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Electrical Engineering Interview Questions

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Electrical machines

Asked By: gguruprakash27 | Asked On: Jul 25th, 2014

Why we are preferring 4 pole alternator in the production of electric power instead of 2 pole alternator ?

Answered by: s.asokan on: Jul 28th, 2014

Speed is depend on number of poles and frequency. Commomnly all motors are used 1500 RPM and Indian standrad frequency 50hz also motor used 4 pole. In rare case nearly 3000 RPM (high speed motors, ht alternators) machines are used 2 poles.

Answered by: RAKESH KUMAR GHOSH on: Jul 28th, 2014

Because, speed is inversely proportional to number of poles for synchronous machine.

Why voltage is always a multiple of 11 ?

Asked By: rajneesh chaudhary | Asked On: Jul 19th, 2014

Answered by: dhanraj meena on: Jul 25th, 2014

Because the value of from factor is 1.11

Answered by: Gaurahari kuanr on: Jul 20th, 2014

In r.m.s system, form factor is 1.1

What will happen if we apply DC volt across transformer?

Asked By: dhirendra singh | Asked On: Jul 21st, 2007

Answered by: Shashank Lohia on: Jul 24th, 2014

Transformer coils are generally designed with a very high inductance and low resistance values. When DC voltage is applied to the primary of transformer, the change in flux would be zero, so no voltag...

Answered by: NIKKI on: Jul 17th, 2014

If dc is applied to transformer than produced flux will be constant so there will not be any induced emf in primary and secondary so there will not be any opposition to primary flux and a huge current will flow and wdg will get damage

Why the supply frequency in india is 50hz

Asked By: madhulathaoshapaka | Asked On: Jul 17th, 2014

Answered by: liyakath shaik on: Jul 24th, 2014

the  frequency  is  depends  on  speed   synchronous  speed= 120f/p  from this  we  know  that f= Np/120 in  india  speed  of alternator is  nearly  about  3000  rpm  and  the  p...

Sc test

Asked By: goel1982 | Asked On: Feb 3rd, 2010

Why sc test is performed on lv side?

Answered by: KM Mahesha on: Jul 22nd, 2014

Load are in LV side and also max SC faults occurred in Load side. If SC Faults occurs protect load and Net work system

Answered by: vasu on: Jul 21st, 2014

Generally we are conducting sc test on low voltage side because meter protection

Transformer design and construction

Asked By: PRASAN KUMAR PADHY | Asked On: Jul 6th, 2014

What is shape of the coils used in a transformer ? Choose the correct one from the bracket (rectangulAR,oval,circulAR,cylindrical ) & justify it with detail reason. is transformer a machine ?Choose the correct one from the bracket (yes/no) & justify it with detail reason.

Answered by: manikandan.l on: Jul 18th, 2014

Rectangular

Answered by: AlHussein Abdallah on: Jul 16th, 2014

Star connected rotor of induction motor has a standstill impedance of (0.4+4j)ohm per phase and rheostat impedance per phase is (6+2j)ohm. The motor has induced voltage of 80v between slip-rings at st...

At what condition a synchronous motor acts as a synchronous condenser?

Asked By: madhulathaoshapaka | Asked On: Jul 17th, 2014

Answered by: SAHID on: Jul 17th, 2014

A synchronous motor can be referred as a synchronous condenser when is connected in the power system unloaded simply means allowed to rotate freely to correct the system PF

Electrical interview question

Asked By: Kutubuddin Molla | Asked On: Oct 12th, 2011

1)what is the latest generation of circuit breakers called? 2)what are the special cables required for explosion proof wiring? 3)what are the different types of soft starters for large motors? 4)what is the similarity and what is the difference between relays and plc?

Answered by: ayrton on: Jul 8th, 2014

Programmable logic controller is abbreviated as PLC. It is a sort of micro controller used in industrial environment. It is highly resistant to environmental factors such as dust, humidity etc. Howe...

Answered by: Krunal R on: Apr 14th, 2012

1. SF6 Circuit Breaker

Why is the transformer rated in kva?

Asked By: bernard | Asked On: Sep 6th, 2007

Star Read Best Answer

Editorial / Best Answer

Answered by: NagaseshaReddy.M

Answered On : Sep 10th, 2007

kVA is the unit for apparent power. Apparent power consists of active and reactive power. Active power is the share of the apparent power which transmits energy from the source (generator) to the user. Reactive power is the share of the apparent power which represents a useless oscillation of energy from the source to the user and back again.

It occurs when on account of some »inertia« in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only, regardless of whether it aligns with the voltage or not.

Therefore the heat is always proportional to the square of the current amplitude, irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.

Answered by: kalyan sundar dalai on: Jul 5th, 2014

Transformer loss depends on voltage & current and its efficiency is depends its losses obviously its rating in kva.

Answered by: RITU on: Jul 4th, 2014

An efficiency of the transformer depends on core loss(related to voltage) and copper loss(which relates to current), and that does not depend on power factor so the transformers are rated in volt ampere

Explain about brush and brushless alternators ?

Asked By: Lawrence Didy Ebirim | Asked On: Aug 18th, 2011

Answered by: rathod abhishek on: Jul 5th, 2014

Brush is used for collecting current for commutator and send to rotor and rotor rotate . in brush less alternator there is no need of brush....

Answered by: Udhayakumar on: Jul 1st, 2014

NO

DC voltage frequency

Asked By: sintayew | Asked On: Nov 9th, 2009

What is the frequency of DC voltage?

Answered by: RITU on: Jul 4th, 2014

0 HZ

Answered by: vinay vishwakarma on: Jul 1st, 2014

There is no freq. in dc vtg.

Suggest me how to get electrical jobs or relevant jobs ?

Asked By: Smita G | Asked On: Jul 2nd, 2014

Hello sir/madam, i have completed be in electrical with 65% aggregate.Even after trying for many jobs I didnt get desired job so currently am working in bpo sector. So suggest me to get good job related to my educational background please....

Phase identification

Asked By: elexengg | Asked On: Mar 24th, 2009

In a three phase system three wires are of colour red, yellow and blue are used to discriminate each phase. Now how will you identify each phase wire without knowing the colour and without any pre information?

Answered by: Walt Slade on: Jun 30th, 2014

As I said above, there are devices that use a reference and GPS clocks. For example the EDM AP-30 can be touched onto an energized, unlabelled wire and it will display the degrees leading/lagging from...

Answered by: prem on: Jun 29th, 2014

When there no color code how to know r y b and how to test it

Impedance matching

Asked By: Divya Jyothi | Asked On: Jun 24th, 2014

Explain briefly about impedance matching and how the transformer serves in impedance matching?

What is main function of capacitor in single phase induction motor?

Asked By: krunal prajapati | Asked On: Feb 22nd, 2013

Answered by: Vinay vishwakarma on: Jun 16th, 2014

1. to develop starting torque.
2. to split phase upto 90 degree.

Answered by: manoj on: Jun 15th, 2014

Capacitors are used in1single phase induction motor to maintain pf ;no voltage drop .1single induction motor is not a self stating .the net torque in 1 phase motor is zero .by connecting capacitor at supply side required can obtained get started.

Why stones are used in switch yard ?

Asked By: pankaj rawal | Asked On: Aug 14th, 2011

Answered by: zeeshan on: Jun 14th, 2014

To breal the step potential

Answered by: daulat on: Apr 2nd, 2014

1.to reduce wetness
2.to raise resistance
3. avoid grass grow up
4. decrease ground potential.

2 phase winding of induction machine

Asked By: Basireddy Malakondareddy | Asked On: Jun 7th, 2014

If we take the winding displacement as 180 degrees in 2 phase winding what will happen?

Answered by: Himang on: Jun 9th, 2014

Non uniform torque will be produced which would make the operation noisy.

Transformer reactive power

Asked By: mansoor_vm | Asked On: Jul 1st, 2010

Though transformer consist winding which usually cause reactive power change in both generator and motor but it wont affect reactive power passing through transformer why?

Answered by: Dnyanesh on: Jun 7th, 2014

In rotating motor, power factor can not be maintain at unity bcz these all are inductive, but in case of transformer, we can maintain the power factored at unity, and whenever pf is unity, there will be zero reactive power

If two systems are synchronized by having their voltage magnitudes, frequencies and phase synchronized, how does current flow as it can flow only in case of potential difference?

Asked By: prateektaneja | Asked On: Feb 25th, 2013

Answered by: ilamurugan on: May 4th, 2014

Both source becomes single source of higher capacity and at the time of syn only entities are taken for reference. Once syn done its.single.source so need of current flow within that source

Answered by: atul sudhakar on: May 2nd, 2014

In that case ,current flows due to the difference in load angle. synchronizing the system increases the efficiency of the power flow

Induction motor rotation

Asked By: sintayew | Asked On: Dec 16th, 2009

How we can change the direction of rotation of induction motor?

Answered by: atul sudhakar on: May 2nd, 2014

By interchanging the two terminals keeping the third one fixed (fix R terminal and interchange Y and B)

Answered by: Pardeep Sharma on: Dec 29th, 2012

Simply change the phase sequence of any two wire.

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