Transformer objective question with answer 11 to 40

Transformer objective question with answer  11 to 40

Q no 11. Gas is usuallynot liberated due to dissociation of transformer oil unless the oil temperature                exceeds

              a ) 50℃
              b ) 80℃
              c ) 100 ℃
              d ) 150 ℃

explanation

                  answer : d ) 150 ℃

Q no 12. Which of the following properties is not necessarily desirable for material for transformer core ?

               a ) low hysteresis loss

               b ) high permeability

               c ) high thermal conductivity

               d ) adequate mechanical strength

explanation

                  answer : c ) high thermal conductivity

Q no 13 .The leakage flux in a transformer depends upon

              a ) load current

              b ) load current and voltage

              c ) load current , voltage and frequency

              d ) load current , voltage , frequency and power factor

explanation

                  answer :  a ) load current

Q no 14 . Noise level test in a transformer is a

               a ) special test

               b ) routine test

               c ) type test

               d ) none of the above

explanation

                  answer : c ) type test

Q no 15 . The core used in high frequency transformer is usually 

                a ) copper core

                b ) cost iron core

                c ) air core

                d ) mild steel core

explanation

                  answer  c ) air core

Q no 16 . silicon steel used in laminations mainly reduces

                a ) hysteresis loss

                b ) eddy current losses

                c ) copper losses

                d ) all of the above

explanation

                  answer  a ) hysteresis loss

Q no 17. During short - circuit test iron losses are negligible because 

              a ) the current on secondary side is negligible

              b ) the voltage on secondary side does not vary

              c ) the voltage applied on primary side is low 

              d ) full - load current is not supplied to the transformer

explanation

                  answer   c ) the voltage applied on primary side is low 

Q no 18 Two transformers are connected in parallel . these transformers do not have equal percentage                             impedance . this is likely to result in

              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 proportional to their KVA rating

explanation

                  answer  d ) loading of the transformers not in proportional to their KVA rating

Q no 19 . The changes in volume of transformer  cooling oil due to variation of atomspheric temperature during                   day and night is taken care of by which part of transformer

              a ) conservator

              b ) breather

              c ) bushing

              d ) buchholz relay

explanation

                  answer a ) conservator

Q no 20 When a given transformer is run at rated voltage but reduced frequency , its
               a ) flux density remains unaffected
               b ) iron losses are reduced
               c ) core flux density is reduced
               d ) core flux density is increased

explanation

                  answer   d ) core flux density is increased

Q no 21. In an actual transformer the iron loss remains practically constant from no load to full load because
A ) value of transformation ratio remain constant
B ) permeability of transformer core remains constant
C ) core flux remains practically constant
D ) primary voltage remains constant
E ) secondary voltage remains constant

Q no 22. Negative voltage regulations is indicative that the load is
A ) capacitive only
B ) inductive only
C ) inductive or resistive
D ) none of the above

Q no 23. Iron loss of a transformer can be measured by
A ) low power factor wattmeter
B ) unity power factor wattmeter
C ) frequency meter
D ) any type of wattmeter

Q no 24. Natural air cooling is generally restricted for transformer up to
A ) 1.5 MVA
B ) 5 MVA
C ) 15 MVA
D ) 50 MVA

Q no 25. A shell type transformer has
A ) high eddy current losses
B ) reduced magnetic leakage
C ) negligible hysteresis losses
D ) none of the above

Q no 26. A transformer can have regulation closer to zero
A ) on full - load
B ) on overload
C ) on leading power factor
D ) on zero power factor

Q no 27.  For given applied voltage , with the increase in frequency  of the applied voltage
A ) eddy current loss will decrease
B ) eddy current loss will increase
C ) eddy current loss will remains unchanged
D ) none of the above

Q no 28. For a transformer , operating at constant load current , maximum efficiency will occur at
A ) 0.8 leading power factor
B ) 0.8 lagging power factor
C ) zero power factor
D ) unity power factor

Q no 29. The efficiency of a transformer , under heavy loads , is comparatively low because
A ) copper loss becomes high in proportional to the output
B ) iron loss is increased considerably
C ) voltage drop both in primary and secondary becomes large
D ) secondary output is much less as compared to primary input

Q no 30. Minimum voltage regulation occurs when the power factor of the load is
A ) unity
B ) lagging
C ) leading
D ) zero

Q no 31. The efficiencies of transformer compared with that of electric motor of the same power are
A ) about the same
B ) much smaller
C ) much higher
D ) somewhat smaller
E ) none of the above

Q no 32. In an ideal transformer , on no load the primary voltage is balanced by
A ) the primary induced emf
B ) the secondary induced emf
C ) the secondary voltage
D ) the drop across resistance and reactance

Q no 33. As per the Name plate of a transformer , the secondary normal voltage is 220 V . Which of the following statement about it is correct ?
A ) 220 V is the no load voltage
B ) the no load voltage is more than 220 V
C ) the secondary voltage increase with increasing load
D ) at a load which draws the rated current the voltage become less than 220V

Q no 34. A transformer having a turn ratio 1 : 5 and a resistance of 1000 ohms is connected across the secondary terminal , the resistance offered to a current flowing in the primary will be
A ) 10 ohms
B ) 20 ohms
C ) 40 ohms
D ) 60 ohms

Q no 35. Which of the following statement about a transformer having a small short circuit voltage is true ?
A ) a low short circuit current flows through the transformer
B ) a high short circuit current flows through the transformer
C ) the transformer has high copper losses during the operation
D ) the transformer has high iron losses during the operation
E ) the transformer has a small transformation ratio

Q no 36. If a transformer core is made of copper and coils are made up of steel wire , then
A ) eddy current losses will be less
B ) copper losses in the winding will be more
C ) magnetising current will be reduced
D ) all of the above

Q no 37. The dielectric strength of transformer oil is expected to be
A ) 1 kV
B ) 33 kV
C ) 100 kV
D ) 330 kV

Q no 38. A common method of cooling a power transformer
A ) natural air cooling
B ) air blast cooling
C ) oil cooling
D ) any of the above

Q no 39. In a transformer the function of a conservator is to
A ) provide fresh air for cooling the transformer
B ) supply cooling oil to transformer in time of need
C ) protect the transformer from damage when oil expends due to heating
D ) none of the above

Q no 40. Spacers are provided between adjacent coils
A ) to provide free passage to the cooling oil
B ) to insulate the coils from each other
C ) both A and B
D ) none of the above