CEP Motor Control & Drive Systems 2

Question 1

In a star-delta (wye-delta) motor starting method, the motor windings are initially connected in:

Accepted Answer

Star (wye) configuration, reducing voltage across each winding to approximately 58% of line voltage

Answer

Delta configuration at reduced voltage

Answer

Parallel configuration for reduced current draw

Answer

Series configuration at full line voltage

Question 2

The synchronous speed of a 4-pole AC induction motor operating on a 60 Hz supply is:

Accepted Answer

1800 RPM

Answer

900 RPM

Answer

1200 RPM

Answer

3600 RPM

Question 3

What is the primary role of a programmable logic controller (PLC) in a motor control system?

Accepted Answer

To automate and sequence motor control operations based on programmed logic and input signals

Answer

To convert AC power to DC power for motor drives

Answer

To measure and log motor winding insulation resistance

Answer

To provide power factor correction for motor loads

Question 4

A motor has a synchronous speed of 1800 RPM and runs at an actual speed of 1750 RPM. What is the motor's slip?

Accepted Answer

2.78%

Answer

1.4%

Answer

4.17%

Answer

6.25%

Question 5

Which NEMA enclosure type is rated 'watertight' and protects motor control equipment against hose-directed water?

Accepted Answer

NEMA 4

Answer

NEMA 1

Answer

NEMA 3R

Answer

NEMA 12

Question 6

Regenerative braking in a VFD system works by:

Accepted Answer

Converting the motor's kinetic energy back into electrical energy returned to the power supply

Answer

Applying mechanical friction brakes to the motor shaft

Answer

Short-circuiting the motor terminals to create braking torque

Answer

Using dynamic braking resistors to dissipate energy as heat

Question 7

What is the primary purpose of a dynamic braking resistor (DBR) connected to a VFD?

Accepted Answer

To absorb and dissipate as heat the energy generated when the motor decelerates

Answer

To limit motor starting current during acceleration

Answer

To improve the power factor of the motor branch circuit

Answer

To provide emergency backup power during a supply failure