CME CME Power Quality & Energy Efficiency 1 — Questions and Answers
Question 1: What is the acceptable range of Total Harmonic Distortion (THD) for voltage at a point of common coupling per IEEE 519?
- Less than 5% (Correct answer)
- Less than 10%
- Less than 15%
- Less than 20%
Correct answer: Less than 5%
IEEE 519 specifies that voltage THD at the point of common coupling should be less than 5% for systems below 69 kV.
Question 2: Which device is most effective for mitigating voltage sags caused by motor starting on a distribution system?
- Static VAR compensator (SVC) (Correct answer)
- Surge arrestor
- Ground fault relay
- Overcurrent relay
Correct answer: Static VAR compensator (SVC)
A static VAR compensator rapidly injects or absorbs reactive power to stabilize voltage during transient events like motor starting.
Question 3: A facility's power factor is measured at 0.72 lagging. What is the most efficient corrective action for a master electrician to recommend?
- Install capacitor banks at the load (Correct answer)
- Add resistive heating loads
- Install additional transformers
- Replace conductors with larger gauge
Correct answer: Install capacitor banks at the load
Capacitor banks supply leading reactive current that cancels the lagging reactive demand, improving power factor toward unity.
Question 4: Which harmonic order is typically the most problematic in three-phase systems powered by six-pulse VFDs?
- 5th and 7th (Correct answer)
- 2nd and 4th
- 3rd and 9th
- 11th and 13th
Correct answer: 5th and 7th
Six-pulse rectifier drives characteristically generate dominant 5th and 7th order harmonics that can overheat transformers and trip protective relays.
Question 5: What is the purpose of a K-factor rating on a transformer serving nonlinear loads?
- Indicates the transformer's ability to handle harmonic heating without derating (Correct answer)
- Defines the transformer's short-circuit withstand rating
- Specifies the maximum inrush current tolerance
- Sets the insulation voltage class
Correct answer: Indicates the transformer's ability to handle harmonic heating without derating
A K-factor transformer is designed with additional thermal capacity to withstand the increased eddy current losses caused by harmonic currents.
Question 6: Under ASHRAE 90.1, which lighting control strategy is REQUIRED for commercial spaces greater than 5,000 sq ft?
- Automatic shutoff controls (Correct answer)
- Dimmable ballasts only
- Occupancy sensors only
- Daylight harvesting only
Correct answer: Automatic shutoff controls
ASHRAE 90.1 mandates automatic shutoff controls (occupancy sensors or time scheduling) for commercial spaces exceeding 5,000 sq ft to reduce energy waste.
CME CME Power Quality & Energy Efficiency 1
What is the acceptable range of Total Harmonic Distortion (THD) for voltage at a point of common coupling per IEEE 519?