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Electrical Engineering Interview Questions

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Regarding three phase supply

Asked By: RAJNEE RANJAN | Asked On: Dec 26th, 2012

Why 440 volt 3 -phase power supply is showing neutral as phase and phase as no supply? As still the power is supplied to the load and its working?

Answered by: rajkiran on: Apr 9th, 2014

in unbalanced loads, i.e., one phase has more load compared to rest of two phases. at that time the loaded phase voltage is low compared to rest of two phases. the difference in voltage is shown at neutral.

Why stones are used in switch yard ?

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

Answered by: daulat on: Apr 2nd, 2014

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

Answered by: ravikumar on: Mar 28th, 2014

To reduce the heat effect

Calculation of electrical cable size

Asked By: Prabakaran Balaraman | Asked On: May 6th, 2011

Will u please give the formula, for selection of cable sizing (both copper and aluminium) depend upon the electrical loads...

Answered by: ENGR.MUHAMMAD YOUNAS KHAN on: Mar 24th, 2014

CABLE SIZING FORMULA:-2 *L * I/(K*Vd) ...............FOR SINGLE PHASE LEGEND:- I :- LOAD CURRENT =160 AMPS L :- LENGTH OF THE CABLE = 200 METERS K :- CONDUCTIVITY OF COPPER = 58 AND CONDUCTIVITY OF...

Answered by: mahmoudp1 on: May 3rd, 2012

It depends on a lot of factors like current density for mm^2 temperature is the cable on cable trays or buried or inclosed in PVC is that a 3 phase cable multicore or what and also depends on the voltage but in general making a current density 2 A/mm^2 for copper for simple applications is good.

DC voltage frequency

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

What is the frequency of DC voltage?

Answered by: shivam gupta on: Mar 19th, 2014

ITS ARBITARY. AND DEPENDS ON THE REQUIREMENT, SUPPOSE THERE IS A SIGNAL= 5+ 3*SIN(2*pi*t) ..... THEN WHAT IS THE FREQUENCY OR TIME PERIOD OF THIS SIGNAL?..... answer- T.P for sinusoidal signal i...

Answered by: Biswajit on: Jan 22nd, 2014

in AC we have different magnitude at different places , but if we will go for DC there is no change in magnitude, so that there will be no matter of cycle, so the value of frequency is zero

DC motor amature control

Asked By: amektk | Asked On: Mar 9th, 2010

Why armature control is used, not the field control for DC motors?What is the drawbacks in field control method?

Answered by: chiragmistry on: Mar 14th, 2014

In case of the dc motor the armature control mathod is used blow the based the motor is run below the based speed Because,above based speed motor react as generator.

Answered by: AHORDZI ERIC on: Nov 20th, 2013

What is ammeture reation

What happens if DC supply is given to a transformer?

Asked By: siva.k | Asked On: Mar 13th, 2013

Answered by: chiragmistry on: Mar 14th, 2014

When DC supply applied to transformer the rate of change of flux is zero so output voltage iz zero.Thats why transformer is not work on dc supply.

Answered by: adarsh on: Mar 2nd, 2014

transformer has high inductance and low resistance. in dc supply there is no inductance only resistance will act in the circuit so high current will flows through the primary of the transformer. for this reason coil and insulation will burn out.

How to generate a sinusoidal wave form?

Asked By: srinu08 | Asked On: Sep 5th, 2013

Answered by: chiragmistry on: Mar 14th, 2014

its very simple connect the capacitor and inductor in series.

Answered by: abhinay on: Sep 20th, 2013

In our tutorials about Electromagnetism, we saw how an electric current flowing through a conductor can be used to generate a magnetic field around itself, and also if a single wire conductor is moved...

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

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

Answered by: praveen on: Mar 5th, 2014

because there is two winding 1 is starting and another is running winding, so that the capacitor is connected to starting winding and to makes its self starting.

Answered by: asmaa radwan on: Feb 8th, 2014

to start induction motor by increasing starting torque

Virtual ground

Asked By: kakarakuka | Asked On: Mar 3rd, 2014

While supply voltage 12v, when I adjust 17v to circuit,my virtaul ground potential become about 0.9v.Why this happening ? Is virtual circuit always zero potential ? Thanks for your helps.

Star/delta transformer

Asked By: s_balwant | Asked On: Feb 5th, 2014

What is neutral transformer?

Answered by: Alok Behera on: Feb 12th, 2014

If the earthing transformer on the Delta Side is outsides the Zone of protection the Earth Fault(E/F)in the delta system outside Current Transformer(CT) locations would produce current distributions a...

Cable

Asked By: kumar_rakesh02 | Asked On: Jul 14th, 2008

What is the difference of h.T and l.T. Cables ?

Answered by: RAHUL LOHIYA on: Feb 5th, 2014

GENRETION TRANSMISSION DISTRIBUSTION

Answered by: sanket on: Oct 2nd, 2013

L.T. means low tension use for below 1000 volts normally pvc cables
H.T. means high tension cable use for more then 1000 volts normally are xlpe shielded cables

Phase and neutral

Asked By: srinu08 | Asked On: Sep 17th, 2013

What is the difference between phase and neutral?

Answered by: billaragu on: Jan 29th, 2014

phase is a electron carrier but neutral is not carrier(earth supply only)......

Answered by: mukesh on: Jan 26th, 2014

phase is refer to high potential line and neutral refers to low potential line ,so charge or current is moving from high potential to low potential..

72v DC motor with two 12v wind generators

Asked By: Alejandro Robles Rivas | Asked On: Jan 10th, 2014

Hello, I have two 12v DC wind generators that can provide charge to a 72v battery bank. This bank is used to power a 72volt electric motor. I have one connected to the first battery (the positive connect for the entire bank) and the other generator is hooked up to the other or last battery of the 72v...

What will happen if we apply DC volt across transformer?

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

Answered by: M.KARTHIKEYAN on: Dec 31st, 2013

First of all a Transformer designed to AC supply only. They required a AC supply to function operation. In case of AC supply: There is a Alternating Flux produced in primary winding. This chang...

Answered by: gangadas on: Feb 1st, 2012

as we know DC is of zero frequency ,and the current is uniform ,no change in current associated with the wdg turns, therefore flux would be zero...

Capacitor and condensor

Asked By: kanchan13 | Asked On: Apr 22nd, 2008

What is the difference between a capacitor and a condensor?

Answered by: ripplenwinder on: Dec 10th, 2013

There is no difference with the exception or semantics and argument. Tesla use to call a capacitor a condenser we now call a condenser a capacitor. Schematics symbol for both are the same!

Answered by: Pruthvi on: Oct 21st, 2013

Main diff. b/w Condensers and capacitors are
i. Condensers are rotating while capacitors are static
ii.Smooth flow in KVAR can be obtained through condensers while it cannot be obtained through switching capacitor banks.

Car alternator is a 3 phase generator.

Asked By: mahmoudp1 | Asked On: May 1st, 2012

In the car alternator is a 3 phase generator and rectified instead of using DC generator. why AC alternator is better than DC generator in any car?

Answered by: ripplenwinder on: Dec 10th, 2013

No! 3 phase has no rectifier or voltage regulator a car alternator does. DC the voltage and current are suppose to be 180 degrees out of phase from one another or so most people think. Current can go ...

Answered by: suryatejreddy on: Apr 12th, 2013

DC generator although produces a.c,it must be converted to d.c by rectifiers in order to store in the batteries and to it supply must be dc,so in cars instead dc generators alternators are used.

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: ripplenwinder on: Dec 10th, 2013

Currents direction (currents phase) and a voltages potential and polarity (+/- or voltages phase) have no constraints to which direction and phase they can travel. Therefore in system with 2 or more ...

Answered by: faraz ahmed on: Mar 12th, 2013

The current flow is dependent on the magnitude of load, when the two systems are synchronized that means you have made a single source of greater capacity so the loads will be shared by this single source and according to their respective magnitudes, that is why current flow takes place.

Why can't the frequency be 100 hz for electricity?

Asked By: aswin_singh | Asked On: Apr 4th, 2013

Answered by: ripplenwinder on: Dec 10th, 2013

In power transmission it cant due to EFIENCY and COST. The higher the frequency the more it is essentialy a direct current! so 100HZ has more power loss due increased current lower peak voltages at th...

Answered by: T.Prasad on: Nov 2nd, 2013

According to indian standards we should maintain frequency as 50hz .since we havebeen designing the equipments for 50hz supply only and we are operating all the power stations in parallel mode and con...

Explain about polarities ?

Asked By: srinu08 | Asked On: Oct 30th, 2013

Answered by: on: Dec 10th, 2013

Polarization is a complex subject? But is easiest understood to me a position, location, direction, depth and etc. from a center point of refrence it is easiest understood by ceating a sphere around t...

Answered by: Yasser Ali on: Nov 1st, 2013

Polarity may refer to: In science: Polarity (mutual inductance) Polarity (physics), a physical alignment of atoms Cell polarity, differences in the shape, structure, and function of cells Chemical po...

3 phase induction motor

Asked By: Yasser Ali | Asked On: Nov 1st, 2013

prove : average power = instantaneous power in 3 phase induction motor

Answered by: ripplenwinder on: Dec 10th, 2013

We can define the 3-phase voltages as: 1) v1 = Vp x sin(u); 2) v2 = Vp x sin(u +120); 3) v3 = Vp x sin(u -120) 4) vn^2 = v1^2 + v2^2 +v3^2 = K 5) sin(u +/- v) = sin(u)cos(v) +/- cos(u)sin(v); 6) sin^...

Answered by: ripplenwinder on: Dec 10th, 2013

Good guestion Ill get back to you on that one.

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