MCQOPTIONS
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MCQOPTIONS
This section includes 517 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
Let α be the angle, in electrical degrees, by which the span of the coil is less than a pole pitch in alternator. At the fundamental frequency, the pitch factor is equal to: |
| A. | cos α |
| B. | \(cos\frac{\alpha }{2}\) |
| C. | sin α |
| D. | \(sin\frac{\alpha }{2}\) |
| Answer» C. sin α | |
| 102. |
In alternators, salient pole type rotors are generally used with prime movers of |
| A. | Low speed |
| B. | Medium speed |
| C. | High speed |
| D. | Any speed |
| Answer» B. Medium speed | |
| 103. |
A 3 phase, 8 ole, 50 Hz star connected alternator has 72 coils in 72 slots. The coils are short pitched by 3 slots. The value of the pitch factor is |
| A. | \(\frac{\sqrt{2}}{3}\) |
| B. | \(\frac{1}{2}\) |
| C. | \(\frac{\sqrt{3}}{2}\) |
| D. | 1 |
| Answer» D. 1 | |
| 104. |
A three-phase induction motor with eight poles runs from a three-phase supply of 50 Hz. What is the synchronous speed of the motor? |
| A. | 3000 rpm |
| B. | 1500 rpm |
| C. | 1000 rpm |
| D. | 750 rpm |
| Answer» E. | |
| 105. |
In a synchronous motor, |
| A. | E is always less than V |
| B. | E = V |
| C. | E is always more than V |
| D. | E may be more or less than V |
| Answer» E. | |
| 106. |
For V-curves for a synchronous motor the graph is drawn between: |
| A. | armature current and power factor |
| B. | field current and armature current |
| C. | terminal voltage and load factor |
| D. | power factor and field current |
| Answer» C. terminal voltage and load factor | |
| 107. |
Quadrature axis synchronous reactance is the ratio of ________. |
| A. | Vmin to Imax |
| B. | Vmin to Imin |
| C. | Vmax to Imax |
| D. | Vmax to Imin |
| Answer» B. Vmin to Imin | |
| 108. |
In an alternator, the nature of armature reaction at zero power factor leading loads is _______. |
| A. | cross magnetizing |
| B. | demangetizing |
| C. | non-effective |
| D. | magnetizing |
| Answer» E. | |
| 109. |
A salient-pole synchronous motor is running clockwise at no-load. If its field current is reduced to zero and then reversed, then |
| A. | the motor would stop |
| B. | the motor would run in the reverse direction |
| C. | the motor slips by one pole-pitch and continues running at synchronous speed |
| D. | the motor slips by one pole-pitch and speed would be less than synchronous speed |
| Answer» D. the motor slips by one pole-pitch and speed would be less than synchronous speed | |
| 110. |
If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from the constant voltage supply, its field excitation is increased up to normal excitation, then its power factor: |
| A. | Become more |
| B. | Become less |
| C. | All of these |
| D. | Remain constant |
| Answer» B. Become less | |
| 111. |
High speed alternators usually have ________. |
| A. | salient pole rotors |
| B. | cylindrical rotors |
| C. | both salient pole and cylindrical rotors |
| D. | None of these |
| Answer» C. both salient pole and cylindrical rotors | |
| 112. |
Calculate the distribution factor for a single layer 18 slots 2-pole three-phase stator winding |
| A. | \(3 \times \frac{{sin30^\circ }}{{sin10^\circ }}\) |
| B. | \(3 \times \frac{{sin10^\circ }}{{sin30^\circ }}\) |
| C. | \( \frac{{sin10^\circ }}{{3\;sin30^\circ }}\) |
| D. | \( \frac{{sin30^\circ }}{{3\;sin10^\circ }}\) |
| Answer» E. | |
| 113. |
In a synchronous machine, for open circuit characteristics, the final value of generated EMF Ef should be about __________ of the rated voltage. |
| A. | 50% |
| B. | 125% |
| C. | 100% |
| D. | 75% |
| Answer» C. 100% | |
| 114. |
In Potier triangle, the Potier reactance drop is 22 volts per phase at full load current of 88 amps per phase. The potier resistance per phase is |
| A. | 0.22 Ω |
| B. | 0.25 Ω |
| C. | 0.43 Ω |
| D. | 0.7 Ω |
| Answer» C. 0.43 Ω | |
| 115. |
In a stand alone synchronous generator, impact of increase in a real power load with governor valve control is |
| A. | increase in frequency |
| B. | decrease in frequency |
| C. | maintain frequency |
| D. | oscillation in frequency |
| Answer» D. oscillation in frequency | |
| 116. |
In case of an electromechanical generator, the frequency is: |
| A. | directly proportional to the voltage |
| B. | directly proportional to the speed |
| C. | indirectly proportional to the speed |
| D. | indirectly proportional to the power |
| Answer» C. indirectly proportional to the speed | |
| 117. |
An alternator has 9 slots/pole. What is the value of the pitch factor if each coil spans 8 slot pitches. |
| A. | cos 10° |
| B. | cos 45° |
| C. | cos 60° |
| D. | cos 30° |
| Answer» B. cos 45° | |
| 118. |
Potier triangle method is helpful in obtaining the voltage regulation of synchronous machines by determining the armature |
| A. | Leakage reactance and its reaction mmf |
| B. | Leakage reactance and air-gap flux |
| C. | Resistance and its reaction mmf |
| D. | Resistance and air-gap flux |
| Answer» B. Leakage reactance and air-gap flux | |
| 119. |
In alternator, the ratio \( \frac{{vector\;sum\;of\;induced\;emf\;per\;coil}}{{arhitmetic\;sum\;of\;induced\;emf\;per\;coil}} \) is known as: |
| A. | Form factor |
| B. | Power factor |
| C. | Pitch factor |
| D. | RMS value |
| Answer» D. RMS value | |
| 120. |
If the supply frequency of synchronous motor is 50 cycles/second, then the rotor must revolve at |
| A. | 25 cycles/second |
| B. | 50 cycles/second |
| C. | 100 cycles/second |
| D. | None of the above |
| Answer» C. 100 cycles/second | |
| 121. |
If the excitation and the terminal voltage of a synchronous motor are kept constant and the load is increased then _____. |
| A. | Armature current decreases and power factor becomes more leading |
| B. | Armature current increases and power factor becomes more leading |
| C. | Armature current increases and power factor becomes more lagging |
| D. | None of these |
| Answer» D. None of these | |
| 122. |
An under excited synchronous motor operates at |
| A. | lagging PF |
| B. | unity PF |
| C. | leading PF |
| D. | lagging PF at low loads and leading PF at high loads |
| Answer» B. unity PF | |
| 123. |
For zero power factor leading loads, the effect of an armature reaction in an alternator is: |
| A. | distortion |
| B. | cross-magnetizing |
| C. | magnetizing |
| D. | de-magnetizing |
| Answer» D. de-magnetizing | |
| 124. |
In slip test on a 3-phase alternator, the maximum and minimum voltage per phase are V1 and V2 respectively whereas the maximum and minimum phase currents are found to be I1 and I2 respectively. The value of the d-axis synchronous reactance xd and q-axis synchronous reactance xq are determined as |
| A. | \({x_d} = \frac{{{V_1}}}{{{I_1}}},\;{x_q} = \frac{{{V_2}}}{{{I_2}}}\) |
| B. | \({x_d} = \frac{{{V_1}}}{{{I_2}}},\;{x_q} = \frac{{{V_2}}}{{{I_1}}}\) |
| C. | \({x_d} = \frac{{{V_1}}}{{\left( {{I_{1 - }}{I_2}} \right)}},\;{x_q} = \frac{{{V_2}}}{{({I_1} + {I_2})}}\) |
| D. | \({x_d} = \frac{{({V_1} + {V_2})}}{{({I_1} - {I_2})}},\;{x_q} = \frac{{\left( {{V_1} - {V_2}} \right)}}{{\left( {{I_2} + {I_1}} \right)}}\) |
| Answer» C. \({x_d} = \frac{{{V_1}}}{{\left( {{I_{1 - }}{I_2}} \right)}},\;{x_q} = \frac{{{V_2}}}{{({I_1} + {I_2})}}\) | |
| 125. |
A three-phase synchronous motor draws 200 A from the line at unity power factor at rated load. Considering the same line voltage and load, the line current at a power factor of 0.5 leading is |
| A. | 100 A |
| B. | 200 A |
| C. | 300 A |
| D. | 400 A |
| Answer» E. | |
| 126. |
In a synchronous motor if the back emf is approximately equal to the applied voltage, then |
| A. | The torque generated is maximum |
| B. | The excitation is said to be hundred percent |
| C. | The excitation is said to be zero percent |
| D. | The motor is said to be fully loaded |
| Answer» C. The excitation is said to be zero percent | |
| 127. |
Maximum speed of a synchronous machine for 50 Hz is |
| A. | 1500 rpm |
| B. | 3000 rpm |
| C. | 20000 rpm |
| D. | 30000 rpm |
| Answer» C. 20000 rpm | |
| 128. |
For which of the following reasons are lamps bright synchronization preferred to lamps dark? |
| A. | Flickering is pronounced |
| B. | Brightness can be seen easily |
| C. | Sharper and more accurate synchronization |
| D. | It can be performed quickly |
| Answer» D. It can be performed quickly | |
| 129. |
A cylindrical-rotor generator with internal voltage 2.0 pu and Xs = 1.0 pu is connected by a line reactance 0.5 pu to a round-rotor synchronous motor of synchronous reactance 1.2 pu and excitation voltage 1.35 pu. When 0.5 pu power is supplied by the generator, the electrical angular difference between the rotors would be |
| A. | 25° |
| B. | 30° |
| C. | 60° |
| D. | 120° |
| Answer» C. 60° | |
| 130. |
At lagging loads, the effect of armature reaction in an alternator is? |
| A. | Neutralizing |
| B. | Cross magnetizing |
| C. | Magnetizing |
| D. | Demagnetizing |
| Answer» E. | |
| 131. |
In synchronous motors, V-curves show relationship between: |
| A. | Armature current and supply voltage |
| B. | DC field current and AC armature current |
| C. | Excitation current and back emf |
| D. | Field current and power factor |
| Answer» C. Excitation current and back emf | |
| 132. |
A synchronous motor is operating with normal excitation. With the increase in load, the armature current drawn from the supply mains increases due to: |
| A. | Increase in resultant voltage across the armature |
| B. | Increase in power factor |
| C. | Increase in back emf |
| D. | Fall in motor speed |
| Answer» B. Increase in power factor | |
| 133. |
Calculate the highest speed at which a 60 Hz alternator can be operated. |
| A. | 3600 rpm |
| B. | 3000 rpm |
| C. | 2400 rpm |
| D. | 4200 rpm |
| Answer» B. 3000 rpm | |
| 134. |
A pilot exciter is provided on generators for which of the following reasons? |
| A. | To excite the poles of the main exciter |
| B. | To provide requisite starting torque to the generator |
| C. | To cancel the ripple frequency |
| D. | To provide requisite starting torque to the main exciter |
| Answer» B. To provide requisite starting torque to the generator | |
| 135. |
A 4-pole, wave wound armature having 45 slots with 18 conductors/slot is driven at 1200 rpm. If the flux per pole is 0.016 Wb, the generated emf will be |
| A. | 534.4 V |
| B. | 526.8 V |
| C. | 518.4 V |
| D. | 502.8 V |
| Answer» D. 502.8 V | |
| 136. |
Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:Statement (I): A synchronous motor can be used as an active device to improve the power factor of a power system.Statement (II): By over-excitation the synchronous machine would operate as a capacitor. |
| A. | Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I |
| B. | Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I |
| C. | Statement I is true but Statement II is false |
| D. | Statement I is false but Statement II is true |
| Answer» B. Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I | |
| 137. |
Identify the INCORRECT statement with regards to synchronous motors. |
| A. | It is a self-starting machine |
| B. | The field winding is placed on the rotor |
| C. | It is a constant speed motor |
| D. | The armature winding is placed on the stator |
| Answer» B. The field winding is placed on the rotor | |
| 138. |
If an alternator is operating at unity power factor, then its terminal voltage is: |
| A. | equal to the induced EMF, with zero voltage regulation |
| B. | greater than the induced EMF, with negative voltage regulation |
| C. | less than the induced EMF, with positive voltage regulation |
| D. | less than the induced EMF, with negative voltage regulation |
| Answer» D. less than the induced EMF, with negative voltage regulation | |
| 139. |
How can the reactive power delivered by a synchronous generator be controlled? |
| A. | By changing the prime mover input |
| B. | By changing the excitation |
| C. | By changing the direction of rotation |
| D. | By changing the prime mover speed |
| Answer» C. By changing the direction of rotation | |
| 140. |
Match List I (Equivalent circuit parameter) with List II (values) for a 50 MVA three phase alternator and select the correct answer. List I List IIA.Armature resistance1.1 puB.Synchronous reactance2.0.1puC.Leakage reactance3.0.01 pu |
| A. | A – 1, B – 2, C - 3 |
| B. | A – 3, B – 1, C - 2 |
| C. | A – 3, B – 2, C - 1 |
| D. | A – 1, B – 3, C - 2 |
| Answer» C. A – 3, B – 2, C - 1 | |
| 141. |
In an alternator, if α = 60°, then find the pitch factor. |
| A. | 1 |
| B. | \(\sqrt\frac{3}{4}\) |
| C. | 1/2 |
| D. | 0 |
| Answer» C. 1/2 | |
| 142. |
An integral number of slots per pole is often used in an alternator in order to: |
| A. | Eliminate harmonics in the waveform |
| B. | Provide insulation |
| C. | Permit easy installation of stator coils |
| D. | Provide easy removal in case of repair |
| Answer» B. Provide insulation | |
| 143. |
In an alternator voltage drops occur in |
| A. | armature resistance only |
| B. | armature resistance and leakage reactance |
| C. | armature resistance, leakage reactance and armature reactance |
| D. | armature resistance, leakage reactance, armature reaction and earth connections |
| Answer» D. armature resistance, leakage reactance, armature reaction and earth connections | |
| 144. |
In the Potier method of voltage regulation, which of the following characteristics is/are determined by conducting tests on the machines running at synchronous speed?(i) Open-circuit characteristic(ii) Zero power factor (lagging) characteristic(iii) Short-circuit characteristic |
| A. | (i), (ii) and (iii) |
| B. | Only (i) and (ii) |
| C. | Only (i) and (iii) |
| D. | Only (iii) |
| Answer» C. Only (i) and (iii) | |
| 145. |
In which of the following motors the Stator field and rotor rotate simultaneously |
| A. | Induction motor |
| B. | Universal motor |
| C. | D.C. motor |
| D. | Synchronous motor |
| Answer» E. | |
| 146. |
Armature reaction in an alternator primarily affect |
| A. | rotor speed |
| B. | terminal voltage per phase |
| C. | frequency of armature current |
| D. | generated voltage per phase |
| Answer» E. | |
| 147. |
Determine the pitch factor for winding: 36 stator slots, 4-poles, coil spans 1 to 8. |
| A. | cos 200 |
| B. | cos 400 |
| C. | cos 300 |
| D. | cos 800 |
| Answer» B. cos 400 | |
| 148. |
A pony motor is used for the starting of which of the following motor |
| A. | Squirrel cage induction motor |
| B. | Scharge motor |
| C. | Synchronous motor |
| D. | Hysteresis motor |
| Answer» D. Hysteresis motor | |
| 149. |
An alternator having 20 poles and running at 600 rpm will generate alternating voltage and current whose frequency is: |
| A. | 300 Hz |
| B. | 100 Hz |
| C. | 50 Hz |
| D. | 200 Hz |
| Answer» C. 50 Hz | |
| 150. |
Hydraulic torque transmission system is analog of _________ |
| A. | RC parallel circuit |
| B. | Motor generator set |
| C. | Amplidyne set |
| D. | None of these |
| Answer» C. Amplidyne set | |