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TABLE 7-2 Transformer Troubleshooting

Condition

Possible Cause

Suggested Remedy

Hot transformer | High ambient temperature | Improve ventilation or relocate unit to cooler location

Overload

| Reduce load; reduce amperes by improving power factor with capacitors; check for circulating currents for paralleled transformersdifferent ratios or impedances; check for open phase in delta bank |

| High voltage | Change circuit voltage, taps.

Insufficient cooling

| If other than naturally cooled, check fans, pumps, valves, and other units in cooling systems |

| Low oil (or askarel) level | Fill to proper level

Dirty oil (or askarel)

| Filter to remove dirt, sludge, or carbon; clean core, coils, and terminal board with clean, filtered oil or askarel |

| Winding failureincipient fault |

See No voltageunsteady voltage below

Short-circuited core

| Test for exciting current and no-load loss; if high, inspect core, remove and repair; check core bolts, clamps and tighten; check insulation between laminations; if welded together, return to factory for repair or replacement |

Noisy transformer | Overload | See Hot Transformer above

| Metal part ungrounded, loose connection |

| Determine part and reason; check clamps, core other parts normally grounded for loose or broken connections, bolt fallen out, nuts vibrated off, bolts, etc; tighten loose clamps, bolts, nuts; replace missing ones |

| External parts and accessories in resonant vibration |

| Tighten items as above; in some cases, loosen to relieve pressure causing resonance and install shims |

| Extremely low oil or askarel level exposing live parts |

| Check cause (leak, etc.), repair or replace damaged part, refill to proper level |

| Incipient faultcore or winding |

See above under Hot Transformer

Bushing flashover | Lightning | Check lightning protection; arresters, connections, lugs, grounds
| Dirty bushings | Clean porcelains; check source of dirt

Broken bushing or parts

| Strains on terminal connections |

| Flexible connections inserted between terminals and cables or busses to remove strain from bushing |

| No voltageunsteady voltage |

| Winding failurelightning; overload; short-circuit from |

| Check winding, remove foreign object or damaged material; repair or replace parts of insulation materials, if possible, otherwise return to |

| (table continued on next page) |

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