TUNNEL

Question 1

Experience with Medium-Voltage Power Distribution

Answer 1

Situation: At Pepco (Exelon), I was responsible for improving reliability across underground and overhead distribution feeders ranging from 4kV–34.5kV.
Task: I needed to understand and document system topology, evaluate equipment loading, and support safe reconfiguration of feeders during switching and maintenance.
Action: I routinely reviewed and updated single line diagrams, verified transformer and cable ratings, analyzed feeder load flow, and collaborated with substation engineering on breaker protection coordination. I also used GIS, SCADA, and relay setting data to confirm switchgear configurations and validate field conditions.
Result: My work improved the accuracy of system documentation, reduced switching errors, and supported reliability improvements that directly contributed to better SAIDI/SAIFI performance. It also prepared me to manage plant-level distribution assets similar to those at Tunnel 9, including transformers, switchgear, MCCs, and substations.

Question 2

Troubleshooting Power System Failures Under Time Pressure

Answer 2

Situation: During my reliability role at Pepco, I was assigned to investigate repeated outages on a critical URD loop affecting a high-priority customer.
Task: The goal was to identify the true root cause quickly, recommend corrective actions, and support the field team in restoring service.
Action: I analyzed SCADA event logs, reviewed protection operations, and compared them to load-flow and fault-current models. During the next outage event, I coordinated with field engineering to isolate segments and used feeder analytics to pinpoint a failing cable section that intermittently faulted under load. I helped direct the switching operations and verified relay coordination settings after repairs.
Result: The issue was fixed within the same shift, customer reliability was restored, and the circuit’s momentary and sustained outages dropped for the remainder of the year. This experience translates directly to Tunnel 9’s requirement to respond quickly during tests, diagnose a malfunction, and safely return high-energy systems to service.

Question 3

Creating or Checking Electrical Drawings (SLDs, Schematics, CAD)

Answer 3

Situation: As a Reliability Engineer, I frequently found inconsistencies between field conditions and legacy feeder documentation.
Task: I needed to ensure accurate SLDs and asset documentation for safe switching, planning studies, and regulatory compliance.
Action: I interpreted and corrected SLDs, verified conductor and transformer ratings, checked tie and sectionalizing points, and validated relay settings against actual equipment. I also reviewed as-built drawings from capital projects and coordinated with field crews to reconcile discrepancies.
Result: These corrections reduced system configuration errors, improved operational readiness, and streamlined the approval process for feeder reconfiguration and maintenance. This background directly supports Tunnel 9’s requirement to generate or check electrical drawings, equipment layouts, and wiring diagrams with high accurac

Question 4

Fault Current or Voltage Drop Analysis

Answer 4

Situation: At Pepco, I supported distribution planning by evaluating both steady-state and fault characteristics of feeders during upgrades and reconfiguration studies.
Task: I needed to ensure feeders operated within equipment ratings, maintained proper voltage balance, and had protection coordination aligned with NERC and company standards.
Action: I performed short-circuit calculations, reviewed breaker and relay protection curves, and evaluated cable and transformer loading limits. For voltage drop, I modeled various feeder configurations using GIS/SCADA data and engineering tools to check compliance with voltage criteria under both normal and contingency loading.
Result: My analyses confirmed that proposed feeder configurations were safe, electrically stable, and adequately protected. This directly prepares me for Tunnel 9’s requirement to lead fault current, voltage drop, and reliability studies for high-energy test systems.

Question 5

NEC / IEEE Standards Compliance in Design Work

Answer 5

Situation: Many of Pepco’s feeders required upgrades driven by NEC requirements, IEEE protection standards, and energy balance metrics.
Task: I needed to ensure my reliability assessments and recommendations complied with NEC ampacity, grounding, arc-flash, and protection standards.
Action: I referenced NEC tables for conductor sizing and temperature ratings, verified grounding/bonding requirements, and evaluated equipment spacing and clearance criteria. I aligned protection coordination with IEEE standards (including IEEE 1584 for arc-flash and IEEE C37 series for protective devices).
Result: This ensured that new switching schemes, transformer upgrades, and cable replacements met design and safety requirements and passed internal engineering review. My experience applying NEC and IEEE standards directly aligns with Tunnel 9’s requirement for code-compliant system design and documentation.

Question 6

Leading an Engineering Upgrade or Improvement Project (Planning → Execution)

Answer 6

Situation: Pepco initiated a series of reliability improvement projects targeting aging URD infrastructure with high outage counts.
Task: I was responsible for scoping, prioritizing, and supporting execution of upgrades on underperforming feeders.
Action: I performed risk-based assessments, reviewed asset health reports, validated as-builts, and identified root causes such as cable degradation, miscoordination, or transformer overloads. I wrote technical findings, supported budget justification, coordinated with planning, and worked with field crews to verify proper implementation.
Result: These projects reduced outage frequency and duration on targeted circuits, improved reliability indices, and validated the engineering plan for capital expenditures. This directly aligns with Tunnel 9’s requirement to plan, budget, schedule, design, coordinate contractors, and execute electrical system upgrades.

Question 7

SAIDI

Answer 7

SAIDI

System Average Interruption Duration Index

What it measures:
The average outage duration experienced by each customer over a given period (usually a year).

Formula:

Total customer interruption minutes/Total customers served
​

Plain English:
“How many minutes of outage the average customer experienced.”

Question 8

SAIFI

Answer 8

SAIFI

System Average Interruption Frequency Index

What it measures:
The average number of outages per customer over a given period.

Formula:

Total customer interruptions/Total customers served

​ Plain English: “How many times the average customer lost power.”

Question 9

CAIDI

Answer 9

CAIDI

Customer Average Interruption Duration Index

What it measures:
The average time required to restore service after an outage.

Formula:

SAIDI/SAIFI

​

Plain English:
“How long it takes on average to restore power once a customer goes out.”