EETC Motor Controls 5

Question 1

What is regenerative braking in an AC drive system?

Accepted Answer

Returning braking energy back to the power supply instead of dissipating it as heat

Answer

Regenerative braking returns the motor's kinetic energy back to the AC supply line, improving energy efficiency compared to resistive braking.

Question 2

Which control component is used to detect that a motor has reached a specific speed before advancing to the next starting step?

Accepted Answer

Centrifugal speed switch or back-EMF relay

Answer

A centrifugal speed switch or back-EMF relay detects when the motor has accelerated to a set speed, triggering transition to the next starting step.

Question 3

What is the purpose of a phase sequence relay in a motor control circuit?

Accepted Answer

To detect incorrect phase rotation and prevent motor damage or reverse operation

Answer

A phase sequence relay monitors the order of three-phase voltages and trips if the sequence is incorrect, preventing a motor from running in the wrong direction.

Question 4

In DC injection braking, what stops an AC induction motor?

Accepted Answer

DC current injected into the stator creates a stationary magnetic field that brakes the rotor

Answer

DC injection braking applies a DC voltage to the AC stator windings, creating a stationary magnetic field that exerts a braking torque on the spinning rotor.

Question 5

A motor nameplate shows a service factor (SF) of 1.15. What does this indicate?

Accepted Answer

The motor can operate at 115% of rated horsepower under specified conditions without damage

Answer

A service factor of 1.15 means the motor can safely handle 15% overload beyond its nameplate horsepower rating under proper conditions.

(EETC) Electrical Technician Certification Practice Test

(EETC) Electrical Technician Certification Practice Test

EETC Motor Controls 5