WorksheetsElectrical Drives - Basic Level Quiz
Total questions: 20
Worksheet time: 10mins
A DC motor refuses to rotate when connected. What should you check first?
Field winding resistance
Armature voltage supply
PWM frequency
Power factor
Your induction motor hums but doesn’t start. What’s the likely reason?
Excessive load
Broken rotor bar
Open phase or starting capacitor fault
Over-voltage
A 3-phase motor runs in the opposite direction. What can correct this?
Add resistance
Increase frequency
Swap any two phase connections
Add filter
A DC drive system has erratic speed. What’s a likely cause?
Constant torque
Improper voltage feedback or loose potentiometer
High inertia
Balanced load
Your AC motor draws high current at startup. What control strategy can reduce this?
Line commutation
Star-delta starter
Short-circuit the stator
Open-loop V/f
A variable frequency drive (VFD) motor makes high-pitched noise. What is it due to?
Power loss
Mechanical imbalance
High switching frequency from the inverter
Faulty capacitor
When using regenerative braking, what happens to energy?
It’s dissipated as heat
Returned to the supply or battery
Lost in shaft
Consumed by rotor
A synchronous motor does not start on its own. How to solve this?
Reduce stator voltage
Add damper windings or auxiliary motor
Reverse direction
Decrease excitation
During operation, the drive overheats. What’s a common oversight?
Overload protection
Motor enclosure
Improper ventilation or cooling fan failure
Power factor correction
The motor keeps tripping after running for some time. What should you inspect?
Field weakening
Speed controller
Overload relay or thermal sensor
Step angle
A DC series motor is loaded without a load initially. What is the risk?
Low speed
High starting torque
Speed may reach dangerously high values
Low efficiency
A drive used in cranes must offer fast braking. Which method is best suited?
Dynamic braking
V/f control
Cycloconverter
PWM
Which motor is best suited for constant torque load?
Series DC motor
Shunt DC motor
Universal motor
Stepper motor
For fan applications, which torque-speed profile is ideal?
Constant torque
Constant power
Torque proportional to square of speed
Torque inversely proportional to speed
A drive used in CNC must allow precise position control. Ideal motor?
Induction motor
Stepper motor or servo motor
Universal motor
Synchronous reluctance motor
Which parameter increases when motor is under-loaded?
Power factor
Slip
Efficiency
Torque
When an induction motor runs above synchronous speed, it operates as:
Motor
Generator
Braking resistor
Reactor
Your drive is unable to maintain speed under load. Likely fault?
Incorrect encoder feedback or closed-loop gain
Improper V/f
Open stator
Inverter dead-time
Which device can control both direction and speed in DC drives?
Starters
Inverter
Chopper
Dual converter
For high-speed railway traction, which drive is commonly used?
DC shunt
AC induction with VFD
BLDC
Synchronous reluctance
