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

During starting, windings are connected in wye (star), reducing the voltage across each winding to approximately 1/√3 (58%) of line voltage and reducing inrush current.

Question 2

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

Accepted Answer

1800 RPM

Answer

Synchronous speed = (120 × frequency) / number of poles = (120 × 60) / 4 = 1800 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

PLCs execute ladder logic or other programs to automate starting sequences, interlocks, and process control functions for motor systems.

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

Slip = (synchronous speed − actual speed) / synchronous speed × 100 = (1800 − 1750) / 1800 × 100 = 2.78%.

Question 5

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

Accepted Answer

NEMA 4

Answer

NEMA 4 enclosures are watertight and protect against hose-directed water from any direction, suitable for wash-down industrial environments.

(CEP) Certified Electrical Professional Practice Test

(CEP) Certified Electrical Professional Practice Test

CEP Motor Control & Drive Systems 2