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Page 60

| a suitable length to take a sample from the bottom of the tank where sludge and water usually settle. |

| Tap changers (if they exist) should be checked for proper position and for the condition of the contacts. Discoloration of the contact may indicate excessive heat. A tap changer set between or on two tap contact points may prevent the transformer from operating or may cause excessive heating in portions of the winding between the two tap contacts. |

| Core, coils, terminal boards, and connections should be inspected for signs of heat discoloration. These may be caused by overloading, from loose connections, or from loose core laminations due to improper bracing. |

| In large transformers, water cooling coils should be carefully inspected and tested. Lagging or insulation of the water pipes above the oil level should be intact or condensation may form, affecting the insulating quality of the oil. The rate of water flow should also be checked; if found to have diminished, the cause should be looked for and remedied. Scale formed inside the cooling pipes may be removed by circulating a solution of hydrochloric acid through the pipes. Scale formed outside the cooling pipes may be removed by wire brushings. |

| Radiators should be inspected for dents and holes which may cause restriction of the flow of coolant or leakage, eventually causing the transformer to overheat. |

| Maintenance.. |

| Ordinary mechanical maintenance should be performed in the normal manner. Rusted and corroded areas should be cleaned before repainting. Connections, similarly, should be cleaned before remaking or retightening. |

| Oil |

| Usually, the first thing checked in determining the condition of a transformer is the oil. In a transformer, oil not only acts as insulation but also provides a medium which carries heat away from the windings. Hence, it should not only have high dielectric strength, but should have low viscosity to provide good heat transfer. It should also be free of sulphur and other corrosive agents which might injure the insulation, conductors, and other metallic parts, it should not permit moisture particles to remain in suspension but allow them to settle quickly to the bottom, and it should be free from sludging under normal operating (heat) conditions. |

| The condition of the oil may be determined in the field by two simple tests. The first simply compares the color of a sample of the oil from the transformer with a panel of several standard colors which give some indication |

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