Electrical Machines Test Questions - Set 13

1)   The stator of split phase induction motor has two windings, main winding and auxiliary winding. These windings are displaced in space by

a. 30 electrical degrees
b. 90 electrical degrees
c. 120 electrical degrees
d. 180 electrical degrees
Answer  Explanation 

ANSWER: 90 electrical degrees

Explanation:
No explanation is available for this question!


2)   The flux under the unshaded pole of shaded pole induction motor

a. Is in equal phase of flux under the shaded pole
b. Lags the flux under the shaded pole
c. Leads the flux under the shaded pole
d. None of these
Answer  Explanation 

ANSWER: Leads the flux under the shaded pole

Explanation:
No explanation is available for this question!


3)   A two phase servomotor is commonly used in feedback control system to drive the loads and as sensors to measure

a. Speed of controlled element
b. Position of controlled element
c. Both (a) and (b)
d. None of these
Answer  Explanation 

ANSWER: Both (a) and (b)

Explanation:
No explanation is available for this question!


4)   For moment of inertia to be small in two phase servomotor, the ratio of rotor diameter to its length should be

a. Equal to 1
b. small
c. large
d. All of these
Answer  Explanation 

ANSWER: small

Explanation:
No explanation is available for this question!


5)   A load of 110kW at 0.8 power factor is to be shared by two single phase transformer with equal turns have impedances equal to (0.4 + j 0.2) and (0.6 + j 0.8) with respect to secondary. How will they share the load if they are operating in parallel?

a. 80kW, 30kW
b. 82.55kW, 28.45kW
c. 75.55kW, 24.45kW
d. 85.45kW, 24.55kW
Answer  Explanation 

ANSWER: 85.45kW, 24.55kW

Explanation:
No explanation is available for this question!


6)   If two transformers are operated in parallel with voltage ratio of transformer 1 slightly greater than that of 2. E1 and E2 are the induced emf of transformer 1 and 2, and Z1 and Z2 are the impedances then the circulating current is given by

a. (E1-E2) / (Z1+Z2)
b. (E1+E2) / (Z1+Z2)
c. (Z1-Z2) / (E1-E2)
d. (Z1-Z2) / (E1+E2)
Answer  Explanation 

ANSWER: (E1-E2) / (Z1+Z2)

Explanation:
No explanation is available for this question!


7)   For the same excitation voltage and winding currents, the autotransformer gives

a. Less output than two winding transformer
b. Equal to the output of two winding transformer
c. Half of the output of two winding transformer
d. More than the output of the two winding transformer
Answer  Explanation 

ANSWER: More than the output of the two winding transformer

Explanation:
No explanation is available for this question!


8)   In a step down autotransformer, if the transformation ratio increases then the saving of copper

a. Increases
b. Decreases
c. Remains same
d. None of these
Answer  Explanation 

ANSWER: Increases

Explanation:
No explanation is available for this question!


9)   If the transformation ratio of an autotransformer is given by V2 / V1 then the ratio of power transferred to that of input power is given by

a. (V2-V1) / V1
b. (V2+V1) / V1
c. (V1-V2) / V1
d. V2 / V1
Answer  Explanation 

ANSWER: V2 / V1

Explanation:
No explanation is available for this question!


10)   Use of an autotransformer is economical when its transformation ratio is

a. Near unity
b. Much greater than unity
c. Much lesser than unity
d. None of these
Answer  Explanation 

ANSWER: Near unity

Explanation:
No explanation is available for this question!


11)   If an autotransformer having transformation ratio equal to 0.6 is supplying a load of 8kw then its power transferred from primary to secondary is given by

a. 3 kW
b. 3.2 kW
c. 3.4 kW
d. 3.5 kW
Answer  Explanation 

ANSWER: 3.2 kW

Explanation:
No explanation is available for this question!


12)   In an autotransformer if the power transferred inductively is equal to the power conducted through, then transformation ratio is given by

a. 1
b. 0.5
c. 2
d. 0
Answer  Explanation 

ANSWER: 0.5

Explanation:
No explanation is available for this question!


13)   Whether the given autotransformer is step up or step down, its VA rating is always

a. Greater than the two winding transformer
b. Equal to the two winding transformer
c. lesser than the two winding transformer
d. cannot say
Answer  Explanation 

ANSWER: Greater than the two winding transformer

Explanation:
No explanation is available for this question!


14)   Compared to the two winding transformer, in an autotransformer the leakage reactance and copper losses is

a. less, more
b. less, less
c. more, more
d. more, less
Answer  Explanation 

ANSWER: less, less

Explanation:
No explanation is available for this question!


15)   If a two winding transformer is converted into an autotransformer by applying additive polarity and subtractive polarity which results in the secondary voltages of 1840 and 1810 volts. Then the primary and secondary voltages of transformer are

a. 1800V, 50V
b. 1810V, 40V
c. 1820V, 30V
d. 1825V, 15V
Answer  Explanation 

ANSWER: 1825V, 15V

Explanation:
No explanation is available for this question!


16)   A star connected three phase transformer is provided with tertiary delta connected winding which allows the flow of

a. Second harmonic of exciting current
b. Third harmonic of exciting current
c. Fifth harmonic of exciting current
d. Seventh harmonic of exciting current
Answer  Explanation 

ANSWER: Third harmonic of exciting current

Explanation:
No explanation is available for this question!


17)   A ferro resonant transformer regulation is also known as

a. Constant current transformer
b. Constant voltage transformer
c. Variable current transformer
d. Variable voltage transformer
Answer  Explanation 

ANSWER: Constant current transformer

Explanation:
No explanation is available for this question!


18)   In a constant voltage transformer, the primary winding and secondary winding is formed by the

a. capacitor, linear inductor
b. Non linear inductor, capacitor
c. Linear inductor and non linear inductor
d. Capacitor, non linear inductor
Answer  Explanation 

ANSWER: Linear inductor and non linear inductor

Explanation:
No explanation is available for this question!


19)   A constant voltage transformer is fed with the sinusoidal input voltage. Its output is

a. Sinusoidal
b. Flat topped
c. Saw tooth
d. Zig-zag
Answer  Explanation 

ANSWER: Flat topped

Explanation:
No explanation is available for this question!


20)   The output voltage of constant voltage transformer contains excessive harmonics which can be filtered out by using

a. RC filter
b. RL filter
c. LC filter
d. None of these
Answer  Explanation 

ANSWER: LC filter

Explanation:
No explanation is available for this question!


21)   The constant voltage transformers are most commonly used in

a. Personal computers
b. Arc welding
c. Power distribution
d. Electric cars
Answer  Explanation 

ANSWER: Personal computers

Explanation:
No explanation is available for this question!


22)   In the operation of constant current transformer, two magnetic fields are produced. The magnetic field produced in the secondary is

a. In the same direction of magnetic field produced in the primary
b. In the opposite direction of magnetic field produced in the primary
c. Perpendicular to the direction of magnetic field produced in the primary
d. Both (b) and (c)
Answer  Explanation 

ANSWER: In the opposite direction of magnetic field produced in the primary

Explanation:
No explanation is available for this question!


23)   The constant current transformer are mainly used for

a. Supplying series connected street light
b. Personal computers
c. Arc welding
d. Electric toys
Answer  Explanation 

ANSWER: Supplying series connected street light

Explanation:
No explanation is available for this question!


24)   The high leakage impedance transformers are suitable for the applications of

a. Arc welding
b. Personal computers
c. Street lights
d. Electric lamp
Answer  Explanation 

ANSWER: Arc welding

Explanation:
No explanation is available for this question!


25)   Small iron core transformers used in certain frequency range is also called audio frequency transformer. The audio frequency range is

a. 20 t0 2000 Hz
b. 20 to 20000 Hz
c. 2 to 2000 Hz
d. 200 to 20000 Hz
Answer  Explanation 

ANSWER: 20 to 20000 Hz

Explanation:
No explanation is available for this question!


26)   Pulse transformers are small in size. The leakage inductance and permeability of alloy used is

a. Low, high
b. Low, low
c. High, low
d. High, high
Answer  Explanation 

ANSWER: Low, high

Explanation:
No explanation is available for this question!


27)   In a three phase transformer, the angle between two consecutive cores is

a. 30 degree
b. 60 degree
c. 120 degree
d. 150 degree
Answer  Explanation 

ANSWER: 120 degree

Explanation:
No explanation is available for this question!


28)   In a three phase transformer, the current flowing in three primaries produces three corresponding fluxes. The sum of these three fluxes at any instant is

a. Zero
b. Three times of any individual flux
c. One third of any individual flux
d. None of these
Answer  Explanation 

ANSWER: Zero

Explanation:
No explanation is available for this question!


29)   A bank of three single phase transformer can be used for obtaining the three phase output. Three magnetic circuits produced in case of a bank of three single phase transformer and in case of single phase transformer are

a. Linked, independent
b. Independent, linked
c. Linked, linked
d. Both are independent
Answer  Explanation 

ANSWER: Independent, linked

Explanation:
No explanation is available for this question!


30)   For the star - star connection of three phase transformer, the phase angle between the phase voltages and line voltages on both primary and secondary side is

a. 0 degree
b. 30 degree
c. 60 degree
d. 120 degree
Answer  Explanation 

ANSWER: 30 degree

Explanation:
No explanation is available for this question!