Answer: B. Motor and load motion. An electric drive combines a motor and control equipment to provide controlled mechanical motion to a load.
Which is a common electric-drive component?
A Heat exchanger only
B Mechanical brake only
C Power converter
D Fuel injector
Answer: C. Power converter. A drive commonly includes a motor, power converter, controller, sensors and mechanical load.
What does adjustable-speed control change?
A Cable insulation class
B Transformer polarity
C Motor operating speed
D Bearing material
Answer: C. Motor operating speed. Adjustable-speed control changes the motor speed to meet the process requirement.
What does motoring operation do?
A Converts motion to heat only
B Stores all input energy
C Converts electricity to motion
D Blocks motor current
Answer: C. Converts electricity to motion. In motoring, electrical input produces mechanical output at the shaft.
What happens during regenerative braking?
A Energy heats a resistor only
B Energy returns to supply
C Motor disconnects permanently
D Speed must increase
Answer: B. Energy returns to supply. A regenerative drive converts mechanical energy into electrical energy and sends it back to a receptive source.
Where is energy dissipated in dynamic braking?
A Gate driver
B Braking resistor
C Rotor bearings
D DC source only
Answer: B. Braking resistor. In dynamic braking, generated energy is dissipated as heat in a resistor.
What does plugging do to brake a motor?
A Applies reverse torque
B Removes all torque
C Raises synchronous speed
D Opens the field winding
Answer: A. Applies reverse torque. Plugging reverses the effective torque direction to produce rapid braking, with high current unless limited.
In a separately excited DC motor, how is its field supplied?
A Only by armature current
B By a rotor capacitor
C By load torque
D Independent field source
Answer: D. Independent field source. A separately excited motor has field and armature circuits supplied independently.
At constant flux, DC motor torque mainly follows which quantity?
A Armature resistance only
B Shaft speed only
C Supply frequency
D Armature current
Answer: D. Armature current. For a DC motor, electromagnetic torque is proportional to flux times armature current; with constant flux it follows armature current.
What is back EMF in a DC motor?
A Gate-driver voltage
B Rotor leakage current
C Mechanical friction torque
D Generated armature voltage
Answer: D. Generated armature voltage. Rotation induces an armature voltage that opposes the applied voltage and is called back EMF.
What is a common effect of weakening DC motor field?
A Higher speed, lower torque
B Lower speed, higher torque
C Zero back EMF
D Fixed speed only
Answer: A. Higher speed, lower torque. Reducing field flux allows higher speed above base speed, but available torque falls for a given armature current.
How does a controlled rectifier regulate a DC drive?
A Changes bearing clearance
B Reverses shaft position
C Adjusts armature voltage
D Sets rotor resistance only
Answer: C. Adjusts armature voltage. A controlled rectifier varies the average DC voltage applied to the motor armature.
What does a DC chopper control in a DC drive?
A Motor pole count
B Field insulation color
C Average armature voltage
D Mechanical load inertia
Answer: C. Average armature voltage. A chopper changes the average armature voltage by varying its switching duty ratio.
What does closed-loop speed control use?
A Only a fixed resistor
B No reference input
C A mechanical clutch
D Speed feedback
Answer: D. Speed feedback. Closed-loop control compares measured speed with a reference and corrects the resulting error.
Which sensor can measure motor speed?
A Thermistor only
B Current transformer
C Strain gauge
D Tachogenerator
Answer: D. Tachogenerator. A tachogenerator produces a signal related to shaft speed.
Why is a fast current loop used in many drives?
A Control torque and protect
B Set bearing lubrication
C Increase pole count
D Measure insulation resistance
Answer: A. Control torque and protect. Motor torque is closely related to current, and a fast current loop can limit overcurrent and improve torque response.
Below base speed, many drives provide approximately what capability?
A Constant power only
B Constant torque
C Constant slip only
D Zero torque
Answer: B. Constant torque. With rated flux and current limits, a motor drive commonly operates in a constant-torque region below base speed.
How is induction-motor synchronous speed calculated?
A 120f divided by poles
B Poles divided by 120f
C Frequency times slip
D Voltage divided by current
Answer: A. 120f divided by poles. Synchronous speed in rpm equals 120 times supply frequency divided by the number of poles.
What is induction-motor slip?
A Rotor current ratio
B Speed difference fraction
C Torque per pole
D Voltage drop fraction
Answer: B. Speed difference fraction. Slip is the difference between synchronous speed and rotor speed divided by synchronous speed.
What does constant V/f control aim to maintain?
A Rotor temperature
B Shaft inertia
C Air-gap flux
D Bearing pressure
Answer: C. Air-gap flux. Below base frequency, keeping voltage-to-frequency ratio roughly constant maintains motor flux approximately constant.
How does a variable-frequency drive change motor speed?
A Changes supply frequency
B Changes shaft diameter
C Changes pole material
D Changes bearing clearance
Answer: A. Changes supply frequency. Changing stator supply frequency changes the induction motor synchronous speed.
What does a stepper motor do for each pulse?
A Moves a defined step
B Changes insulation class
C Reverses supply frequency
D Stops all rotor flux
Answer: A. Moves a defined step. A stepper motor advances by a discrete angle in response to its commanded pulse sequence.
What is a common servo-drive feature?
A Uncontrolled fixed speed
B No feedback sensor
C Only thermal protection
D Closed-loop motion control
Answer: D. Closed-loop motion control. A servo drive uses feedback to regulate a motion variable such as position, speed or torque.
What is a common purpose of overload protection?
A Protect motor from overheating
B Increase synchronous speed
C Improve rotor balance
D Set the load torque
Answer: A. Protect motor from overheating. Overload protection limits excessive current or thermal stress that could damage motor insulation.
What does motor-load coupling transmit?
A Gate pulses
B Mechanical torque
C Line frequency
D Field voltage
Answer: B. Mechanical torque. A coupling transfers shaft torque from the motor to the driven load.