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ETO Multiple Choice Questions :- Electro-Technical Officer
1) PLCs are _____________ designed for use in the control of a wide variety of manufacturing machines and systems.
A. special-purpose industrial computers
B. personal computers
C. electromechanical systems
D. All of the above
Answer: A
2) The PLC was invented by _____________.
A. Bill Gates
B. Dick Morley
C. Bill Landis
D. Tod Cunningham
Answer: B
3) The first company to build PLCs was _____________.
A. General Motors
B. Allen Bradley
C. Square D
D. Modicon
Answer: D
4) Which of the following statements is not correct?
A. The PLC rung output [-( )-] is a discrete output instruction or bit in memory.
B. Each rung of the ladder logic represents a logical statement executed in software – inputs on the right and outputs on the left.
C. Input and output instructions in ladder logic do not directly represent the switches and actuators.
D. PLC input instructions are logical symbols associated with voltage at the input module terminals.
Answer: B
5) Which of the following statements is correct?
A. Ladder logic is a PLC graphical programming technique introduced in the last 10 years.
B. A ladder logic program is hard to analyze because it is totally different when compared with the equivalent relay logic solution.
C. The number of ladder logic virtual relays and input and output instructions is limited only by memory size.
D. The number of contacts for a mechanical relay is limited to number of coils on the relay.
Answer: C
6) Which of the following statements is NOT correct?
A. The status of each input can be checked from one location and outputs can be forced on and off.
B. All symbols in the RLL represent actual components and contacts present in the control system.
C. PLCs are not as reliable as electromechanical relays in RLL.
D. Input (-| |-) and output (- ( ) -) instruction symbols in the ladder logic represent only data values stored in PLC memory.
Answer: C
7) Which of the following statements is NOT correct?
A. If a problem in a PLC module occurs, the module can be changed in a matter of minutes without any changes in wiring.
B. Outputs can be paralleled on the same rung.
C. The physical wires between the input and output field devices and the PLC input and output modules are the only signal wires required in the PLC system.
D. The cost and size of PLCs have increased significantly in the last 10 years.
Answer: D
8) Which of the following statements about a single pole double throw relay is NOT true?
A. It is called an SPDT type of relay.
B. It has one common contact.
C. It has two positions (NC and NO).
D. It has a center off position.
Answer: D
9) Which of the following statements about a single pole double throw relay is true?
A. Insulators are used in the armature to isolate the electrical switching
contacts from the rest of the relay components.
B. The NC contact and the pole are in contact when the relay is off.
C. It has just one coil.
D. All of the above.
Answer: D
10) Which of the following statements about RLL is NOT true?
A. NO contact symbol has two parallel lines to indicate an open contact.
B. RLL stands for Relay Ladder LogiC.
C. NC contact symbol has the same two parallel lines with a line across them to indicate closed contacts.
D. The right power rail is positive or the high side of the source, and the left power rail is the power return or grounD.
Answer: D
11) The ______________ is moved toward the relay electromagnet when the relay is on.
A. Armature
B. Coil
C. NO contact
D. NC contact
Answer: A
12) When a relay is NOT energized:
A. There is an electrical path through the NO contacts
B. There is an electrical path through the NC contacts
C. Neither the NO or the NC contacts have an electrical path
D. Both the NO and the NC contacts have an electrical path
Answer: B
13) Which of the following RLL applications is not normally performed in early automation systems?
A. On/off control of field devices
B. Logical control of discrete devices
C. On/off control of motor starters
D. Proportional control of field devices
Answer: D
14) Current flows into the ___________.
A. Input terminal of a sinking DC input module
B. Input terminal of a sinking output field device
C. Output terminal of a sinking input field device
D. All of the above
Answer: D
15) In a current sinking DC input module _____________.
A. The current flows out of the input field device
B. Requires that a AC sources be used with mechanical switches
C. The current flows out of the input module
D. Currents can flow in either direction at the input module
Answer: A
16) AC output field devices can interface to _______________.
A. AC output modules
B. Relay output modules
C. Both a and b
D. Neither a or b
Answer: C
17) What one item in the output module circuit above should be changed to make it correct.
A. The battery polarity
B. Output module should be sourcing
C. Field device should be sinking
D. Current flow direction
Answer: D
18) What one item in the input module circuit above should be changed to make it correct.
A. The battery polarity
B. Input module should be sinking
C. Field device should be sinking
D. Current flow direction
Answer: B
19. In an open loop control system
A. Output is independent of control input
B. Output is dependent on control input
C. Only system parameters have effect on the control output
D. None of the above
Answer: A
20. For open control system which of the following statements is incorrect ?
A. Less expensive
B. Recalibration is not required for maintaining the required quality of the output
C. Construction is simple and maintenance easy
D. Errors are caused by disturbances
Answer: B
21. A control system in which the control action is somehow dependent on the output is known as
A. Closed loop system
B. Semiclosed loop system
C. Open system
D. None of the above
Answer: A
22. In closed loop control system, with positive value of feedback gain the overall gain of the system will
A. decrease
B. increase
C. be unaffected
D. any of the above
Answer: A
23. Which of the following is an open loop control system ?
A. Field controlled D.C. motor
B. Ward leonard control
C. Metadyne
D. Stroboscope
Answer: A
24. Which of the following statements is not necessarily correct for open control system ?
A. Input command is the sole factor responsible for providing the control action
B. Presence of non-linearities causes malfunctioning
C. Less expensive
D. Generally free from problems of non-linearities
Answer: B
25. In open loop system
A. the control action depends on the size of the system
B. the control action depends on system variables
C. the control action depends on the input signal
D. the control action is independent of the output
Answer: D
26. has tendency to oscillate.
A. Open loop system
B. Closed loop system
C. Both A. and B.
D. Neither A. nor B.
Answer: B
27. A good control system has all the following features except
A. good stability
B. slow response
C. good accuracy
D. sufficient power handling capacity
Answer: B
28. The initial response when the output is not equal to input is called
A. Transient response
B. Error response
C. Dynamic response
D. Either of the above
Answer: A
29. A control system working under unknown random actions is called
A. computer control system
B. digital data system
C. stochastic control system
D. adaptive control system
Answer: C
30. Any externally introduced signal affecting the controlled output is called a
A. feedback
B. stimulus
C. signal
D. gain control
Answer: B
31. A closed loop system is distinguished from open loop system by which of the following ?
A. Servomechanism
B. Feedback
C. Output pattern
D. Input pattern
Answer: B
32. Which of the following devices are commonly used as error detectors in instruments ?
A. Vernistats
B. Microsyns
C. Resolvers
D. Any of the above
Answer: D
33. Which of the following should be done to make an unstable system stable ?
A. The gain of the system should be decreased
B. The gain of the system should be increased
C. The number of poles to the loop transfer function should be increased
D. The number of zeros to the loop transfer function should be increased
Answer: B
34. increases the steady state accuracy.
A. Integrator
B. Differentiator
C. Phase lead compensator
D. Phase lag compensator
Answer: A
35. A.C. servomotor resembles
A. two phase induction motor
B. Three phase induction motor
C. direct current series motor
D. universal motor
Answer: A
36. As a result of introduction of negative feedback which of the following will not decrease ?
A. Band width
B. Overall gain
C. Distortion
D. Instability
Answer: A
37. Regenerative feedback implies feedback with
A. oscillations
B. step input
C. negative sign
D. positive sign
Answer: D
38. The output of a feedback control system must be a function of
A. reference and output
B. reference and input
C. input and feedback signal
D. output and feedback signal
Answer: A
39. is an open loop control system.
A. Ward Leonard control
B. Field controlled D.C. motor
C. Stroboscope
D. Metadyne
Answer: B
40. A control system with excessive noise, is likely to suffer from
A. saturation in amplifying stages
B. loss of gain
C. vibrations
D. oscillations
Answer: A
41. Zero initial condition for a system means
A. input reference signal is zero
B. zero stored energy
C. ne initial movement of moving parts
D. system is at rest and no energy is stored in any of its components
Answer: D
42. Transfer function of a system is used to calculate which of the following ?
A. The order of the system
B. The time constant
C. The output for any given input
D. The steady state gain
Answer: C
43. The band width, in a feedback amplifier.
A. remains unaffected
B. decreases by the same amount as the gain increase
C. increases by the sane saaaajajt as the gain decrease
D. decreases by the same amount as the gain decrease
Answer: C
44. On which of the following factors does the sensitivity of a closed loop system to gain changes and load disturbances depend ?
A. Frequency
B. Loop gain
C. Forward gain
D. All of the above
Answer: D
45. The transient response, with feedback system,
A. rises slowly
B. rises quickly
C. decays slowly
D. decays quickly
Answer: D
46. The second derivative input signals modify which of the following ?
A. The time constant of the system
B. Damping of the system
C. The gain of the system
D. The time constant and suppress the oscillations
E. None of the above
Answer: D
47. Which of the following statements is correct for any closed loop system ?
A. All the co-efficients can have zero value
B. All the co-efficients are always non-zero
C. Only one of the static error co-efficients has a finite non-zero value
D. None of the above
Answer: C
48. Which of the following statements is correct for a system with gain margin close to unity or a phase margin close to zero ?
A. The system is relatively stable
B. The system is highly stable
C. The system is highly oscillatory
D. None of the above
Answer: C
49. Due to which of the following reasons excessive bond width in control systems should be avoided ?
A. It leads to slow speed of response
B. It leads to low relative stability
C. Noise is proportional to band width
D. None of the above
Answer: C
50. In a stable control system backlash can cause which of the following ?
A. Underdamping
B. Overdamping
C. Poor stability at reduced values of open loop gain
D. Low-level oscillations
Answer: D
51. In an automatic control system which of the following elements is not used ?
A. Error detector
B. Final control element
C. Sensor
D. Oscillator
Answer: D
52. In a control system the output of the controller is given to
A. final control element
B. amplifier
C. comparator
D. sensor
E. none of the above
Answer: A
53. A controller, essentially, is a
A. sensor
B. clipper
C. comparator
D. amplifier
Answer: C
54. Which of the following is the input to a controller ?
A. Servo signal
B. Desired variable value
C. Error signal
D. Sensed signal
Ans:
55. The on-off controller is a _____ system.
A. digital
B. linear
C. non-linear
D. discontinuous
Ans:
56. The capacitance, in force-current analogy, is analogous to
A. momentum
B. velocity
C. displacement
D. mass
Answer: D
57. The temperature, under thermal and electrical system analogy, is considered analogous to
A. voltage
B. current
C. capacitance
D. charge
E. none of the above
Answer: A
58. In electrical-pneumatic system analogy the current is considered analogous to
A. velocity
B. pressure
C. air flow
D. air flow rate
Answer: D
59. In liquid level and electrical system analogy, voltage is considered analogous to
A. head
B. liquid flow
C. liquid flow rate
D. none of the above
Answer: A
60. The viscous friction co-efficient, in force-voltage analogy, is analogous to
A. charge
B. resistance
C. reciprocal of inductance
D. reciprocal of conductance
E. none of the above
Answer: B
61. In force-voltage analogy, velocity is analogous to
A. current
B. charge
C. inductance
D. capacitance
Answer: A
62. In thermal-electrical analogy charge is considered analogous to
A. heat flow
B. reciprocal of heat flow
C. reciprocal of temperature
D. temperature
E. none of the above
Answer: D
63. Mass, in force-voltage analogy, is analogous to
A. charge
B. current
C. inductance
D. resistance
Answer: C
64. The transient response of a system is mainly due to
A. inertia forces
B. internal forces
C. stored energy
D. friction
Answer: C
65. signal will become zero when the feedback signal and reference signs are equal.
A. Input
B. Actuating
C. Feedback
D. Reference
Answer: B
66. A signal other than the reference input that tends to affect the value of controlled variable is known as
A. disturbance
B. command
C. control element
D. reference input
Answer: A
67. The transfer function is applicable to which of the following ?
A. Linear and time-in variant systems
B. Linear and time-variant systems
C. Linear systems
D. Non-linear systems
E. None of the above
Answer: A
68. From which of the following transfer function can be obtained ?
A. Signal flow graph
B. Analogous table
C. Output-input ratio
D. Standard block system
E. None of the above
Answer: A
69. is the reference input minus the primary feedback.
A. Manipulated variable
B. Zero sequence
C. Actuating signal
D. Primary feedback
Answer: C
70. The term backlash is associated with
A. servomotors
B. induction relays
C. gear trains
D. any of the above
Answer:
71. With feedback _____ increases.
A. system stability
B. sensitivity
C. gain
D. effects of disturbing signals
Answer: A
72. By which of the following the system response can be tested better ?
A. Ramp input signal
B. Sinusoidal input signal
C. Unit impulse input signal
D. Exponentially decaying signal
Answer: C
73. In a system zero initial condition means that
A. The system is at rest and no energy is stored in any of its components
B. The system is working with zero stored energy
C. The system is working with zero reference signal
Answer: A
74. Spring constant in force-voltage analogy is analogous to
A. capacitance
B. reciprocal of capacitance
C. current
D. resistance
Answer: B
75. An increase in gain, in most systems, leads to
A. smaller damping ratio
B. larger damping ratio
C. constant damping ratio
D. none of the above
Answer: A
76. A conditionally stable system exhibits poor stability at
A. low frequencies
B. reduced values of open loop gain
C. increased values of open loop gain
D. none of the above
Answer: B
77. If a step function is applied to the input of a system and the output remains below a certain level for all the time, the system is
A. not necessarily stable
B. stable
C. unstable
D. always unstable
E. any of the above
Answer: A
78. Addition of zeros in transfer function causes which of the following ?
A. Lead-compensation
B. Lag-compensation
C. Lead-lag compensation
D. None of the above
Answer: B
79. In order to increase the damping of a badly underdamped system which of following compensators may be used ?
A. Phase-lead
B. Phase-lag
C. Both A. and B.
D. Either A. and B.
E. None of the above
Answer: A
80. The phase lag produced by transportation relays
A. is independent of frequency
B. is inverseh’proportional to frequency
C. increases linearly with frequency
D. decreases linearly with frequency
Answer: C
81. In a stable control system saturation can cause which of the following ?
A. Low-level oscillations
B. High-level oscillations
C. Conditional stability
D. Overdamping
Answer: A
82. Which of the following can be measured by the use of a tacho-generator ?
A. Acceleration
B. Speed
C. Speed and acceleration
D. Displacement
E. None of the above
Answer: B
83 is not a final control element.
A. Control valve
B. Potentiometer
C. Electro-pneumatic converter
D. Servomotor
Answer: B
84. Which of the following is the definition of proportional band of a controller ?
A. The range of air output as measured variable varies from maximum to minimum
B. The range of measured variables from set value
C. The range of measured variables through which the air output changes from maximum to minimum
D. Any of the above
E. None of the above
Answer: C
85. In pneumatic control systems the control valve used as final control element converts
A. pressure signal to electric signal
B. pressure signal to position change
C. electric signal to pressure signal
D. position change to pressure signal
E. none of the above
Answer: B
86. Pressure error can be measured by which of the following ?
A. Differential bellows and straingauge
B. Selsyn
C. Strain gauge
D. Strain gauge and potentiometer
Answer: A
87. The effect of error damping is to
A. provide larger settling lime
B. delay the response
C. reduce steady state error
D. any of the above
E. none of the above
Answer: C
88. Which of the following is the non-linearity caused by servomotor ?
A. Static friction
B. Backlash
C. Saturation
D. None of the above
Answer: C
89. Which of the following is an electromechanical device ?
A. Induction relay
B. Thermocouple
C. LVDT
D. Any of the above
E. None of the above
Answer: C
90. A differentiator is usually not a part of a control system because it
A. reduces damping
B. reduces the gain margin
C. increases input noise
D. increases error
Answer: C
91. If the gain of the critical damped system is increased it will behave as
A. oscillatory
B. critically damped
C. overdamped
D. underdamped
E. none of the above
Answer: D
92. In a control system integral error compensation _______ steady state error
A. increases
B. minimizes
C. does not have any effect on
D. any of the above
Answer: B
93. With feed back _____ reduces.
A. system stability
B. system gain
C. system stability and gain
D. none of the above
Answer: B
94. Which of the following can be measured by LVDT?
A. Displacement
B. Velocity
C. Acceleration
D. Any of the above
Answer: D
95. directly converts temperature into voltage.
A. Thermocouple
B. Potentiometer
C. Gear train
D. LVDT
E. None of the above
Answer: A
96. Which of the following is the output of a thermocouple ?
A. Alternating current
B. Direct current
C. A.C. voltage
D. D.C. voltage
E. None of the above
Answer: D
97. A.C. servomotor is basically a
A. universal motor
B. single phase induction motor
C. two phase induction motor
D. three phase induction motor
Answer: C
98. Maximum demand controller is used to ___________.
A. switch off essential loads in a logical sequence
B. exceed the demand of the plant
C. switch off non-essential loads in a logical sequence
D. controls the power factor of the plant
Answer: C
99. Capacitors with automatic power factor controller when installed in a plant:
A. reduces active power drawn from grid
B. reduces the reactive power drawn from grid
C. reduces the voltage of the plant
D. increases the load current of the plant
Answer: B
100. Eddy current drive can be a retrofit for ________.
A. constant speed system requirement
B. variable speed system requirement
C. dual speed system requirement only
D. none of the above
Answer: B
101. Electronic variable frequency drive (VFD. connected to motors:
A. provide variable speed with high efficiency
B. induces eddy-current in the secondary member of the clutch mechanism
C. is not suitable for variable torque load
D. does not provide variable speed and has low-efficiency
Answer: A
102. The basic functions of electronic ballast excludes one of the following:
A. to ignite the lamp
B. to stabilize the gas discharge
C. to reduce lumen output of the lamp
D. to supply power to the lamp
Answer: C
103. The characteristic of conventional ballast in lighting application is one among the following:
A. They have low operational losses than electronic ballasts.
B. They have tuned circuit to deliver power at 25 Hz
C. They do not require a mechanical switch (starter)
D. They have high operational losses and high temperature rise
Answer: D
104. Electronic soft starters are used for motors to:
A. achieve variable speed
B. provide smooth start and stop
C. improve the loading
D. none of the above
Answer: B
105 .The two windings of a transformer is
A. conductively linkeD.
B. inductively linkeD.
C. not linked at all.
D. electrically linkeD.
Ans : b
106. A salient pole synchronous motor is running at no loaD. Its field current is switched off. The motor will
A. come to stop.
B. continue to run at synchronous speeD.
C. continue to run at a speed slightly more than the synchronous speeD.
D. continue to run at a speed slightly less than the synchronous speeD.
Answer: B.
107. The D.C. series motor should always be started with load because
A. at no load, it will rotate at dangerously high speeD.
B. it will fail to start.
C. it will not develop high starting torque.
D. all are true.
Answer: A
108. The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load speed is about
A. 50 Hz
B. 20 Hz.
C. 2 Hz
D. Zero.
Answer: C
109. In a stepper motor the angular displacement
A. can be precisely controlleD.
B. it cannot be readily interfaced with micro computer based controller.
C. the angular displacement cannot be precisely controlleD.
D. it cannot be used for positioning of work tables and tools in NC machines.
Answer: A
110. The power factor of a squirrel cage induction motor is
A. low at light load only.
B. low at heavy load only.
C. low at light and heavy load both.
D. low at rated load only.
Answer: A
111. When a synchronous motor is running at synchronous speed, the damper winding produces
A. damping torque.
B. eddy current torque.
C. torque aiding the developed torque.
D. no torque.
Answer: D
112 . In a 3 – phase induction motor the maximum torque
A. is proportional to rotor resistance r2 .
B. does not depend on r2 .
C. is proportional to r2 .
D. is proportional to 2 r2 .
Answer: B
113. In a D.C. machine, the armature mmf is
A. stationary w.r.t. armature.
B. rotating w.r.t. fielD.
C. stationary w.r.t. fielD.
D. rotating w.r.t. brushes.
Answer: C
114. In a transformer the voltage regulation will be zero when it operates at
A. unity p.f.
B. leading p.f.
C. lagging p.f.
D. zero p.f. leading.
Answer: B
115. The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for a
A. dc machine.
B. 3 phase induction machine.
C. synchronous machine.
D. single phase induction machine.
E. all the above
Answer: E
116. The current from the stator of an alternator is taken out to the external load circuit through
A. slip rings
B. commutator segments.
C. solid connections.
D. carbon brushes.
Answer: C
117. A motor which can conveniently be operated at lagging as well as leading power factors is the
A. squirrel cage induction motor.
B. wound rotor induction motor.
C. synchronous motor.
D. DC shunt motor.
Answer: C
118. The most suitable servomotor for low power applications is
A. a dc series motor.
B. a dc shunt motor.
C. an ac two-phase induction motor.
D. an ac series motor.
Answer: B.
119. The size of a conductor used in power cables depends on the
A. operating voltage.
B. power factor.
C. current to be carried
D. type of insulation useD.
Answer: C.
120. Out of the following methods of heating the one which is independent of supply frequency is
A. electric arc heating
B. induction heating
C. electric resistance heating
D. dielectric heating
Answer: C.
121. An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be
A. less.
B. more.
C. more or less.
D. the same.
Answer: B.
122. Inverse definite minimum time lag relay is also called ___________
A. pilot relay.
B. differential relay.
C. over current relay.
D. directional overcurrent relay.
Answer: B.
123. The polarity test is not necessary for the single-phase transformer so as to correctly determine _____________of the transformer.
A. shunt branch parameters.
B. transformation ratio.
C. series parameters.
D. any of the above characteristics.
Answer: D.
124. The speed-torque characteristics of a DC series motor are approximately similar to those of the _________motor.
A. universal
B. synchronous
C. DC shunt
D. two-phase
Answer: A
125. The torque-speed characteristics of an A.C. operated universal motor has a ______characteristic and it______ be started under no-load condition.
A. inverse, can
B. nearly inverse, can
C. inverse, cannot
D. nearly inverse, cannot
Answer: C
126. In the heating process of the ________type a simple method of temperature control is possible by means of a special alloy which loses its magnetic properties at a particular high temperature and regains them when cooled to a temperature below this value.
A. Indirect induction over
B. core type induction furnace
C. coreless induction furnace
D. high frequency eddy current
Answer: D.
127. In order to reduce the harmful effects of harmonics on the A.C. side of a high voltage D.C. transmission system ______are provideD.
A. synchronous condensers
B. shunt capacitors
C. shunt filters
D. static compensators
Answer: C.
128. An A.C. tachometer is just a ________with one phase excited from the carrier frequency.
A. two-phase A.C. servomotor
B. two-phase induction motor
C. A.C. operated universal motor
D. hybrid stepper motor.
Answer: D
129. A commutator in a D.C. machine
A. Reduces power loss in armature.
B. Reduces power loss in field circuit.
C. Converts the induced A.c armature voltage into direct voltage.
D. Is not necessary.
Answer: C
130. A ceiling fan uses
A. split-phase motor.
B. capacitor start and capacitor run motor.
C. universal motor.
D. capacitor start motor.
Answer: D.
To give starting torque and to maintain speeD.
131. A stepper motor is
A. a dc motor.
B. a single-phase ac motor.
C. a multi-phase motor.
D. a two phase motor.
Answer: D.
132. The ‘sheath’ is used in cable to
A. provide strength to the cable.
B. provide proper insulation.
C. prevent the moisture from entering the cable.
D. avoid chances of rust on strands.
Answer: A.
133. The drive motor used in a mixer-grinder is a
A. dc motor.
B. induction motor.
C. synchronous motor.
D. universal motor.
Answer: D.
134. In a 3-phase synchronous motor
A. the speed of stator MMF is always more than that of rotor MMF.
B. the speed of stator MMF is always less than that of rotor MMF.
C. the speed of stator MMF is synchronous speed while that of rotor MMF is zero.
D. rotor and stator MMF are stationary with respect to each other.
Answer: D.
135. In a capacitor start single-phase induction motor, the capacitor is connected
A. in series with main winding.
B. in series with auxiliary winding.
C. in series with both the windings.
D. in parallel with auxiliary winding.
Answer: B
136. A synchro has
A. a 3-phase winding on rotor and a single-phase winding on stator.
B. a 3-phase winding on stator and a commutator winding on rotor.
C. a 3-phase winding on stator and a single-phase winding on rotor.
D. a single-phase winding on stator and a commutator winding on rotor.
Answer: C
137. As the voltage of transmission increases, the volume of conductor
A. increases
B. does not change.
C. decreases.
D. increases proportionately.
Answer: C
138. The size of the feeder is determined primarily by
A. the current it is required to carry.
B. the percent variation of voltage in the feeder.
C. the voltage across the feeder.
D. the distance of transmission.
Ans a
139. To achieve low PT error, the burden value should be ____________.
A. low
B. high
C. medium
D. none of the above
Answer: A
140. The synchronous reactance of the synchronous machine is ______________.
A. Ratio between open circuit voltage and short circuit current at constant field current
B. Ratio between short circuit voltage and open circuit current at constant field current
C. Ratio between open circuit voltage and short circuit current at different field current
D. Ratio between short circuit voltage and open circuit current at different field current
Ans. A.
141. In case of a universal motor, torque pulsation is minimized by _________.
A. load inertia
B. rotor inertia
C. both rotor and load inertia
D. none of the above
Answer: C
142. The efficiency of a transformer is mainly dependent on
A. core losses
B. copper losses.
C. stray losses.
D. dielectric losses.
Answer: A