Interview questions with answer
Q:Why syn. generators are used for the production of electricity?
A:synchronous machines have capability to work on different power factor(or say different imaginary power varying the field emf. Hence syn. generators are used for the production of electricity.
Q:What is the difference between synchronous generator & asynchronous generator?
A: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.Q:1 ton is equal to how many watts?
A: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.Q:Enlist types of dc generator?
A: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).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 rotary 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 staterQ: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.Q:What will happen when power factor is leading in distribution of power?
A:If their is high power factor, i.e if the power factor is close to one:1.losses in form of heat will be reduced,
2.cable becomes less bulky and easy to carry, and very cheap to afford, &
3. it also reduces over heating of tranformers.
Q:whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?
A:uninterrupt power supply is mainly use for short time . means according to ups VA it gives backup. ups is also two types : on line and offline . online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 12v dc with 7 amp. but inverter is startwith 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup.Q:What is 2 phase motor?
A:A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.
Q:Advantages of vvvf drives over non vvvf drives for EOT cranes?
A:1.smooth start and stop.
2.no jerking of load.
3.exact posiitoning
4.better protection for motor.
5.high/low speed selection.
6.reliability of break shoe.
7.programmable break control.
8.easy circutry
9.reduction in controls
10.increases motor life
2.no jerking of load.
3.exact posiitoning
4.better protection for motor.
5.high/low speed selection.
6.reliability of break shoe.
7.programmable break control.
8.easy circutry
9.reduction in controls
10.increases motor life
Q:What is the significance of vector grouping in Power Transformers?
A:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.Q:Which type of A.C motor is used in the fan (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are find in the houses ?
A:Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run
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