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Technical Interview Materials PDF-Free Download

Technical Interview Q & A PDF

) Which type of oil is used as a transformer oil?

Ans: non-toxic, stable silicon-based or fluoridated hydrocarbons are used, where the added expense of a fire-resistant liquid offsets additional building cost for a transformer vault. Combustion-resistant vegetable oil-based dielectric coolants and synthetic pentaerythritol tetra fatty acid (C7, C8) esters are also becoming increasingly common as alternatives to naphthenic mineral oil.( 

2) what are the points to be consider for MCB(miniature circuit breaker selection?

Ans: 1.25=I(MAX) maximum current. Mcb specification are done on maximum current flow in circuit.

3) What is meant by knee point voltage?

Ans: Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.(CT-current transformer). 

4) What is the difference between isolators and electrical circuit breakers?

Ans: Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault conditions .Actually they used for isolating the CBs for maintenance. Whereas CB gets activated under fault conditions according to the fault detected.( 

5) What are HRC fuses and where it is used?

Answer: HRC stand for “high rupturing capacity” fuse and it is used in distribution system for electrical transformers

6) What is the power factor of an alternator at no load?

Answer: At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor 

7) 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. 

8 ) what is ferrantic effect?

Answer: Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage

9) 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.( 

10) 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 

11) 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. 

12) Give two basic speed control scheme of DC shunt motor?


1. By using flux control method

2. armature control method

13) What is the Polarization index value ?

Ans: Its ratio between insulation resistance(IR)i.e meggar value

14)What is 2 phase motor?

Answer: A two phase motor is a motor with the the starting winding and the running winding have a phase split.


15) What are the advantages of speed control using thyristor?

Answer: Advantages :1. Fast Switching Characterstics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate.

Electronics Communications Questions and Answers: 

1 :: What is the basic difference between latches and flip flops? 

flip flops have clock signal whiles latches dont need any clock pulse.. 2 :: What is race aroun condition in flip flop? 

in a jk flip flop(level triggerd) when J=1,k=1......the 

output Q continuosly keep changing between 1 and 0 as long 

as clock is high.....this is called race around condition. 

3 :: If a crow sit on on current wire it will not fell current but a man touch it he get shock . why? 

1) there is no grond termainal (-ve terminal to complete path),

2) tere is no conductor (conduction medium) In tere leg. 

4 :: Why 2 rectifier is used in smps? 

Its not necessary that a power plant uses only two rectifiers, it depends on the load present at the site and the capacity of the rectifier or SMPS. Suppose the load at the site is 120 Amps and the SMPS capacity is 2000W or the current capacity of the recifier is 50 Amps. In that case 3 or more rectifiers is preffered. Rectifiers is used to balance the load in each phase. 

5 :: What is difference between voltage and potential? 

Voltage is referred as Potenial difference between two points.potential means its force. I think so.voltage defination is 100% correct. 

6 :: Why always current in some amp and voltage is 230? 

current is depending upon the load. ByOhm's law,

V -lR,here load is variable.v-230v so current is depending upon your load 

7 :: Why I hire you and why i dont hire you? 

You should hire me because I meet the eligibility criteria asked by you. Even I had the experience in this relevant field. I am a good team player. For the second question at the end of the interview you will be clear enough of my knowledge and my potential. That will help you to decide whether u sud hire me or not. 

9 :: What kind of modulation is used for land phone communication systems? pulse code modulation 

10 :: What is NMC? network management center 

11 :: what is ups and inverters? 

While both provide backup power during mains outage, with the UPS the switch is instantaneous whereas with the Inverter there is a gap of a second or two. This gap is OK for household gadgets such as lights, fans, fridge, etc. but not OK for computers.

In technical terms: 

UPS: The mains power comes to the UPS. The AC is converted to DC and this DC is constantly charging the battery. The output of the battery is fed to the Sine wave inverter and it converts DC to AC and this feeds the equipment. Since power out is always drawn from the battery, there is no time lag when mains swicthes off; it justs stops the battery from being charged and the UPS continues to supply power till the battery runs out. 

Inverter: The mains power comes to the Inverter. This is directly sent to the output but the AC is also converted to DC and this DC is constantly charging the battery. A sensor and relay mechanism checks whether the mains is ON or OFF. When the main switches OFF, the relay actuator triggers to switch from mains to inverter. Rest is same like the UPS. Because of this sensor and relay, there is a gap between triggering. 

UPS involves more costly circuitary and is therefor more expensive to make and sell. 

12 :: what effect at thersold value on transmission power is increase or decrease in telecommunication? When Transmission power increase the sensitivity of the antenna increase and so the threshold value decrease. 

13 :: what is ups and inverters. and how to give battery connections for ups? ups is a uninterputed power supply.inverter is invet the load in DC to AC than load taking the will be convertor is convet AC to DC that time battery is charged.battery connections in series.. 

14 :: What is operating ratio in railway? Operating Ratio = Total revenue / Total expenses 

15 :: What is artificial intelligence? isnt it is dangerous? an artificial intelligence ic the branch of science which makes the computers to act as an human beings. yes AI is dangerous because it is leading us down to dystopia. it is exploits natural human zoomorphism.

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