Electrical Engineering Interview Questions

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What is the different between CGS system and MKS system?

• Oct 10th, 2019

In cgs system is measured in Centimeter ,Gram,Second
In mks system is measured in Meter ,Kilogram ,Second

Henry Grey

• Dec 21st, 2016

But for example, I have 13,600 kg m-1, how much is that in the CGS system of unit? What is the difference (For example: 1 kg = 1000 grams - I want a similar equation for conversion of MSK - CGS units)

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How does a generator generate reactive power

Does it absorb reactive power when ever it is needed ?

Scott Munnings

• Sep 17th, 2018

A machine is run overexcited when VARs are needed by the house load or the grid. Running overexcited up to the machines rating is not necessarily a bad thing. VARs needed to magnetize other machines...

Scott Munnings

• Sep 17th, 2018

Yes. It is measured for both metering (billing) and protective relaying purposes.

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Electrical Power Factor 0.4

If you are an electrical engineer in a factory what will you do if you found power factor 0.4?

Abhijeet

• May 18th, 2018

To improve power factor
1 start capacitor bank it will improve power factor immediately.
2 many industries use synchronous motor (condenser) to improve power factor. It has excellent features to improve power factor. Ns=120f?p by changing frequency(field excitation) hare krishna

Pavan kumar

• Oct 31st, 2017

We use syn. Condensers to improve the power factor

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anass mugdam

• Apr 29th, 2018

The frequency of a system is dependent on the active power balance. As frequency is a common factor throughout the system, a change in active power demand at one point is reflected throughout the sys...

Rockhy

• Dec 2nd, 2011

Frequency means Cycles Per Second ...So to Maintain Phase Difference of 120 degree between three phase to achieve Perfect Sine Wave Frequency Should Remain Constant ..if we dont Maintain the Constant Frequency then there will Be Fluctuation in Voltage as Voltage Is Directly proportional to frequecy

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Transformer Performance

What is the primary impact on the transformer performance if more than the rated KVA load is put on the transformer?

Prakash

• May 9th, 2018

Primary circuit breaker will be blown out, also reclosure could damage at grid.

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MOHAMMED MUZAMMIL

• Apr 1st, 2018

So net voltage in the primary winding will be (Vin-0) more due to which primary winding draws more current which leads to burning of winding. ... But when a particular High DC voltage is applied to th...

• Sep 13th, 2017

Windings get burned

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Electric Voltage AC

for 3 phase AC supply Frequency= 50Hz, V =440 between 2 phase; then V = ? between phase and netural.

Bijit Maitra

• Mar 6th, 2018

254.04V Exactly

Anoar Hossain

• Jan 15th, 2017

254V

Code
1. 1v1nn

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What is the power ratio between power in Star and Delta circuit? Read Best Answer

Editorial / Best Answer

KaranSorout Profile Answers by KaranSorout Questions by KaranSorout

• Member Since Jul-2006 | Jul 13th, 2006

The power ratio between Star to Delta is 1:3

Explanation:

Let?s suppose Vs be the supply voltage per phase.

So the line voltage of the supply will be ?3Vs.

Now assume any type of load; for simplicity I?m assuming it a only resistive load.

And let it be ?R? per phase.

For Delta connected load:

Calculation for per phase power; PD= I2R

Where I ? load current (per phase)

And,

I = ?3Vs/R       {as line voltage of the supply is directly applied to the phase of the delta load}

So,

Pd = (?3Vs/R )2R = 3Vs2/R  watts per phase.

For 3 phases:

P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.

Now for Star connected load:

PS = I2R = (Vs/R)2R = Vs2/R watts

For 3 phases: P3S = 3PS = 3 Vs2/R watts

Conclusion:

P3S / P3D  =  3Vs2/R / 9Vs2/R = 1/3

It may be better concluded by drowing figures. If any variations, can connect to me through karan.sorout@gmail.com

RUP KAMAL KUTUM

• Feb 2nd, 2018

Well first you assumed voltage per phase as Vs and Line voltage as sqrt(3) x Vs: Which is for star connection. Then, you assumed the same thing for Delta Connection(where line and phase voltages are t...

Anbumozhi R

• Dec 3rd, 2017

Power is Same. Whether it is star to Delta conversion or Delta to star conversion. Power is 1:1

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Derating factors for Cables Calculation

The cable's actual current rating will usually be lower than the standard (un-derated) value quoted by manufacturer’s brochures. How to find the Derating factors for depth of laying, grouping of cables, etc.

kkpk

• Feb 19th, 2018

There are seven factors for findout the derating factor value. they are temperature correction factor, ground temperature correction factor, cable distance correction factor, cable depth correction fa...

Mohhamedibrahim

• Dec 21st, 2016

Derating factors
1. Native soil of thermal resistivity
2. If Cable circuit to cable circuit crossing.
3. Wrong sheath bonding.

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For a 100kw generator, only 50kw of load is connected. Will the generator generate only 50kw or 100kw? If it generate 100kw what happens to rest of the 50kw. What happens if we connect more than 100kw of load? Read Best Answer

Editorial / Best Answer

• Dec 23rd, 2006

100 kw is the full load rating of the generator..... ..that means it can supply 100 kw without exceeding in specified temperature limits .that doesnt mean that it wont be able to supply a load more than 100 kw,it can but not for a longer period of time.after sometime the generator will burn out.if a load of 50 kw is connected to generator the generator will generate only 50 kw& not more than that.the generator will generate power only according to the requirement.

Dharmender

• Feb 7th, 2018

Connected Load is 96kw &125kvaDG set will have run stand by unit for Hotel is suitable plz give your technical supporting answer

Mayilsamy Kasipandi

• Jul 11th, 2017

The Generator produce the power is exactly what we withdraw as load. 100 kw genset can produce 1 kw to 115kw power depending upon the connected/withdrawing load. Normally the generator can produce 115% of designed rating.

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Why is the transformer rated in KVA? Read Best Answer

Editorial / Best Answer

• 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.

Raghu

• Feb 9th, 2018

In transformer there is two losses
1. Iron loss
2. Copper loss
The iron loss is depands on Voltage
And the Copper loss is depands on current.

Umar Naik

• Nov 26th, 2017

There are cu losses and iron losses which are not dependent on power factor thats why we rated it in KVA.

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Shona Balaji Santharam

• Jan 1st, 2018

Knee Point Voltage of Current Transformer is the significance of saturation level of a CT core mainly used for protection purposes. The sinusoidal voltage of rated frequency applied to the secondary t...

ravikaurase Profile Answers by ravikaurase Questions by ravikaurase

• Nov 10th, 2010

To know Whether the CT is saturated or not.

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Phase Identification

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?

Soumya Ranjan Nayak

• Dec 28th, 2017

Go for continuity test from source end & at testing end test in discharge condition.

• Nov 22nd, 2017

The neutral is often at the very top of a pole or it could be below the three hot phases. If all the wires are side by side, it sometimes uses a smaller insulator because theres very little voltage on...

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Induction Motor Rotation

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

vidya

• Nov 13th, 2017

What if all 3 phases are interchanged between 3 of them?

atul sudhakar

• May 2nd, 2014

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

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Overall Power Factor of a Panel.

In a panel, I have following loads with respective power factor,
load A - 0.85
load B - 0.8
Load C - 0.9
How to calculate the Overall power factor of the panel, whether I have to take average or I have to consider the lowest?

Michael McCormick

• Nov 3rd, 2017

One needs to know the overall magnitude of each load in addition to power factor. Devolve each load into its real and imaginary components and add them vectorially.

murugan

• Nov 16th, 2016

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DC supply to Transformer

Why the transformer will burn if DC supply is given?

Gajendra Singh

• Oct 30th, 2017

If we apply DC at input end then there will be no emf induced in the primary winding, As e=N*d(flux)/dt. Also leakage reactance (X1)and magnetizing reactance (Xm) will also be zero, coz (X=2f) and f...

saif

• Oct 2nd, 2017

The induced emf in transformer is change of flux linking with number of turns.... if we apply dc to the transformer there is no flux changes in transformer..... emf not induced...mainly winding will be burn

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DC Voltage Frequency

What is the frequency of DC Voltage?

Gaj

• Oct 30th, 2017

Frequency is no. of cycles per second i.e. rate of change w.r.t time. DC has constant amplitude it means no change w.r.t. time. So it has Zero frequency.

Anup Kumar

• Sep 13th, 2017

Zero

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Transformer Voltage Regulation

Which of the following test are to be conducted for the determination of voltage regulation of a transformer.a. Load Testb. Short Circuit Testc. OC Testd. Retardation Test.

SUBHABRATA BASAK

• Oct 9th, 2017

B. Short Circuit Test

SUBHABRATA BASAK

• Oct 9th, 2017

SC Test Only... But also need to know about PF of the Load as V.R. of transformer depends on PF of Load

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Measure Reactive Power

Can we measure reactive power by using only a single wattmeter? If Yes, How?

vki

• Sep 7th, 2017

We can measure by connecting potential coils of two wattmeters between two phases

Vamsi Krishna

• Feb 15th, 2017

Why single wattmeter is enough to measure 3 phase reactive power? Explain it elaborately.

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