It is customary to count the time spent by the active part in air from the start of draining the oil from the transformer until it is filled with oil or until the start of evacuation before filling the oil.
The temperature of the active part is measured by a thermosignal or a thermometer mounted on the upper yoke through the hatch in the lid. Do not use a mercury thermometer. Transformers of I — III dimensions on the manhole cover do not, therefore, the temperature of the active part is judged by the temperature of the upper layers of oil. With Surplec you can be sure of the best address of the whole process now.
In recent years, to protect the transformer insulation from moisture during depressurization and oil drainage, deep-dried air with a relative humidity of 20% or less is supplied to the transformer tank. This method does not require heating of the active part and allows you to extend its residence time outside the oil up to 100 hours. Deeply dried air is obtained in special installations (“dry”) with a zeolite adsorbent and an air heater.
Disassembly And Repair Of Separate Transformer Parts
Before disassembling, the transformer is thoroughly inspected from the outside and external malfunctions are detected, oil leakage, mechanical damage to the tank and expander, chips and cracks in the porcelain bushings, assess the condition of the reinforcement putty and the flanges of the bushings, seals, check the serviceability of the breakdown fuse, oil indicator and thermometer. Identified defects are entered in the statement of the technical condition of the transformer. In order to more fully identify defects (lack of oil leaks) in the welds of the tank and other welded and cast parts of the transformer, it is tested with excess oil pressure. After this, the oil is drained from the transformer and disassembled. If the active part of the tank is not planned to be removed from the tank on the day of dismantling the external transformer devices and breaking the cover (as is often the case when repairing large transformers), the oil is drained to the level of the upper yoke so that the insulation and windings remain in the oil. This reduces the time spent by the active part in the air.
- If the repair of the active part and the tank is scheduled to be completed in one step or the active part needs to be dried, the oil is drained completely through the bottom valve of the tank. For transformers of dimensions I and II, oil is usually drained by gravity, for more powerful ones, it is pumped out.
- If the oil is suitable for further use, it is poured into a clean tank with a hermetically sealed hatch. Defective oil is poured into a separate container.
For opening and lifting the active part, the hook of the lifting mechanism is set so that its axis passes through the center of gravity of the transformer. In this case, when lifting, the active part does not touch the tank walls. After that, the nuts and bolts of the devices located on the cover are unscrewed using bilateral open-end horn, socket and adjustable wrenches. The most common are carob, having on each side of the pharynx corresponding to the size of the head of the bolt or nut.