Skip to main content

Power Electronics Part- 5 Objective Questions with Answers

Power Electronics Objective Questions with Answers: Part-5

1. SCR is the solid state equivalent of
(a) Transistor
(b) Thyratron
(c) Vacuum diode
(d) Crystal diode

Answer: B
2. With gate open, if the supply voltage exceeds the breakover voltage of SCR, then SCR will conduct
(a) False
(b) True
(c) For DC
(d) For AC

Answer: B
3. The SCR is turned off when the anode current falls below
(a) Forward current rating
(b) Break over voltage
(c) Holding current
(d) Latching current

Answer: C
4. In a SCR circuit, the angle of conduction can be changed by changing
(a) Anode voltage
(b) Anode current
(c) Forward current rating
(d) Gate current

Answer: D
5. The normal way to close a SCR is by appropriate
(a) Gate current
(b) Cathode current
(c) Anode current
(d) Forward current

Answer: A
6. An SCR has ......PN junctions
(a) Two
(b) Four
(c) Three
(d) One

Answer: C
7. If gate current is increased, the anode-cathode voltage at which SCR closes is.....
(a) Increased
(b) Decreased
(c) Maximum
(d) Least

Answer: B
8. A conducting SCR can be opened by reducing ..... to zero
(a) Supply voltage
(b) Grid voltage
(c) Grid current
(d) Anode current

Answer: A
9. With gate open, a SCR can be turned-on by making supply voltage....
(a) Minimum
(b).Reverse
(c) Equal to cathode voltage
(d) Equal to breakover voltage

Answer: D
10. If firing angle in a SCR rectifier is increased, output is....
(a) Increased
(b) Maximum
(c) Decreased
(d) Unaffected

Answer: C
11. A SCR is a ...switch
(a) Two directional
(b) Unidirectional
(c) Three directional
(d) Four directional

Answer: B
12. The anode of SCR is always maintained at........potential with respect to cathode
(a) Positive
(b) Zero
(c) negative
(d) Equipotential

Answer: A
13. IF the chopper switching frequency is 200Hz and Ton time is 2ms, the duty cycle is
(a) 0.4
(b) 0.8
(c) 0.6
(d) None of the above

Answer: A
14. Speed control of induction motor can be effected by varying
(a) Flux
(b) Voltage input to stator
(c) Keeping rotor coil open
(d) None of the above

Answer: B
15. In a Dc motor if the field coil gets opened, the speed of the motor will
(a) Decrease
(b) Come to stop
(c) Increase
(d) None of the above

Answer: C

 Solution Hint:
[11] SCR will conduct in one direction only. So it act as a unidirectional switch.
[13] T=1/f, D = TON/T
Labels:

Comments

Post a Comment

Comment Policy
We’re eager to see your comment. However, Please Keep in mind that all comments are moderated manually by our human reviewers according to our comment policy, and all the links are nofollow. Using Keywords in the name field area is forbidden. Let’s enjoy a personal and evocative conversation.

Popular posts from this blog

Practical Commutation

The e.m.f. induced in each coil of armature is alternating in nature. If load is connected, the current flowing will also be alternating. But the flow of current in a d.c. generator must be undirectional. This can be achieved by the use of commutator. When the armature conductors are under the influence of one pole they carry current in one direction whereas the current is reversed when the conductors are under the influence of other pole. This reversal of current takes place along the magnetic neutral axis. Fig. 1 Note : The reversal of current is likely to take place in short interval when a coil is short circuited by a brush so that transfer of current from one direction to other is carried out without any sparking. This process is called commutation.        Thus a process by which current in the short circuited coil is reversed while it crosses the MNA is called commutation. The time during which the coil remains short circuited is known as...
1 comment
Read more

Demagnetising and Cross Magnetizing Conductors

The conductors which are responsible for producing demagnetizing and distortion effects are shown in the Fig.1. Fig. 1        The brushes are lying along the new position of MNA which is at angle θ  from GNA. The conductors in the region AOC = BOD = 2θ  at the top and bottom of the armature are carrying current in such a direction as to send the flux in armature from right to left. Thus these conductors are in direct opposition to main field and called demagnetizing armature conductors.         The remaining armature conductors which are lying in the region AOD and BOC carry current in such a direction as to send the flux pointing vertically downwards i.e. at right angles to the main field flux. Hence these conductors are called cross magnetizing armature conductors which will cause distortion in main field flux.        These conductors are shown in the Fig. 2 Fig. 2  ...
Post a Comment
Read more

Winding Pitches

Now we will consider the definitions of different types of winding pitches, required in the design of the armature winding. 1.1 Back Pitch         The distance which is measured interns of armature conductors i.e. between top and bottom coil sides of a coil measured around the back of the armature i.e. away from the commutator is called back pitch and is denoted by . It is measured interms of coil sides. Note : Since it is difference between odd and even number, it is always odd number.        The size of the coil is decided by the back pitch. The back pitch is normally equal to coilsides per pole. It is shown for lap and wave type of winding in the Fig. 1. Fig. 1        The back pitch for the winding shown in the Fig. 1 is y b = 14 - 1 = 13 as coilsides 1and 14 are of coil number 1. 1.2 Front Pitch        It is defined as the distance measured between two c...
Post a Comment
Read more