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Page 123

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Condition

Possible Cause

Suggested Remedy

| foreign object or low strength dielectric (oil or askarel) |

| factory, replace oil or askarel; check relief diaphragms and seals for entry of moisture |

Leaks

| Cracks; holes; loose bolts or poor threading; imperfect welds, improper assembly; poor gasket installation |

| Repair damaged parts, or replace, if possible, otherwise return to factory; check and tighten bolts, clamps on cover, hand-holes, bushings, etc. Replace gaskets, do not attempt to salvage them |

Rust and paint deterioration

| Weather, polluted or salt atmosphere; overloads |

| Remove rust and deteriorated paint; clean surfaces; repaint with proper paints and sufficient coatings |

| Low dielectric strength of oil or askarel |

| Dirt; moisture; sludge or carbon |

| See Hot Transformers; No voltageunsteady voltage; Leaks above |

LINE TROUBLES AFFECTING TRANSFORMERS

Overload
Hot neutral line

| Too small neutral conductor; replace; severe unbalance between phases; rebalance and equalize loads |

One leg of wye bank open

| Check associated fuse; if blown, remove cause and replace; check for open circuit in winding of transformer in bank |

Voltages unbalanced

| Open neutral unbalanced loads |

Check neutral connections; see Hot neutral line above

| Voltages high and unbalanced |

| Open neutral on wye bank ground in winding of one transformer in wye |

| Check neutral connections and load balance; check values of voltages between phases and phase to ground voltages; vector should indicate source of trouble |

| Flashover of bushing on delta-connected bankfuse possibly blown |

Ground on one leg of delta

Transformer winding not designed for full phase-to-phase voltage

| No voltageone phase of delta connected bank |

| Grounds on two legs of delta (delta collapseloads single phasing) |

Remove grounds from at least one leg of delta source

| Overloads on two transformers in delta bank |

| Open in third transformer of bank; operating in open delta |

| Check fuses on supply to their bank; check winding of third transformer for continuity |

| Low voltage on two phases of delta |

| Open in one phase of delta supply; two transformers now connected across one same phase |

Check fuse on supply; check supply circuit back to source for open circuit

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