Certified Energy Auditor Certification Motors, Drives, and Compressed Air 2

Question 1

A facility replaces a standard efficiency motor (90% efficient) with a premium efficiency motor (95% efficient) rated at 50 hp. Approximately how many kW does the premium motor save at full load?

Accepted Answer

1.97 kW

Answer

Power saved = 50 hp × 0.746 kW/hp × (1/0.90 − 1/0.95) ≈ 1.97 kW.

Question 2

Which motor nameplate parameter is most directly used to calculate full-load amperage for a single-phase motor?

Accepted Answer

Voltage, horsepower, and power factor

Answer

FLA = (hp × 746) / (V × PF × efficiency) — voltage, horsepower, and power factor are all required.

Question 3

A VFD reduces motor speed from 60 Hz to 48 Hz. By approximately what percentage does the motor's power consumption decrease (affinity laws)?

Accepted Answer

51%

Answer

Power ∝ (speed)³; (48/60)³ = 0.512, so power drops by ~51%.

Question 4

In a compressed air system, what is the primary purpose of an aftercooler?

Accepted Answer

Remove moisture from compressed air before storage

Answer

Aftercoolers cool hot discharge air, condensing moisture before it enters the receiver and distribution system.

Question 5

Which compressed air leak detection method is most practical for finding leaks during normal production operations?

Accepted Answer

Ultrasonic leak detection

Answer

Ultrasonic detectors can locate leaks safely in noisy, pressurized systems during normal operation without shutdown.

Certified Energy Auditor Certification Practice Test

Certified Energy Auditor Certification Practice Test

Certified Energy Auditor Certification Motors, Drives, and Compressed Air 2