# Electrical Engineering Interview Questions

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#### Input Impedance of Cascade Amplifier

The input impedance of cascade amplifier will :

a. Same as input impedance of first

b. Same as output of second.

c. Same as the entire circuit

d. Same as Stage before the last stage

#### Jayakumar

• Aug 27th, 2021

Same as input impedance of firdt

• Jan 24th, 2016

B. Same as output of second.

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#### 3 PHASE

A three phase motor 20hp with a power factor of 0.85 is to be fed by four single-core, PVC insulated,
copper conductor, non-armoured cables, clipped direct on a non-metallic surface in a confined space
with ambient temperature of 45oC at 40 meter run as shown in Figure Q2. Determine the suitable size
of conductor if the voltage drop from the MCB to the motor terminal must less than...

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#### SALMAN

• May 2nd, 2020

The MKS system is more popular than the CGS system. In measuring force alone the MKS system using newtons as the unit is widely accepted worldwide. Its counterpart in the CGS system is the dyne is sel...

• Oct 10th, 2019

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

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#### VOLAGE CONTOL AND CURRENT CONTROL

What is the difference between volage control device and Current control device

#### ENGINEER: ALJABRBI SALMAN

• May 3rd, 2020

A BJT is a current controlled device because its output characteristics are determined by the input current while a FET is voltage controlled device because its output characteristics are determined by the Field which depends on Voltage applied

#### M SIVARAJ

• Feb 27th, 2020

1.IN VOLTAGE CONTROL DEVICE VOLTAGE WILL BE CONSTANT & CURRENT WILL BE VARY
2..IN CURRENT CONTROL DEVICE CURRENT WILL BE CONSTANT & VOLTAGE WILL BE VARY.

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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

`Code1v1nn`

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#### What is the power ratio between power in Star and Delta circuit?

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.

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.

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 3rd, 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?

• 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

#### 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?

• 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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#### 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.