Substation Technician Interview Questions
30 questions
Question 1: Walk me through how you track down a fault in a control circuit using the wiring diagrams and a meter.
Suggested answerThe interviewer wants to see that you troubleshoot with a method, not by guesswork, and that you work safely around energized circuits.
Structure the answer as a sequence. Start with how you gather information: the symptom, alarms or targets, and the right schematic and wiring diagram. Then explain how you make the work safe, such as confirming which circuits are live and following your company's clearance rules. Next, describe how you test: tracing the circuit on the print, taking voltage readings across contacts and coils, and checking continuity with the circuit de-energized. Finish with how you confirmed the fix and updated records.
Sample answer: "A breaker wouldn't close from the control house. I pulled the elementary diagram and traced the close circuit. I had DC at the control switch but not at the close coil, so I worked down the circuit taking readings across each contact. A cutoff switch contact in the breaker cabinet was open when it should have been closed. After we cleared the breaker, I adjusted the linkage, tested the close and trip operations, and noted the repair in the maintenance log."
Pitfalls to avoid: skipping the safety steps, describing parts swapped at random, and leaving out how you proved the fix worked.
What interviewers listen forLook for a logical method: check the prints, confirm the circuit is safe, then test point by point with a voltmeter or ohmmeter. Guessing and swapping parts is a red flag.
Candidate tipUse one real example. Describe how you read the schematic, which meter readings you took and in what order, and how you confirmed the fix.
Question 2: Describe how you check out a new or rebuilt substation relay and control panel before it goes into service.
Suggested answerThe interviewer wants to know you can commission protection and control equipment thoroughly, so it trips when it should and only then.
Walk through your process in order. Typical steps include checking the wiring point to point against the drawings, confirming CT and PT circuits, loading and verifying the approved relay settings, testing each relay with a test set, and doing functional trip and close checks all the way to the breaker. Mention who you work with, such as the protection engineer and system operators, and how you document results.
Sample answer: "On a recent panel replacement, I started by checking the wiring against the schematics and marking each point on a print. I verified the CT circuits for polarity and grounding. I loaded the settings file the engineer issued and confirmed it on the relay screen. Then I tested each protective element with a test set and compared the results to the settings. Last, we did trip checks to the breaker and alarm checks to the control center. I filed the test reports before we put it in service."
Pitfalls to avoid: skipping functional trip tests, using settings that weren't approved, and forgetting the paperwork.
What interviewers listen forStrong answers cover point-to-point wiring checks, relay testing with a test set, trip checks to the breaker and a review with the protection engineer. Skipping a trip test is a red flag.
Candidate tipWalk through your steps in order, from wiring checks and relay testing to functional trip tests, and say how you documented the results.
Question 3: What would you do if a protective relay needed repair but you could not confirm which switches would isolate it?
What interviewers listen forThey should stop and resolve the isolation plan with the system operator using current drawings and switching instructions. Operating switches by guesswork is an unsafe first move.
Candidate tipStart with what you would hold off on until the relay isolation is confirmed. Name the drawings, switching instructions, and person you would consult before work could proceed.
Question 4: What is the most challenging part of analyzing test data in order to diagnose malfunctions, to determine performance characteristics of systems, and to evaluate effects of system modifications?
Question 5: How often do you find yourself consulting manuals, schematics, wiring diagrams, and engineering personnel in order to troubleshoot and solve equipment problems and to determine optimum equipment functioning? Share an example.
Question 6: How often do you need to prepare and maintain records detailing tests, repairs, and maintenance? Why is it important?
Question 7: Tell me about a time you found and fixed a protective relay that was misoperating or out of calibration.
Suggested answerThe interviewer wants to see how you diagnose a relay problem, fix it within your authority and prove the repair.
Use Situation, Task, Action, Result. Describe the relay and what went wrong, such as a trip that shouldn't have happened or a test result outside tolerance. Explain how you confirmed the problem with a test set and the settings record, what you changed or replaced, and how you retested it. Close with the outcome and what you documented.
Sample answer: "During routine testing, an overcurrent relay on a feeder was picking up well above its setting. I checked the settings record to be sure I was testing against the right values, then repeated the test to rule out my test leads. The result held, so with the engineer's okay I recalibrated the relay to the manufacturer's procedure. I retested pickup and timing at several points, and everything was within tolerance. I recorded the as-found and as-left values so the trend would show if it drifted again."
Pitfalls to avoid: changing settings without approval, leaving out the as-found and as-left records, and claiming a fix without a final test.
What interviewers listen forListen for how they confirmed the problem with a test set and the settings record before adjusting, and how they proved it afterward. Changing settings without approval is a red flag.
Candidate tipName the relay type and the symptom, then walk through how you isolated it, tested it against the settings sheet, made the fix and proved it with a final test.
Question 8: Tell me about a time your attention to detail caught an error in relay settings or wiring before it caused a problem.
Suggested answerThe interviewer wants proof that you check your work and others' carefully, because a small error in protection can cause a misoperation or an outage.
Use Situation, Task, Action, Result. Set the scene, say what you were checking, describe the error you found and how you confirmed it, then explain what was corrected and what could have happened otherwise.
Sample answer: "Before energizing a new transformer, I was comparing the relay settings file to the one-line diagram. The CT ratio entered in the differential relay didn't match the CTs shown on the drawing. I checked the nameplates in the field to be sure which was right, and the drawing was correct. I sent it to the protection engineer, who issued a corrected file, and I retested the relay with the new settings. If we'd energized with the wrong ratio, the relay could have tripped the transformer on normal load."
Pitfalls to avoid: choosing an example with no real consequence, taking credit for catching something without saying how you confirmed it, and suggesting you fixed settings on your own without approval.
What interviewers listen forListen for how they check settings files, drawings and test results against each other; a strong answer names the error and its likely effect. Relying on memory instead of checking is a red flag.
Candidate tipDescribe what you were checking, the error you found, how you confirmed it, and what could have happened if it had been missed.
Question 9: Share an example of how you kept facility personnel informed when the timing of an equipment shutdown changed during a substation repair.
What interviewers listen forA strong example names who needed the revised shutdown notice, how they received it, and the result. Assuming an earlier notice still covered the new timing is a warning sign.
Candidate tipChoose one shutdown whose timing changed. Explain your part in updating facility personnel, how you checked that the message reached them, and what happened.
Question 10: Tell me about a time a substation inspection helped you catch a problem before it caused an outage.
Suggested answerThe interviewer wants to know you inspect with care and act on what you find, rather than just walking through.
Use Situation, Task, Action, Result. Say what kind of inspection it was, what you noticed, how you confirmed the cause, and how it was fixed. Mention how you reported and recorded it.
Sample answer: "On a monthly substation walkdown, I noticed the oil level gauge on a breaker was lower than on the last inspection, and there was a small stain on the pad. I checked the inspection records and saw the level had been dropping slowly. I reported it to my supervisor and wrote it up so the breaker could be scheduled for an outage. When we opened it, a gasket was leaking. We replaced the gasket, topped up the oil, and tested the oil before returning it to service. Catching it early meant we fixed it on our schedule instead of during a failure."
Pitfalls to avoid: describing a problem someone else found, leaving out how you confirmed the cause, and forgetting to say how you documented and reported it.
What interviewers listen forLook for what they noticed (heat, noise, an oil leak, alarms or odd readings) and how they followed up and reported it. Finding a problem and not documenting it is a red flag.
Candidate tipDescribe what you saw or measured on the walkdown, how you confirmed the cause, and what was done to fix it before it failed.
Question 11: Walk me through how you decided when and what maintenance a circuit breaker or transformer needed on your last routine maintenance job.
Suggested answerThe interviewer wants to learn how you use a circuit breaker's or transformer's maintenance history and condition to decide the timing and scope of routine work.
Use Situation, Task, Action, Result to organize your last routine maintenance job. Briefly name the equipment and the maintenance need. Explain your responsibility, then focus on how you used the schedule, earlier test results and manufacturer guidance to choose the work. Finish with the outcome and anything you learned that would help with the next maintenance decision.
For example: "On my last circuit breaker maintenance job, the schedule showed that service was due. I reviewed the previous inspection notes and test results against the manufacturer's guidance. The notes described slow operation, so I included a closer check of the operating mechanism in the planned work. After maintenance, the operating check met the specified limits. I recorded the work and results. That job reminded me to read the inspection notes as well as the test sheet."
Avoid listing maintenance steps without explaining your choices. Don't claim a schedule alone proves the equipment is in good condition, or overlook earlier results that need attention.
What interviewers listen forThe example should connect the maintenance schedule, past test results and manufacturer guidance to their choices. Ignoring a test result that calls for attention is a red flag; ask about the outcome and lessons.
Candidate tipPick your last routine breaker or transformer maintenance job. Show how the schedule, earlier test results and manufacturer guidance shaped your decisions, then give the result and what you learned.
Question 12: Walk me through a repair you made after finding worn brushes or commutator damage in generating-station equipment.
What interviewers listen forListen for their own repair steps, checks before return to service, and the result. Replacing brushes without checking the commutator's condition can leave the cause unresolved.
Candidate tipUse one brush or commutator repair. Briefly describe the wear or damage, then focus on your repair, how you checked the equipment afterward, and what you learned.
Question 13: How do you check both signal quality and connectivity on a substation cable for a test report?
What interviewers listen forExpect tests suited to the cable and signal, comparison with specified limits, and results tied to the cable's identity. A continuity pass alone does not establish signal quality.
Candidate tipName the cable and signal type, then walk through your test setup, the limits you compare against, and what you enter in the cable test report.
Question 14: Tell me about a time you went beyond your normal duties to get a substation or generating unit back in service safely.
Suggested answerThe interviewer wants to know you can be counted on when equipment fails, and that you stay safe and within procedure when there's pressure to restore power.
Use Situation, Task, Action, Result. Describe the outage or callout, what was at stake, what you did that went beyond your usual role, and how you kept the work safe. End with the result.
Sample answer: "A storm tripped a transformer at one of our substations late at night, and I was on call. The relay targets pointed to a fault outside the transformer, but I wanted to be sure before re-energizing. I stayed past my shift to help the operator review the event record and walked the bus with a second tech to look for damage. We found a damaged arrester and isolated it under a proper clearance. Once the engineer reviewed the data, the transformer went back in service and the arrester was replaced the next day."
Pitfalls to avoid: suggesting you bypassed clearance or safety rules to finish faster, making it sound like you worked alone without the operator, and leaving out the outcome.
What interviewers listen forA strong answer shows reliability under pressure while still following clearance and safety rules. Cutting safety corners to finish faster is a red flag.
Candidate tipPick a real outage or callout, explain what was at stake, what you did beyond your usual role, and how you kept the work safe.
Question 15: How do you plan and prioritize your work when several maintenance jobs need the same outage window?
What interviewers listen forLook for planning around the outage schedule and system risk, with parts and test equipment ready ahead of time. Leaving preparation until the outage starts is a red flag.
Candidate tipExplain how you rank jobs by risk and deadline, coordinate the outage with operations, and prepare tools, parts and paperwork beforehand.
Question 16: Tell me about a time you had to learn a new relay test set or a new type of digital relay quickly.
Suggested answerThe interviewer wants to see how you learn new equipment, and that you get competent with it before relying on it for live work.
Use Situation, Task, Action, Result. Say what the equipment was and why you had to learn it quickly. Explain how you learned it, such as manuals, training, help from experienced techs or bench practice. Finish with how you used it on the job and what you'd do the same way next time.
Sample answer: "Our shop replaced its older relay test sets with a new model a week before a busy outage season. I read the manual, went through the vendor's online training, and then practiced on a spare relay on the bench until I could build and run test plans without help. I made a short checklist for the setup steps. During the outages I used it on several feeder relays, and I shared the checklist with two coworkers who were still learning it."
Pitfalls to avoid: saying you figured it out on energized equipment, leaving out how you checked your own competence, and naming no result.
What interviewers listen forA strong answer shows they used manuals, training or a senior tech, then practiced on the bench before live work. Learning by trial and error on in-service equipment is a red flag.
Candidate tipSay what the equipment was, how you learned it (manual, training, bench practice), and how you showed you could use it safely on the job.
Question 17: Tell me about a time you helped bring new technology into your work, such as replacing electromechanical relays with microprocessor relays.
What interviewers listen forListen for how they learned the new equipment, adapted test procedures and helped others; a strong answer names a concrete benefit. Resisting the change with no reason is a red flag.
Candidate tipName the technology, what you did to learn and apply it, and what improved, such as faster testing or better fault records.
Question 18: Describe a time you corrected a mismatch between the spare-parts inventory record and the substation parts actually on hand.
What interviewers listen forThe example should show how they checked part identities and counts, corrected the record, and addressed any shortage. Changing a count without verifying the stock leaves the mismatch unresolved.
Candidate tipPick one inventory mismatch. Describe your count and part-number checks, the record correction, any replacement request needed, and the result for the spare-parts supply.
Question 19: Walk me through how you test insulators and bushings of equipment by inducing voltage across insulation, testing current, and calculating insulation loss.
Question 20: Share an experience in which you conducted a test of a product, service, or process and successfully improved the quality or performance.
Suggested answerThe interviewer wants evidence that you test things carefully and use what you find to make them better.
Use Situation, Task, Action, Result. Explain what you tested and why, how you set up the test, what the results showed, and what you changed. End with how you measured the improvement.
Sample answer: "Customers kept saying our online order form was confusing, so I was asked to look into it. I had five coworkers who had never used the form place a test order while I watched and took notes. Four of them got stuck on the same shipping step. I suggested moving that step and rewording two labels, then ran the same test again. All five finished without help, and complaints about the form dropped over the next month."
Pitfalls: Don't describe a change made on a hunch with no test. Avoid skipping how you checked the result. Don't use jargon without explaining it.
Question 21: What kind of experience do you have disconnecting voltage regulators, bolts, and screws, and connect replacement regulators to high-voltage lines? Share an experience.
Question 22: Share an example of how you explained the prints to a crew you led in building or modifying a relay or control panel.
What interviewers listen forListen for their own explanation of the prints, checks of the crew's understanding, and the result. Guessing at unclear wiring details is a red flag; ask what they learned about giving instructions.
Candidate tipUse a real relay or control panel job. Describe how you explained the prints and any changes to the crew, how you checked their understanding, and what the finished work taught you about your instructions.
Question 23: Tell me how you handled a disagreement with a system operator, contractor or crew member during an outage.
What interviewers listen forA strong example shows how they resolved the disagreement while respecting the switching order and clearance. Going around the operator to get work done is a red flag; listen for the result and what they learned.
Candidate tipChoose one outage disagreement. Explain your part in resolving it, how you kept the switching order and clearance intact, and what the outcome taught you about working with the operator or crew.
Question 24: Provide a time when you dealt calmly and effectively with a high-stress situation.
Suggested answerThe interviewer wants to see how you think and act under pressure, and whether you stay effective when things go wrong.
Use Situation, Task, Action, Result. Set the scene quickly: what made it stressful and what was at stake. Spend most of your answer on what you did: how you steadied yourself, what you dealt with first, and who you told. Close with the outcome and what you would repeat.
Sample answer: "An hour before a client presentation, the file with our final numbers was corrupted. I told the team we had a problem and a plan, split the work so two of us rebuilt the charts from the source data while another person checked them, and let the client know we might start a few minutes late. We started on time, and afterward we set up automatic backups for shared files."
Pitfalls: Don't say you never feel stress. Avoid stories where the stress came from your own avoidable mistake unless you explain what you changed. Don't skip the result.
Question 25: Provide an example when your ethics were tested.
Suggested answerThe interviewer wants to know whether you do the right thing when it is inconvenient, and how you handle pressure to cut corners.
Use Situation, Task, Action, Result. Describe the pressure or temptation without naming people, explain the choice you made and why, and how you handled the conversation. Keep the focus on your actions, not on judging others.
Sample answer: "Near the end of a quarter, a coworker asked me to record a sale as complete even though the customer hadn't signed yet, so our numbers would look better. I told them I wasn't comfortable doing that and suggested we tell our manager the deal would close the following week. My manager agreed it should wait. The customer signed early in the new quarter, and our records stayed accurate."
Pitfalls: Don't say your ethics have never been tested. Avoid stories that make you sound self-righteous or that share confidential details. Don't pick an example where you went along with the wrong choice and stop there.
Question 26: Tell me about your last experience doing repair work. How did you determine what tools you needed?
Suggested answerThe interviewer wants to see how you plan a repair, including choosing the right tools, so the job is done safely and well.
Use Situation, Task, Action, Result. Describe the repair, how you figured out what was wrong, how you decided on tools and parts (the manual, the fasteners involved, what you saw during inspection), and how the repair turned out.
Sample answer: "A door closer at our building's entrance was letting the door slam. I checked the manual for that model and learned the speed valves needed a small hex key, and that a leaking closer would need replacing instead. I looked for oil around the body, saw none, and brought the hex key, a step ladder, and a rag. I adjusted the closing and latch speeds a little at a time and tested the door after each turn. It closed smoothly, and I noted the settings in our maintenance log."
Pitfalls: Don't describe grabbing whatever tool was nearby. Avoid skipping how you tested the repair. Don't forget to answer the tools part of the question.
Question 27: Provide an example of a time when you were able to demonstrate excellent listening skills. What was the situation and outcome?
Suggested answerThe interviewer wants evidence that you listen to understand, not just to reply, and that it makes a difference to your work.
Use Situation, Task, Action, Result. Show what careful listening looked like: letting the person finish, asking follow-up questions, and repeating back what you heard. The outcome should show that listening caught something you would otherwise have missed.
Sample answer: "A manager from another department asked for a monthly report and said they wanted it faster. Instead of starting right away, I asked what they used the report for. They mentioned twice that they only looked at two of the columns. I confirmed that with them, built a one-page summary of just those figures, and it took a third of the time to produce. They used the summary format from then on."
Pitfalls: Don't just describe yourself as a good listener without an example. Avoid an answer where you talk mostly about what you said. Don't leave out the outcome the question asks for.
Question 28: Share an experience in which you successfully coordinated with others. How about a coordination effort that was not as successful?
Suggested answerThe interviewer wants to see how you work with others to line up schedules, tasks, and handoffs, and whether you learn from times it didn't work.
The question asks for two stories, so keep each one short. For the success, explain who was involved, how you kept everyone in step, and the result. For the less successful one, say what went wrong, your part in it, and what you now do differently.
Sample answer: "For an office move, I set up a shared timeline with the facilities, technology, and department leads, and held a 15-minute check-in each week. Everyone was set up and working by Monday morning. Earlier, on a smaller project, I assumed a vendor knew our deadline and didn't confirm it. Their delivery came two days late. Since then I confirm key dates in writing with everyone involved."
Pitfalls: Don't spend all your time on the success. Avoid blaming others for the one that went wrong. Don't skip what you learned.
Question 29: Describe an experience in which you successfully controlled the operation of a difficult system. What made you successful?
Suggested answerThe interviewer wants to see that you can run complex equipment or processes safely and stay in control when things get hard.
Use Situation, Task, Action, Result. Describe the system and what made it difficult, how you monitored it, the adjustments you made, and what made you successful, such as training, checklists, or close attention.
Sample answer: "I ran a packaging line that often jammed when we switched to a thinner film. Before each changeover, I followed the setup checklist, then ran a few slow test cycles while watching the sensors. When a jam started to build, I lowered the speed and adjusted the tension in small steps instead of stopping the whole line. Our changeover downtime went down over the next few weeks, and I added my steps to the shift notes so others could use them. Patience and sticking to the procedure made the difference."
Pitfalls: Don't skip safety steps in your story. Avoid technical detail the interviewer can't follow. Don't leave out what made you successful, since the question asks.
Question 30: Provide an experience that demonstrates your ability to manage time effectively. What were the challenges and results?
Suggested answerThe interviewer wants to know how you plan your time and handle competing demands, and whether you meet deadlines.
Use Situation, Task, Action, Result. Name the specific challenges, such as overlapping deadlines or interruptions. Describe the steps you took to plan and protect your time, and what you did when something came up. End with the results the question asks for.
Sample answer: "During one busy week, I had a report due Thursday, two new team members to train, and my usual daily tasks. I mapped out the week on Monday, scheduled training for the mornings when things were quieter, and blocked two afternoons for the report. When an urgent request came in Wednesday, I asked a colleague to cover one training session. The report went in a day early, and both new team members finished their training on schedule."
Pitfalls: Don't just list time-management tools. Avoid a story where you met the deadline only by working through the night. Don't skip the challenges.