Engineering Transmission Distribution interview prep.

Transmission planners, distribution planners, substation engineers, protection + control engineers, line design, asset managers at vertically-integrated utilities + T&D utilities + ISOs / RTOs.

What interviewers look for

  • Can the candidate apply NERC TPL planning discipline - contingency studies, IROL / SOL identification, corrective action?
  • Do they understand substation + line design - one-lines, BIL, NESC clearances, sag-tension, structural load cases?
  • Are they fluent in protection coordination - distance, differential, overcurrent, breaker-failure, misoperation review?
  • Can they reason about distribution planning - load forecasting, DER hosting capacity, reliability indices, storm hardening?
  • Do they navigate interconnection studies (generation + load) per FERC LGIA + IEEE 1547?
  • Are they comfortable with rate-case + IRP + regulator justification of capital projects?
  • Long-game fit - engineer / senior / principal / engineering manager / chief engineer trajectory?

Behavioural questions to expect

  1. Walk me through your background + T&D engineering experience.

    What it tests: Story arc - power-systems training + design / planning anchors + standards exposure.

  2. Tell me about a transmission or distribution project you've led.

    What it tests: Project + standards thinking + cross-discipline integration + outcome.

  3. Why T&D engineering vs other power-systems paths (generation, grid ops, protection R&D)?

    What it tests: Authentic alignment - planning + design + asset stewardship + multi-decade thinking.

  4. Why this discipline - transmission planning, substation, line, protection + control, distribution planning?

    What it tests: Specificity. Generic answers fail. Substation design + transmission planning + P&C are markedly different daily work.

  5. Why this firm?

    What it tests: Real homework - footprint + capital plan + reliability posture + culture - not name-drop.

  6. What's your read on our T&D capital plan + recent rate case or IRP?

    What it tests: Industry literacy - capital programme, regulator posture, recent events, reliability trend.

  7. Tell me what you understand about our NERC compliance + reliability posture.

    What it tests: Reliability + compliance fluency on this firm's standards posture + reliability indices.

  8. Walk me through a transmission planning or interconnection study you've done.

    What it tests: TPL / FAC / interconnection fluency - power-flow, contingency, voltage / stability, mitigation options.

Technical concepts to master

Transmission planning + interconnection studies

Power-flow + N-1 contingency analysis
AC power-flow under base + contingency cases against thermal + voltage limits per TPL-001.
Short-circuit + fault duty
Calculates fault currents to size breakers + verify equipment ratings per ANSI C37.
Transient + voltage stability
Simulates dynamic response to faults + large disturbances; checks angle + voltage recovery.
LGIA + Cluster Study (FERC Order 2023)
Standard interconnection process - feasibility, system impact, facilities study - cluster-based per Order 2023.

Substation + transmission line design

Bus configurations
Single, main + transfer, ring, breaker-and-a-half, double-breaker - trade reliability vs cost + footprint.
BIL + insulation coordination
Basic Insulation Level - withstand voltage standard for lightning + switching surges.
NESC clearances + structural loading
Minimum clearances to ground + obstacles + between conductors; structural loads (ice + wind + dead).
Sag-tension + dynamic line rating
Conductor sag + tension vs temperature + ice + wind; ampacity per IEEE 738.

Protection + control coordination

Distance (impedance) protection
Multi-zone impedance-based protection for transmission lines - Zone 1 (instant), Zone 2 (delayed), Zone 3 (backup).
Differential protection
Compares current entering vs leaving zone - high-speed unit protection for buses, transformers, lines.
Overcurrent + coordination
Time + instantaneous overcurrent with inverse-time curves - distribution + backup transmission.
Breaker-failure + redundancy
Backup scheme initiating zone trips if primary breaker fails; redundant primary + backup relays.

Distribution planning + DER hosting + reliability

Load forecasting + feeder loading
Spatial + temporal forecast of loads by feeder + substation; thermal + voltage limits drive upgrades.
DER hosting capacity
Maximum DER MW a feeder can accommodate without exceeding voltage / thermal / protection limits.
Reliability indices + drivers
SAIDI / SAIFI / MAIFI / CAIDI per IEEE 1366; drivers - vegetation, equipment, animals, weather.
Storm hardening + undergrounding
Hardening investments - undergrounding, stronger poles, vegetation, sectionalising, microgrids.

Practical drills

  • A 500 MW solar farm requests interconnection at a 230 kV substation 40 miles from your load centre. The local 230 kV system is rated 1,400 MW thermal. Walk through your interconnection study + mitigation plan.
  • A new 138 kV line ties into an existing substation. Walk through your protection design + coordination approach + commissioning.
  • A 12.47 kV feeder has SAIDI 180 min (vs system 110) + growing rooftop solar approaching 30% of feeder peak. Walk through your reliability + DER plan for this feeder.

Smart-question anchors

  • T&D capital plan + IRP - signature programmes, grid mod, undergrounding
  • Reliability indices + drivers - SAIDI / SAIFI / MAIFI trend + storm hardening
  • NERC compliance - TPL / FAC / PRC audit posture + Regional Entity
  • Interconnection queue + DER hosting - process + recent volumes
  • Engineering org + tool stack - PSS/E / CYME / ASPEN / Synergi + planning / substation / line / P&C groups

Related roles

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