# Electrical Engineering Interview Questions

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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,
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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#### Impedance matching

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

#### Navdeep Patil

• Aug 22nd, 2017

You can use Smith chart for impedance matching

#### sandeep

• Oct 28th, 2014

Impedance matching is used to transfer the max. power...transformer serves the purpose of impedance matching by adjusting turns ratio.

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#### iraianbu

• Jul 31st, 2017

In DC circuit, it bypass the unwanted AC signal to the ground

#### Manjula H.G

• Aug 9th, 2006

Bypass capacitance is the property of the capacitor where it blocks DC and allows AC to pass through it. In the sense it allows DC to pass through the circuit.

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#### Neutral ct

Why do we use neutral ct in a transformer?

#### anil kumar

• Jul 24th, 2017

We have not neutral CT in 10/12.5 mva transformer input voltage 132 /33 kv then what would be problem without neutral CT .

#### EEE

• Mar 18th, 2012

A neutral CT is usually connected to the neutral of a star connected transformer. for balanced condition the current through neutral is zero.but if any unbalance occurs such as a ground fault, then th...

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#### Power Main Cable Puncture and Bursting

In a Manufacturing Factory, it is observed regularly the power cables are bursting resulting in fire even though branded cables are used. Identify the cause of bursting and guide to avert any future disaster of cable failure leading to mega fire accident.

#### Mayilsamy Kasipandi

• Jul 11th, 2017

Commonly two reasons.
1. Loose connection in the lug termination or connectors side
2. Cable rating is under capacity

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#### Load Increases when Power Generation is Constant

What happens if load increases when the generation is constant?

#### Mayilsamy Kasipandi

• Jul 11th, 2017

Load increases when power is constant - Result voltage drop depending upon the load

#### Ravi

• Mar 7th, 2017

The excess load draws more current from source. since the the power is constant in source side, voltage on load side drops and losses are more and power factor reduced.

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#### Electrical Ceiling Fan Rotation

Why ceiling fan rotates in anticlockwise direction?

#### P.Raghavan

• Jun 13th, 2017

When fan stops suddenly and starts running in clockwise what is it due to?

#### amardeep singh

• Jul 30th, 2011

Flux is produce in clockwise direction and eddy currents makes fan to rotate in anticlockwise direction..........

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#### Inductance in Transmission Lines

What type of effects are produced in transmission lines due to mutual inductance and due to self inductance?

• Apr 27th, 2017

Answer is both. The primary EMF in transformer is induced by the self induction, whereas the secondary EMF of the transformer EMF is induced by the mutual induction. Here is the main question what pri...

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#### UPF and LPF Wattmeters

How is UPF Wattmeter different from LPF Wattmeter?

#### Siva

• Apr 21st, 2017

LPF Watt meters are specially designed to measure the power at low power factor (inductive circuits).

UPF type Watt meters are not so accurate in measuring power at low factor (resistive circuits).

#### sharath

• Oct 28th, 2011

LPF watt meter is used for measuring power in highly inductive circuits & UPF watt meter is used for measure power in resistance circuit in which the power factor ranges from 0.5 to unity.

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#### Half Controlled and Full Controlled Rectifier

What is the difference between half controlled and full controlled rectifier? Why we go for full controlled while half controlled can control voltage?

#### k.r.kartheeswari

• Apr 10th, 2017

In Half controlled rectifiers, the controlled output will be in one half cycle, so the efficiency is less. But in full controlled rectifies, the controlled output will be in both the half cycle since both the sides having SCRs. So efficiency also doubled compared to half controlled.

• Feb 4th, 2016

Diode is uncontrolled and SCR is fully controlled element. In SCRs we can turn ON and OFF by gate pulse or by the other means. Whenever the diode is used in rectifier, the rectification is done by the...

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#### DC Pulse when applied to Transformer

When DC is applied, Transformer goes in to saturation, What happens if DC Pulses are applied, will this be safe? Will it act as transformer?

• Mar 29th, 2017

If we apply DC to the transformer, the nature of DC is constant magnitude so constant flux generate in primary winding there is no change in flux so EMF will not induce excepting when switch ON and switch OFF. If DC is continually supplied to the primary it will burn.

#### Ravi

• Mar 7th, 2017

When DC applied to Transformers the induced emf is zero in primary because of steady current, which leads to heavy current flow coz only coil resistance is connected directly to the source. Which dama...

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#### DC-DC Flyback Convertor

What is the flyback convertor?

#### Harita

• Feb 18th, 2017

Flyback converter is a buck boost converter used in the SMPS (Switch Mode Power Supply, small size and large frequency)

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