ONLINE Multiple Choice Questions EE-Synchronous Motors PART 9


121. In a synchronous motor, under running
conditions, the angle between the induced voltage and supply voltage will be
(A) zero
(B) between 0 and 90°
(C) between 90° and 180°
(D) more than 180°.

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122. The rotor of a synchronous motor can only
run at synchronous speed of the stator magnetic field due to
(A) Faraday’s law of electro-magnetic
induction
(B) Lenz’s law
(C) Magnetization of rotor poles by stator
magnetic field
(D) Interlocking action between stator and
rotor fields.

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123. An inverted V-curve of a synchronous
motor is the variation of
(A) field current and power factor at
constant load
(B) supply voltage and field current at
constant excitation
(C) power factor and supply voltage during
hunting
(D) supply voltage and excitation current at
constant load.

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124. Damper windings are provided on
(A) pole faces
(B) separate armature
(C) rotor shaft
(D) stator frame.

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125. Hunting of a synchronous motor may be due
to
(A) pulsations in power supply
(B) reciprocating type of load
(C) pulsating torque of driven equipment
(D) any of the above.

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126. The V-curves of a synchronous motor show
relationship between
(A)
armature current and supply voltage
(B) dc field current and ac armature
current
(C) excitation current and back emf
(D) none of the above.

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127. In a synchronous motor with field under
excited, the power factor will be
(A)
leading
(B) lagging
(C) unity
(D)
none of the above.

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128. In a synchronous motor, maximum value of
torque angle is
(A)
Below 45 degrees electrical
(B)
45 degrees electrical
(C) 90 degrees electrical
(D) Above 90 degrees electrical.

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129. In a synchronous motor, net armature
voltage is of Eb and V
(A) Vector sum
(B) Vector difference
(C) Arithmetic difference
(D) Arithmetic sum.

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130. Increasing load on a
normally-excited synchronous motor, the power factor
(A) remain unchanged
(B) becomes increasing lagging
(C) becomes increasing leading
(D) none of the above.

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131. Synchronous motor speed is controlled by
varying
(A) supply voltage
only
(B) supply frequency only
(C) supply voltage and frequency both
(D) none of the above.

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132. Maximum electrical power input of a
synchronous motor is
(A) (Vt Ef) / Xs
(B)
V2t / Xs
(C) E2f/ Xs
(D) Xs/ (Vt Ef )
where the symbols have their usual meanings.

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133. In a synchronous motor armature reaction
at rated voltage and zero power factor leading is
(A) Demagnetizing
(B) Cross magnetizing
(D) Magnetizing
(D)
None of the above.

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134. A synchronous motor is operating with
excitation adjusted for unity power factor current at constant load. On
increasing the excitation, the power factor
(A) will lag
(B) will lead
(C) will become zero
(D) none of the above.

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135. A synchronous motor is operated from a
bus voltage of 1.0 pu at 1.0 pu pf leading current. The synchronous reactance
is 0.5 p.u. The excitation e.m.f of the motor is
(A) 0.5
(B)
1
(C) 1.5
(D)
3.

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136. A 3-phase synchronous motor connected to
an infinite bus is operating at half full-load with normal excitation. When the
load on the synchronous motor is suddenly increased
(A) its speed will first decrease and then
become synchronous
(B) its speed will first increase and then
become synchronous
(C)
its
speed will fluctuate around synchronous speed and then become synchronous
(D) its speed will remain unchanged.

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137. A synchronous motor operating at rated
voltage draws 1.0 pu current at 1.0 power factor. The machine parameters are :
synchronous reactance 1.0 pu ; armature resistance, negligible. Apart from
supplying this rated power, if the motor has to supply an additions! leading
reactive power of 0.8 pu, then the field current has to be increased by
(A) 42%
(B)
46%
(C) 52%
(D)
60%.

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ONLINE Multiple Choice Questions EE-Synchronous Motors PART 10
ONLINE Multiple Choice Questions EE-Synchronous Motors PART 8

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