Back-Feed from a Consumer Generator During a Feeder Shutdown
An 11 kV feeder is switched off at the 33/11 kV substation for replacement of a damaged pole. The substation issues a permit-to-work and applies a visible earth at the feeder isolator. The line crew travels 4 km to the work site. At the site, the lineman checks the conductor with a low-voltage detector, finds no voltage, and starts work without applying portable earths at the work location. A nearby cold-storage consumer has a 125 kVA diesel generator connected to its LT busbar through a manual changeover switch. The changeover is not interlocked, and the consumer's staff start the generator because of a power cut. The generator back-feeds the consumer's 11/0.4 kV transformer. A lineman on the pole receives an electric shock from the supposedly dead 11 kV conductor and falls onto the roadside. The pole has no fall-arrest lanyard in use.
1. Identify the sequence of failures that made the conductor live, and explain why the substation earth alone did not protect the crew.
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The conductor became live because the consumer's 125 kVA generator back-fed the LT busbar and the 11/0.4 kV transformer stepped the voltage up to 11 kV. The manual changeover had no interlock, and either it was closed to the generator while the transformer remained connected or the interlock was bypassed; the consumer was not isolated or warned. The crew then made two serious errors: they used a low-voltage detector, which is not suitable for proving an 11 kV conductor dead, and they did not apply portable earths at the work site. The substation earth protects the section between the substation and its earth point, but it does not bond the remote work site. The work site therefore remained at a dangerous potential. The missing fall-arrest lanyard turned an electrical incident into a fall incident. The permit system failed because it did not identify the generator as a potential source or require site earthing.
2. State the immediate rescue and first-aid actions, including what must not be done.
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Do not touch the victim or the conductor. Shout for help and call the emergency number. Isolate the generator and the 11 kV feeder; if the victim is still in contact, use an insulated rescue device from a safe position. Once clear, check responsiveness, breathing and pulse. Start CPR if breathing is absent and use an AED as soon as available. Treat burns and shock, keep the victim warm, and suspect spinal injury after the fall; do not move the victim unless there is immediate danger. Do not climb the pole without fall protection, and do not re-energize the line. Hand over all information to the ambulance team and record the times of isolation, CPR and recovery.
3. What should be corrected in the permit, earthing and consumer-interface procedure before the feeder is restored?
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Before restoration, revise the permit to list every source, including generator, solar and UPS back-feed. Apply lockout/tagout at the substation and at the consumer's changeover, and issue a written notice to the consumer. At the work site, prove dead with a properly rated detector and apply portable earths on both sides of the work point. Use an interlocked changeover or, better, a generator that cannot parallel with the network. Require a safety briefing and fall-arrest use for all pole work. After the incident, inspect and test the line, remove all earths in the correct order, and cancel the permit in writing. The consumer's generator should not be reconnected until the interlock is verified.