Electrical Questions
Question Bank - 2
40 - Questions
1) what is a need of commutator??
15)how many type for exciting to magnetic system??
Ans: two type (1) single excited and (2) doubly excited
16)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
17)Give the formula For angular movements of armature the electromagnetic torque for a linear system ???
T=(1/2)*(i^2)*(dL/d§)
Where §=angle
18)What is doubly excited magnetic system??
Ans:A magnetic system which is excited by two independent source is called doubly excited magnetic circuit.
Where §=anglr
Ir= rotor current
Is= stator current
24)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
25) 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
26)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
27)Magnetic losses is also known as????
Ans:These losses are also called iron loss or core loss.
28)magnetic loss consist which losses???
Ans:
Iron losse consists of
(1) Hysterisis losses and
(2) Eddy current losse.
And Second One Copper Losses
29)magnetic loss are about _____of full load losses.???
Ans: 20% to 30%
30)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.
31)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
32)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.
33)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.
34) give thr Function of starter ???
Ans:The device which is used to start the d.c. motor is called a starter.
The function of the starter is to limit the starting high current to a safe value.
35)When the motor is at reast the speed of the motor is zero hence back emf Eb will be ________????
Ans: zero
36)The starting current may be _______ that of full load current. ??
Ans:5 to 7 times
37)The dc shunt and compound motor is started by the how many types af starters and which?????
Ans : Two
(1)Three pointt starter and
(2)Four paint starter
38) The starter is used only for the short duration ______ time which limits the starting high current to a safe value.???
Ans:the short duration (5 to 10 sec)
39)when the armature of a dc motor rotates, in a magnetic field, its conductors cut the magnetic flux Therefore an emf is induced in them according to _______law?????
Ans:Faraday's laws of Electromagnetic induction,
Ans: the current induced in armature conductors of a d.c. generator are alternating. To make their flow unidirectional in the external circuit, we need a commutator.
2) what is full form of M.N.A.???
Ans:magnetic neutral axis
3) list the ways of improving commutation.???
Ans:
(1) resistance commutation and
(2) e.m.f. commutation( which is done with the help of either brush lead or interpoles, usually the later).
4)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.
5)what is the full form of G. N. A???
Ans: geometrical neutralaxis or plane(G.N.A.)
6)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.
7)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.
8)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.
9) define function of d.c. motor???
Ans: An electric motor is a machine which converts electric energy into mechanical energy.
10) In d.c. motor conductor is experienced force by whose principle??
Ans: Fleming's Left-hand Rule
11)what is the function kf 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.
12) In lathes machine which type of motor are uses???
Ans:shunt type d.c. motor
13)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
14)For intermittent high torque loads which motor are used??
Ans: Comulative compound type d.c. motor
2) what is full form of M.N.A.???
Ans:magnetic neutral axis
3) list the ways of improving commutation.???
Ans:
(1) resistance commutation and
(2) e.m.f. commutation( which is done with the help of either brush lead or interpoles, usually the later).
4)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.
Ans: geometrical neutralaxis or plane(G.N.A.)
6)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.
7)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.
8)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.
9) define function of d.c. motor???
Ans: An electric motor is a machine which converts electric energy into mechanical energy.
10) In d.c. motor conductor is experienced force by whose principle??
Ans: Fleming's Left-hand Rule
11)what is the function kf 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.
12) In lathes machine which type of motor are uses???
Ans:shunt type d.c. motor
13)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
14)For intermittent high torque loads which motor are used??
Ans: Comulative compound type d.c. motor
15)how many type for exciting to magnetic system??
Ans: two type (1) single excited and (2) doubly excited
16)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
17)Give the formula For angular movements of armature the electromagnetic torque for a linear system ???
T=(1/2)*(i^2)*(dL/d§)
Where §=angle
18)What is doubly excited magnetic system??
Ans:A magnetic system which is excited by two independent source is called doubly excited magnetic circuit.
19)Give the example of doubly excited magnetic system??
Ans:The synchronous machines and d.c. machines .
20)Give formula for satisfied the energy conversion principle in doubly excited magnetic system??
Ans: dWe = dWm + dWf
21)Give the formula of Magnetic torque developed in doubly excited magmetic system??
Ans:Tm d§ =(1/2)(i^2) dLs + (1/2)(ir^2) dLr +(is) (ir) dMWhere §=anglr
Ir= rotor current
Is= stator current
22)The voltage build-up in a self-excited dc generator depends up on _________????
Ans: the presence of a residual flux in the field poles.
23) When the generator is started a small emf is induced due to _______???
Ans: residual magnetism
24)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
25) 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
26)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
27)Magnetic losses is also known as????
Ans:These losses are also called iron loss or core loss.
28)magnetic loss consist which losses???
Ans:
Iron losse consists of
(1) Hysterisis losses and
(2) Eddy current losse.
And Second One Copper Losses
29)magnetic loss are about _____of full load losses.???
Ans: 20% to 30%
30)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.
31)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
32)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.
33)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.
34) give thr Function of starter ???
Ans:The device which is used to start the d.c. motor is called a starter.
The function of the starter is to limit the starting high current to a safe value.
35)When the motor is at reast the speed of the motor is zero hence back emf Eb will be ________????
Ans: zero
36)The starting current may be _______ that of full load current. ??
Ans:5 to 7 times
37)The dc shunt and compound motor is started by the how many types af starters and which?????
Ans : Two
(1)Three pointt starter and
(2)Four paint starter
38) The starter is used only for the short duration ______ time which limits the starting high current to a safe value.???
Ans:the short duration (5 to 10 sec)
39)when the armature of a dc motor rotates, in a magnetic field, its conductors cut the magnetic flux Therefore an emf is induced in them according to _______law?????
Ans:Faraday's laws of Electromagnetic induction,
40)what is the job of back emf in dc generator???
Ans:In dc generators, the opposition is provided by magnetic force and in dc motors, back e m f does this job.
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