CEP CEP Power Systems & Distribution 2 ā Questions and Answers
Question 1: What is the effect of a low power factor on an electrical distribution system?
- It reduces voltage drop
- It increases current draw for the same real power, increasing conductor losses (Correct answer)
- It improves transformer efficiency
- It decreases demand charges
Correct answer: It increases current draw for the same real power, increasing conductor losses
A low power factor means more current is required to deliver the same real power (watts), increasing IĀ²R losses and potentially requiring larger conductors.
Question 2: Which type of overcurrent protective device provides both overload and short-circuit protection and is commonly used in motor branch circuit applications?
- Thermal-magnetic circuit breaker
- Current-limiting fuse only
- Dual-element time-delay fuse (Correct answer)
- Instantaneous-trip breaker
Correct answer: Dual-element time-delay fuse
A dual-element time-delay fuse provides motor overload protection through its thermal element and short-circuit protection through its current-limiting element.
Question 3: In a switchgear lineup, what is the function of a bus tie breaker?
- To connect a generator to the utility bus
- To allow two bus sections to be electrically connected or isolated (Correct answer)
- To provide ground fault protection for the entire bus
- To limit fault current from one feeder to another
Correct answer: To allow two bus sections to be electrically connected or isolated
A bus tie breaker connects two separate bus sections, allowing either section to supply loads normally fed by the other in case of a source failure.
Question 4: What is the purpose of a surge protective device (SPD) Type 1 installed at the service entrance?
- To regulate voltage sags caused by motor starting
- To divert lightning-induced surges and externally generated transients before they enter the building wiring (Correct answer)
- To filter harmonic distortion from variable frequency drives
- To correct power factor automatically
Correct answer: To divert lightning-induced surges and externally generated transients before they enter the building wiring
A Type 1 SPD is rated for installation at the service entrance and is designed to handle surge energy from external sources such as direct lightning strikes to the service.
Question 5: An automatic transfer switch (ATS) switches a load from normal utility power to a generator. The ATS monitors utility voltage and frequency; it transfers when utility voltage drops below what typical threshold?
- 50% of nominal
- 70% of nominal
- 80% of nominal (Correct answer)
- 95% of nominal
Correct answer: 80% of nominal
Most ATS units are factory-set to initiate generator startup and transfer when utility voltage drops below approximately 80% of nominal voltage.
Question 6: In a radial distribution system, what is the primary disadvantage compared to a loop or ring bus arrangement?
- Higher initial equipment cost
- A single fault on the feeder can cause a complete loss of power to all downstream loads (Correct answer)
- More complex protection coordination required
- Greater voltage rise at the end of the feeder
Correct answer: A single fault on the feeder can cause a complete loss of power to all downstream loads
A radial system has no redundancy; if the single feeder supplying a section faults, all loads on that section lose power until the fault is cleared.
CEP CEP Power Systems & Distribution 2
What is the effect of a low power factor on an electrical distribution system?