PECO Distribution Systems & Infrastructure 2 — Questions and Answers
Question 1: Which type of cable insulation is most commonly used in PECO's underground distribution system for medium-voltage circuits?
- Oil-impregnated paper (PILC)
- Cross-linked polyethylene (XLPE) (Correct answer)
- Rubber (natural)
- Polyvinyl chloride (PVC)
Correct answer: Cross-linked polyethylene (XLPE)
Cross-linked polyethylene (XLPE) is the predominant insulation for modern medium-voltage underground distribution cables due to its superior thermal and electrical properties.
Question 2: What does the acronym 'URD' stand for in the context of PECO distribution infrastructure?
- Utility Reliability Division
- Underground Residential Distribution (Correct answer)
- Uniform Relay Diagram
- Unit Restoration Dispatch
Correct answer: Underground Residential Distribution
URD stands for Underground Residential Distribution, referring to the system of underground cables and pad-mounted transformers that serve residential subdivisions.
Question 3: A PECO feeder circuit experiences a permanent three-phase fault. Which protection device at the substation is the first to respond?
- Distribution transformer fuse
- Substation feeder breaker (Correct answer)
- Line recloser
- Sectionalizer
Correct answer: Substation feeder breaker
The substation feeder breaker is the first-line protection device and will trip on a permanent three-phase fault at the substation level before downstream devices operate.
Question 4: What is the main advantage of a looped (ring-bus) distribution system over a radial distribution system for PECO's service area?
- Lower capital installation cost
- Improved supply reliability through alternate feed capability (Correct answer)
- Elimination of transformer losses
- Reduced need for protective relaying
Correct answer: Improved supply reliability through alternate feed capability
A looped or ring-bus distribution system allows power to be rerouted from an alternate feed point during a fault or maintenance, improving service reliability compared to a radial system.
Question 5: PECO installs capacitor banks on distribution feeders primarily to accomplish which of the following?
- Increase fault current for faster relay operation
- Provide reactive power compensation and improve power factor (Correct answer)
- Limit harmonic distortion from customer loads
- Step up voltage for long-distance transmission
Correct answer: Provide reactive power compensation and improve power factor
Capacitor banks supply reactive power (VARs) locally on the feeder, improving power factor, reducing I²R losses, and helping maintain acceptable voltage levels.
Question 6: In the context of PECO distribution operations, what is a 'pad-mounted transformer'?
- An overhead transformer mounted on a wooden pole
- A ground-level, tamper-resistant transformer in a locked enclosure set on a concrete pad (Correct answer)
- A substation power transformer on vibration-dampening pads
- A portable transformer used during outage restoration
Correct answer: A ground-level, tamper-resistant transformer in a locked enclosure set on a concrete pad
A pad-mounted transformer is a ground-level distribution transformer housed in a locked, tamper-resistant metal enclosure bolted to a concrete pad, commonly used in URD systems.
Question 7: Which conductor configuration is most commonly used for PECO overhead distribution primary lines to reduce line losses and improve voltage regulation?
- Single-wire earth return (SWER)
- Balanced three-phase three-wire or four-wire configuration (Correct answer)
- Two-wire single-phase configuration only
- Bundled conductor with four sub-conductors per phase
Correct answer: Balanced three-phase three-wire or four-wire configuration
PECO overhead primary distribution lines are predominantly configured as balanced three-phase three-wire or four-wire (with neutral) circuits to efficiently distribute power with minimized losses.
PECO Distribution Systems & Infrastructure 2
Which type of cable insulation is most commonly used in PECO's underground distribution system for medium-voltage circuits?