Motors, Drives, and Compressed Air Flashcards
7 cards from real Certified Energy Auditor Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Motors, Drives, and Compressed Air flashcards as text
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?
Answer: 1.97 kW
Power saved = 50 hp × 0.746 kW/hp × (1/0.90 − 1/0.95) ≈ 1.97 kW.
Which motor nameplate parameter is most directly used to calculate full-load amperage for a single-phase motor?
Answer: Voltage, horsepower, and power factor
FLA = (hp × 746) / (V × PF × efficiency) — voltage, horsepower, and power factor are all required.
A VFD reduces motor speed from 60 Hz to 48 Hz. By approximately what percentage does the motor's power consumption decrease (affinity laws)?
Answer: 51%
Power ∝ (speed)³; (48/60)³ = 0.512, so power drops by ~51%.
In a compressed air system, what is the primary purpose of an aftercooler?
Answer: Remove moisture from compressed air before storage
Aftercoolers cool hot discharge air, condensing moisture before it enters the receiver and distribution system.
Which compressed air leak detection method is most practical for finding leaks during normal production operations?
Answer: Ultrasonic leak detection
Ultrasonic detectors can locate leaks safely in noisy, pressurized systems during normal operation without shutdown.
A motor's service factor is listed as 1.15. What does this indicate?
Answer: The motor can run continuously at 115% of rated load without damage
A service factor of 1.15 means the motor can operate at 115% of its nameplate horsepower on a continuous basis.
When evaluating a multi-stage centrifugal compressor, which performance curve best describes the relationship between pressure and flow at constant speed?
Answer: Drooping curve — pressure decreases as flow increases
Centrifugal compressors have a drooping (falling) pressure-flow curve where discharge pressure decreases as flow rate increases.