Oil-Immersed Transformers have several separate oil systems. During the operation of oil-immersed transformers, the oils in these oil systems are not connected to each other, and the oil quality and operating conditions are different. Chromatographic analysis of the gas in the oil should be performed separately to identify potential problems.
Oil in the high pressure outlet box or oil in the gas outlet box. The high voltage outlet of the three-phase 500kV transformer passes through the corrugated insulation and oil isolation system. The main function of this oil system is insulation. In order to simplify the structure, the oil system can also be connected with the oil system in the main body by connecting pipes, or planned into a separate oil system.
Two, completely sealed, voltage level of 60kV and above. This oil system mainly plays the role of insulation, or the electrical strength oil of insulating paper is added to the capacitor sleeve. When the main body is filled with oil, the terminal of the casing end should be sealed to prevent air intake.
3. Oil in the loaded tap changer chamber. This part of the oil has its own maintenance system, namely flow relay, oil storage tank and pressure relief valve. The oil in the switch chamber has the effect of insulating and quenching the current. When the switch blocks the load current, the oil will be discharged from the resulting oil. The oil system should have a good sealing function, which should be maintained even if the arc pressure occurs during the switching process.
Although the oil in the switch chamber of the on-load tap changer is isolated from the oil in the main body, the vacuum oil injection should be carried out simultaneously with the oil in the main body in order to prevent damage to the seal of the switch chamber during the vacuum oil injection. For vacuum oil injection, both systems should have the same degree of vacuum. If necessary, the oil storage tank of the system should also be blocked during the vacuum process. In order to facilitate the structure, the main oil storage tank and the transfer switch room oil storage tank are planned to be isolated from each other as a whole.
Iv. Oil system in the main body. The oil system connected with the oil around the winding is the main system, including the oil in the refrigerator or radiator, the oil in the oil storage tank and the oil in the oil-filled casing at 35kV and below. During the refueling process, the exhaust plug stored in the oil system shall be discharged. In general, the above components shall have their own exhaust plugs. The oil in the main body mainly plays the role of heat preservation and cooling.
Electrical strength of insulated cardboard. During vacuum refueling, if some components cannot accept the same vacuum strength as the main tank, temporary gate valves should be used for plugging, such as the gate valve between the storage tank and the main tank. The head of the submersible pump on the refrigerator shall be sufficient to prevent air inhalation due to negative pressure. The oil system shall have a maintenance system for pressure relief equipment to eliminate pressure in the event of plant failure.
V. When conducting various insulation tests on oil-immersed transformers, the first is to release the gas that may be stored through the exhaust plug. By analyzing the gas content in the oil of each system, chromatographic analysis can predict whether there is a potential problem. Each oil system should meet the operation requirements, such as the change of oil volume when absorbing oil expansion and contraction, oil discharge valve, exhaust plug, isolation valve between refrigerator and radiator, main oil tank, etc., each oil system has a good sealing function. The oil in the on-load tap changer can be replaced separately without discharging the oil in the main body. During transport, the oil in the main body can be discharged and filled with dry nitrogen gas.
