## Best And Free Electrical Interview Questions Bank On DC Motor!!

### Interview Questions On Working Principle Of DC Motor

1) define function of DC Motor???
Ans: An electric motor is a machine which converts electric energy into mechanical energy.

2) In d.c. motor conductor is experienced force by whose principle??

Ans: Fleming's Left-hand Rule

3)what is the function of commutator in d.c. motor??
Ans: the function of a commutator in the motor is the same as in the generator. By reversing current in each conductor as it passed from one pole to another, it help to develop a continuous and unidirectional torque.

4) In lathes machine which type of motor are uses???
Ans:shunt type d.c. motor

5)where the  series type d.c motor are used??
Ans:
* For traction work i.e. Electric locomotives
*Rapid transut system
*Trolley, cars etc.
*Cranes and hoists
*Conveyors

6)For intermittent high torque loads which motor are used??
Ans: Comulative compound type d.c. motor

For Get Full Knowledge About The Working Principle Of DC Motor Than Go Now : https://www.theengineeringstreet.com/2018/01/principle-and-working-of-dc-motor.html

### Interview  Questions On Losses in DC Machine

1)list The losses occurring in dc machines ???
Ans: listed as below:
(1) copper losses
(2) Magnetic or iron losses
(3) Mechanical losses
(4) Stray load losses

2) give The various copper losses occurring in the windings ??????
Ans:
(A)  Armature copper loss
(B) Shunt field copper loss
(C) Series field copper loss
(D) Copper loss in interpole winding
(E) Brush contact loss

3)The armature copper loss is about ______% of totle full load losses amd field copper losses are about ______%of full load losses.???
Ans:30-40 and  20-30

4)Magnetic losses is also known as????
Ans:These losses are also called iron loss or core loss.

5)magnetic loss consist which losses???
Ans:Iron losse consists of (1) Hysterisis losses and (2) Eddy current losse.

6)magnetic loss  are about _____of full load losses.???
Ans: 20% to 30%

7)explain hysteresis losses in dc machine???
Ans:Hysterisis losses

This loss is due to reversal of magnetism of the armature core.
These losses pccur in armature core teeth of the dc machine.
Hysteresis losses can be reduced by using core material of silicon steel which has low hysterisis coefficient.

8)define eddy current???
Ans:When armature core rotates in magnetic field of poles it also cuts the magnetic flux. Hence an emf is induce in the body of the core according to the low of electromagnetic induction. This emf set up current in the body of the armature core and its know as eddy current

9)mechanical losses consists which losses???
Ans:(a)  Bearing and brush friction losses
(b)  Winding loss or air friction of rotating armature.
These losses are about 10-20% of totle full load losses.

10)stray losses occurring because of???
Ans:(1)Distortion of flux because of armature reaction
(2)due to eddy current in conductore
(3)short circuit current in the armature coil undergoing commutation.

For Get Full Knowledge About The Losses Of DC Machine Than Go Fast :: https://www.theengineeringstreet.com/2018/02/losses-in-dc-machine.html

### Interview Questions Related To Armature  Reaction

1)The armature magnetic field has how manny effects and which???
Ans: Two
(1) It demagnetises or weakens the main flux and
(2) It cross-magnetises or distorts.

2) what is the full form of G. N. A???
Ans: geometrical neutralaxis or plane(G.N.A.)

3)define Magnetic neutral axis???
Ans: as the axis along which no e.m.f. is produced in the armature conductors because they then move parallel to the lines of flux.

4)what is Leading Pole Tip(LPT)???
Ans:It is the end of the pole which first comes in contact with armature in the direction of rotation by the armature conductors.

5) give the fullform of TPT and define TPT???
Ans:Trailing Poles Tip(TPT)
It is the end of the pole which comes in contact later with the armature in the direction of rotation.

You Want To Know All About The Armature Reaction Than Go Fast :: https://www.theengineeringstreet.com/2018/01/armature-reaction.html?m=1

### Interview Questions On Different Types Of Magnetic Exciting System

1)how many type for Exciting to Magnetic System??
Ans: two type (1) single excited and (2) doubly excited

2)Give the formula of  The incremental electrical energy (dWe)  due to the flow of current in the Single Excited System??
Ans: dW=E.i dt

3)Give the formula For angular movements of armature  the electromagnetic torque for a linear system ???

T=(1/2)*(i^2)*(dL/d§)
Where §=angle

4)What is Doubly Excited Magnetic System??
Ans:A magnetic system which is excited by two independent source is called doubly excited magnetic circuit.

5) Give the example of Doubly Excited Magnetic System??
Ans:The synchronous machines and d.c. machines .

6)Give formula for satisfied the energy conversion principle in Doubly Excited Magnetic System??
Ans: dWe = dWm + dWf

7)Give the formula of Magnetic torque developed in Doubly Excited Magnetic System??
Ans:Tm d§ =(1/2)(i^2) dLs + (1/2)(ir^2) dLr +(is) (ir) dM
Where §=anglr
Ir= rotor current
Is= stator current

Getting Full Knowledge About The Magnetic Excited Systems Than Go Now Fast ::https://www.theengineeringstreet.com/2018/02/different-types-of-magnetic-excited-systems.html

## Here the Difference Between Magnetic And Electrical Circuit !!!

### A) Analogy Between Magnetic And Electric Circuit

• 1)

Magnetic Circuit  :

The Closed Path Followed by The Magnetic Flux Is Called Magnetic Circuit.

Electric Circuit  :

The Path In Which Electric Current Can Follow Is Known As Electric Circuit.

• 2)

Magnetic Circuit :

Flux = MMF / Reluctance

Electric Circuit :

Current = EMF / Resistance

• 3)

Magnetic Circuit :

MMF (AT)
This Is the cause of linking of flux in the circuit.

Electric Circuit :

EMF ( Volts)
This is the cause of flow of electric current in the circuit.

• 4)

Magnetic Circuit :
Flux Density = Flux / Area

Electric Circuit :
Current Density = Current / Area

• 5)

Magnetic Circuit :
Reluctance = This opposes the linking of magnetic flux.

Electric Circuit :
Resistance = This Opposes the flow of electric current.

• 6)

Magnetic Circuit :
Permeance = 1/Reluctance

Electric Circuit :
Conductance = 1/Resistance

• 7)

Magnetic Circuit :
Permeability = 1/ Reluctivity

It is the property of the magnetic path to pass more flux.

Electric Circuit :
Conductivity = 1/ Resistivity

It is the property of the conducting material to pass more current.

• 8)

Magnetic Circuit :
S = S1 + S2 + S3 + ............... + Sn
In series Magnetic Circuit.

Electric Circuit :
R = R1 + R2 + R3 + .................+ Rn
In series electric circuit.

• 9)

Magnetic Circuit :
1/S = 1/S1  +  1/S2  +  ............. +  1/Sn
In parallel Magnetic Circuit.

Electric Circuit  :
1/R  =  1/ R1  +  1/R2  + .............. + 1/Rn
In parallel Electric Circuit.

### B) Differences Between Magnetic Circuit And Electric Circuit

The Magnetic Circuit differs from the electric circuit in the following respects :

(1) Resistance is normally independent of current in an electric circuit, whereas reluctance depends on the Flux Density in the magnetic circuit.

For This reason magnetization (B-H) curves of magnetic materials are used for determining necessary excitation.

(2) Flux actually links in the magnetic circuit, whereas current actually flows in the circuit.

(3) In magnetic circuit, energy is needed to create the magnetic flux only at starting but in an electric circuit, energy is consumed till the current flows.

(4) The magnetic circuit has the property of retentivity .
i.e. a small amount of lux called residual flux persists after the removal of the MMF .

Whereas in an electric circuit, the current reduces to zero after the removal of the applied EMF or when circuit is broken.

## Best And Free Electrical Interview Questions Bank On Transformer!!

### Questions On The Basic Of Transformers

1)What Is the transformer???
Ans:A transformer is a static electromagnetic device consisting of two or more windings which link with a common magnetic field.
• A transformer a device that transfers electric power from one circuit to another without a change of frequency.
• It can raise or lower the voltage in a circuit but with a corresponding decrease or increase current

2)when the output voltage of a transformer is higher than its input voltage, it is called _____???
Ans: step-up transformer

3) what is work of transformer??
Ans:transfers electrical energy from one circuit to another
->does so without a change of frequency
->does so by the principle of electro-magnetic induction
->has electric circuits that are linked by a common magnetic circuit.

4)the winding In to the load from which drawn out is called which winding???

5)A transformer work on the which  principle???
Answer : electromagnetic induction

Read The Theory Concept Of Electrical Transformers https://www.theengineeringstreet.com/2018/02/basic-of-electrical-transformer.html?m=1

### Question On The Types Of Transformers

1)give a type of transformer according to construction?????
Ans: (i) Core type and (ii) Shell type

2)in core type transformer winding on ____??
Ans:the windings surround the iron core.

3) give one advantage of core type transformer???
Ans:As the space utilisation is better with stepped cores, the length of mean turn of copper is reduced and therefore copper losses and cost of copper also reduced.

4)how arrange shell type transformer winding?????
Ans:In shell type transformers, the windings are put around the central limb and the flux path is completed through two side limbs.

5)give one advantage of shell type transformer???
Ans: In this type of transformer, the coils are better braced mechanically that they are less easily displaced by the high electro-mechanical forces that frequently develop during short circuits

Read The Theory Concept On The Types Of Transformers  https://www.theengineeringstreet.com/2018/02/types-of-electrical-transformers.html

Recommended Article

### Questions On Auto - Transformer

1) The Auto Auto-transformer works on the principle of ______???
Ans: self induction

2) in the auto transformer how many winding???
Ans: one

3)what is the transformation ratio of an auto-transformer ????
Ans: k=(V2/V1)=(N2/N1)=(I1/I2)

Read Theory Concept Of Auto - Transformer : https://www.theengineeringstreet.com/2018/02/all-about-ideal-transformers-auto-transformer.html

### Questions On The Consist Of The Electrical Transformers Or Electrical Transformers Parts

(1)Which part consists of cores and yokes and provides path of flux in three phase transformer???
Ans:magnetic circuit

(2) Electric circuit which type of part consists????
Ans:An electric circuit consist a of LV and HV windings. The windings are electrically separated but magnetically linked through a path of low reluctance.

(3)What is the work of dielectric circuit part in three phase transformer???
Ans:. The insulation is provided between LV and HV windings and core to LV winding.

(4)which parts consisting in  Tank and accessories In the three phase transformer???
Ans:This includes cooling system, oil conservator, breather, bushings, Buchholz relay and other protective devices.

(5) what is a work of magnetic circuit in three phase transformer???
Ans:provides path of flux

Read The Theory Of The Consist Of Electrical Transformers Or Parts Of Electrical Transformers https://www.theengineeringstreet.com/2018/03/essential-consist-of-transformer.html

### Questions On The Current Transformer

(1)What is the current transformer????
Ans:A CT is a device for the transformation of current from a higher  values to a lower values that are suitable for measurement of the relay operation.

(2)The VA rating of CTs is ?????
Ans:very small

(3)primary winding of current transformer have how many ternes???
Ans:The primary winding of the CT consists of one or few turns of thick wire

(4)give type of current transformer according to construction!!??
Ans:According to the construction, the CTs can be classified into two ways

(i) Bar primary CTs or single turn CT wound type
(ii) Wound type CT

(5)describe bar type CT??
Ans:In bar primary type CT, he primary is a straight conductor passing through the centre of a hollow core and the secondary has a ring hollow core type iron core on which the wound uniformly over the entire periphery.

(6)short not on wound type CT??
Ans:The wound type CTs have magnetic core. The two windings are wound on a magnetic iron core. The primary winding consists of a few turns of thick wire, they can not be distributed uniformly over the iron core. Therefore wound type CTs have high leakage flux and hence posseses high reactance

### Questions On The Potential Transformer

(1) what is Potential transformer?????
Ans: potential transformer  are used for the uannformation of voltage from higher values to a lower values.

(2)Potential transformers are used for ?????
Ans:meaaurement and protection.

(3)potential transformer winding consist of few turns of thick wire and is called which winding??
Ans:The secondary winding

(4)which is the primary winding of the potential transformers???
Ans:which have  relatively large number of turns of thin wire and is called primary winding.

(5)For lower voltages up to 3.3kv which type potential transformer are used???
Ans: dry type PTs are used

(6)for high voltages (more than 3.3kv) which potential transformer is used????
Ans:oil immersed PTs are used

### Questions On The Tap Changing Of Electrical Transformers

(1)when we can done tap changing in transformer???
Ans:The tap-changing may be done when the transformers are disconnected from the circuit or when operating on load.

(2)how manny type will be there for tap changing in transformer???
Ans:There are two types of Tap-changers:
(i) OFF-circuit Tap Changer
(ii) ON-load Tap Changer (OLTC)

(3)which type of tap changing is made by ON- load tap changer (OLTC). ??
Ans:The daily or short time voltage adjustments .

(4)give the reason The tapping are provided on the high voltage(h. v.) winding?????
Ans:reason is give as below:
(i) The number of turns in High Voltage winding (h.v.) is large and therefore a fine voltage regulation can be obtained.
(ii) The current on the h.v. side is small.
(iii) The Lv. winding is placed on the inside nearer to the core while hv winding is placed on the outside.

(5)practical considerations tap changer is proferred to provide on which winding.??
Ans: high voltage

Read The Theory Concept On The Tap Changing Of The Electrical Transformers :https://www.theengineeringstreet.com/2018/03/tap-changing-in-electrical-transformer.html

### Questions On The  Parallel Operations Of Three Phase Transformers

(1)when The transformers are said to be connected in parallel????
Ans: when the primaries of two or more trannformers are connected to a common source or supply and the secondaries are connected to supply a common load.

(2)Necessity of parallel operation of transformers???
Ans:(i) to supply the load in excess of the rating of an e existing transformer, an additional transformer can be connected in parallel

(ii) when one transformer in taken out of service for maintenance or repair, the other transformer maintains the continuity of supply to the consumers

(iii) if any one transformer fails to operate, there is no interruption of the power supply

(iv) to increase the relinbility of the power syetem

(3)give essential condition of connection of transformer in parallel???
Ans:(i) Same polarity
(ii) same voltage ratio
(iii) same phase sequence
(iv) Zero relative phase displacement

(4), give the desirabal conditions to be satisfied for better load sharing and operating power factor in parallel connection of transformer????
Ans:
(i) Equal per unit impedances and

(ii) Equal ratios of resistance to reactance(R/X)

Read The Theory Concept Of The Parallel Operation Of Three Phase Transformers https://www.theengineeringstreet.com/2018/03/parallel-operation-of-transformer.html

### Questions On The Types Of Connection Of Three Phase Transformers Connection

(1)Which is the most economical connection for small, high voltage transformers. ???
Ans:star/star

(2) Which connection have Possibility to provide neutral connection. ??
Ans:star/star

(3) Which connection is more suitable for large, low voltage transformers.??
Ans:Delta/Delta

(4)which connection is satisfactory performance even if there is large unbalanced in load. ??
Ans:Delta/Delta

(5)what is disadvantage of Delta/Delta connection of transformer??
Ans:The absence of star or neutral point

(6)The third harmonic voltages are absent from the line voltage in which connection???
Ans:star/star and delta/delta

(7)Which connection is most commonly used for power supply transformers ???
Ans:star/delta or delta/star

(8)what is advantage of star/delta or delta/star connection??
Ans:The neutral point allows

(9)Which connection reduces the third harmonic voltages ??
Ans:Zig-Zag connection

(10) For a given total voltage per phase, the Zig Zag side requires how many turns as compared to normal phase connection. ??
Ans:15% more

Read The Theory Concept Of The Types Of Connection Of Three Phase Transformers https://www.theengineeringstreet.com/2018/03/connection-of-three-phase-transformer.html

Challenging Example For Electrical Engineer

Ex :  A Transformer Have 500 turnes Of Primary Winding  And 10 Turnes Of Secondary Winding Than Determine The Secondary Voltage If The Secondary Circuit is Open And A Primary Voltage Is 120V.??

Hint  : --- k = N2/N1
:---- k= U2/U1