Saturday, August 17, 2013

Transformers Objective Questions: Part-9

Transformers Objective Questions with Answers:

[1] High frequency transformers sometimes make use of ferrite cores because it has
A. High specific gravity
B. High resistance
C. High hysteresis
D. low permeability


[2] Harmonics in transformer result in
A. Increased core losses
B. Increased I2R losses
C. Magnetic interference with communication circuits
D. All of the above


[3] The full load copper loss of a transformer is 1600W. At half-load the copper loss will be
A. 6400W
B. 1600W
C. 800W
D. 400W


[4] Power transformers are generally designed to have maximum efficiency around
A. No load
B. Half load
C. Near full load
D. 10% overload


[5] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results
A. Short-circuiting of the secondaries
B. Power factor of one of the transformers is leading while that of the other lagging
C. Transformers having higher copper losses will have negligible core losses
D. Loading of the transformers not in proportion to their kVA ratings.


[6] The changes in volume of transformer cooling oil due to variation o
f atmospeheric temperature during day and night is taken care of by which part of transformer?
A. Conservator
B. Breather
C. Bushings
D. Buchholz relay


[7] The transforme
r laminations are insulated from each other by
A. Mica strip
B. Thin coat of varnish
C. Paper
D. Any of the above


[8] Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type


[9] During open circuit test of a transformer
A. Primary is supplied rated voltage
B. Primary is supplied full load current
C. Primary is supplied current at reduced voltage
D. Primary is supplied rated kVA


[10] Which of the following is not standard voltage for power supply i
n India
A. 11kV
B. 33kV
C. 66 kV
D. 122 kV


[11] The low voltage winding of a 400/230 volt, 1-phase, 50Hz transformer is to be connected to a 25Hz supply in order to keep the magnetization current at the same level as that for normal 50Hz supply at 25Hz the voltage should be [Gate 1997]
a) 230V
b) 460V
c) 115V
d) 65V
Answer: C


[12] The primary current in the current transformer is dictated by [Gate 1997]
a) The secondary burden
b) The core of the transformer
c) The load current
d) None of the above
Answer: A

10:26 PM

15 comments:

  1. In ferrite core T/ f in use for to reduce iron losses
    but answer given reduce resistance how ?
    Plz. Clear

    ReplyDelete
  2. In ferrite core T/ f in use for to reduce iron losses
    but answer given reduce resistance how ?
    Plz. Clear

    ReplyDelete
    Replies
    1. ferrite core t/f already have high resistence and no need of laminations like silicon steel core t/f .due to high ferrite resistence decrease the eddy current losses.

      Delete
    2. Ferrite core have high resistence

      Delete
    3. Ferrite core has high resistivity .so it has high resistance which results in the reduction of eddy current. So eddy current losses can be reduced which is predominant at high frequencies. That is why ferrite cores are used in high frequency transformer.

      Delete
  3. thank u .
    can u provide answers with justifications

    ReplyDelete
  4. very usefull information thanks

    ReplyDelete