation of PT but measuring voltage.

## Monday, October 17, 2011

### how to calculate capacitor bank value to maintain unity power factor with some suitable example?

how to calculate capacitor bank value to maintain unity power factor with some suitable example?
#e= EXISTING P.F.
#d= DESIRED P.F.

## Sunday, October 16, 2011

### what is stepper motor.what is its uses?

what is stepper motor.what is its uses?
Answer: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.

## Saturday, October 15, 2011

### What is the function of anti-pumping in circuit breaker?

What is the function of anti-pumping in circuit breaker?
Answer: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.

## Friday, October 14, 2011

### How many types of colling system it transformers?

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

## Thursday, October 13, 2011

### Explain the working principal of the circuit breaker?

Explain the working principal of the circuit breaker?
Answer: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.

## Wednesday, October 12, 2011

### Why the capacitors works on ac only?

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

## Tuesday, October 11, 2011

### What happens if i connect a capacitor to a generator load?

What happens if i connect a capacitor to a generator load?
Answer: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.

## Monday, October 10, 2011

### What is the difference between surge arrestor and lightning arrestor?

What is the difference between surge arrestor and lightning arrestor?
Answer: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.

## Sunday, October 9, 2011

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

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

## Saturday, October 8, 2011

### Difference between a four point starter and three point starter?

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

## Friday, October 7, 2011

### What is an exciter and how does it work?

What is an exciter and how does it work?
Answer: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.

## Thursday, October 6, 2011

### What is Automatic Voltage regulator(AVR)?

What is Automatic Voltage regulator(AVR)?
Answer: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.

## Wednesday, October 5, 2011

### Enlist types of dc generator?

Enlist types of dc generator?
Answer:D.C.Generators are classified into two types 1)separatly exicted d.c.generator 2)self exicted d.c.generator, which is further classified into;1)series 2)shunt and
3)compound(which is further classified into cumulative and differential).

## Tuesday, October 4, 2011

### 1 ton is equal to how many watts?

1 ton is equal to how many watts?
Answer:1 ton = 12000 BTU/hr and to convert BTU/hr to horsepower,
12,000 * 0.0003929 = 4.715 hp therefore 1 ton = 4.715*.746 = 3.5 KW.

## Monday, October 3, 2011

### What is the difference between synchronous generator & asynchronous generator?

What is the difference between synchronous generator & asynchronous generator?
Answer:In simple, synchronous generator supply's both active and reactive 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.

## Sunday, October 2, 2011

### Why syn. generators r used for the production of electricity?

Why syn. generators r used for the production of electricity?
Answer:synchronous machines have capability to work on different power factor(or say
different imaginary power varying the field emf. Hence syn. generators r used for the production of electricity.