Electrical Systems & Power Quality Flashcards

What is the primary function of a Variable Frequency Drive (VFD) when applied to motor-driven systems?

Answer: To control motor speed by varying the frequency and voltage of the electrical supply

A VFD controls AC motor speed by varying the frequency and magnitude of the electrical supply, enabling significant energy savings when full motor speed is not required for the process.

In a three-phase electrical system, what does 'voltage unbalance' refer to?

Answer: Unequal voltage magnitudes or phase angle differences among the three phases

Voltage unbalance occurs when the voltage magnitudes or phase angles among the three phases are not equal, which causes additional heating in motors and can reduce motor efficiency and lifespan.

What is a key benefit of installing electrical sub-metering within a large commercial or industrial facility?

Answer: It enables identification of energy consumption by individual systems, departments, or equipment

Sub-metering provides granular, real-time energy consumption data at the system or department level, enabling energy managers to pinpoint inefficiencies and make targeted improvements.

What is the primary function of a soft starter connected to an AC motor?

Answer: To gradually ramp up voltage to the motor during startup, reducing inrush current and mechanical stress

A soft starter gradually increases the voltage applied to the motor during startup, reducing the inrush current (which can be 6–10× rated current) and minimizing mechanical stress on the motor and driven equipment.

Which standard provides the recommended harmonic current and voltage distortion limits for electrical power systems in the United States?

Answer: IEEE 519 - Recommended Practices for Harmonic Control in Electrical Power Systems

IEEE 519 establishes recommended limits for voltage and current harmonic distortion at the point of common coupling between a facility and the utility, guiding both utilities and customers.

In energy management, what is the primary objective of implementing a load shedding strategy?

Answer: To reduce peak electrical demand and lower utility demand charges during high-load periods

Load shedding strategies intentionally reduce non-critical electrical loads during peak demand periods to lower the recorded peak demand and reduce demand charges on utility bills.

Which lighting control technology reduces energy consumption by automatically adjusting artificial light levels based on the amount of available natural daylight?

Answer: Daylight harvesting controls with photosensors

Daylight harvesting controls use photosensors to measure available natural light and automatically dim or extinguish artificial lighting to maintain target illuminance levels while minimizing energy use.