Electrical Drives - Basic Level Quiz

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