1. Adjust the oil level
The function of the transformer oil level gauge (or oil gauge) is to indicate the oil level in the transformer oil pillow, which can monitor the oil level. If the oil level is too low, it will cause the action of the gas relay, and also affect the heat dissipation and insulation of the transformer, increasing the contact surface between oil and air. Due to the high temperature of the oil in the upper layer, it is easy to absorb the newly entered air, so that the oil is rapidly oxidized and damp. If the oil level is too high, it will cause an oil spill and the respirator will fail. With the oil level gauge, the oil level of the transformer can be monitored to avoid the above adverse consequences.
According to the national standard GB/T 1094, there are three oil level marks on the oil level gauge: -30°C, +20°C and +40°C.
In this way, the oil level is indicated when the oil temperature is at -30°C, +20°C and +40°C, and these marks indicate the oil temperature. The +40°C oil level line and -30°C oil level line of the transformer oil conservator are equivalent to the oil level marks of +40°C and -30°C when the oil temperature is in the stop state. According to these two signs, it can be judged whether the transformer needs to be refueled and drained. When the oil temperature is +40°C, the oil level is still higher than an oil level line of +40°C, indicating that there is too much oil in the transformer. If the load is on, it may overflow, and some should be released at this time; when the ambient temperature is lower than -30°C and the oil level is lower than the oil level line of -30°C, the oil should be replenished.
2. Supplementary oil filling
The frequently performed on-site oil replenishment operations include the lack of oil in the oil conservator (oil pillow) and the lack of oil in the oil-filled casing.
(1) Treatment of lack of oil in the oil conservator (oil pillow)
The lack of oil in the oil conservator (oil pillow) is due to the leakage of oil from the body or the cooler, which causes the oil level of the oil pillow to be too low or no oil level, which is the lack of oil in the transformer body. Usually requires the transformer to be carried out after a power outage. The method is: open the oil filling hole of the oil conservator (oil pillow), and use the oil filter to supply the oil with the same oil number and qualified electrical and physical and chemical properties to the appropriate oil level. It is best not to add oil to the body from the lower section of the transformer tank, mainly to prevent impurities and water at the bottom of the tank, which will cause the insulation to drop. The following introduces several common forms of oil conservator (oil pillow) replenishment methods.
1) Oil replenishment of capsule oil conservator (oil pillow). The main steps are as follows:
① Exhaust the capsule, open the upper vent hole of the oil pillow, and fill the oil pillow with oil from the oil filling pipe until the oil comes out of the exhaust hole, then close the oil filling pipe and the exhaust hole.
② Drain the oil from the accelerator at the lower part of the transformer. At this time, the air naturally enters the inside of the oil pillow capsule through the moisture absorber until the oil level gauge indicates the normal oil level.
2) Oil replenishment of diaphragm oil conservator (oil pillow). The main steps are as follows
① Before replenishing oil, firstly adjust the magnetic oil level gauge to zero position, then open the vent plug on the diaphragm to remove the gas in the diaphragm, and then close the vent plug.
②Inject oil into the diaphragm from the oil injection pipe at the lower part of the gas collecting box to reach a slightly higher oil level than the specified oil level, open the vent plug again, and fully exhaust the gas in the diaphragm until the oil overflows, and the specified oil level is reached after repeated adjustment.
③ When it is found that there is air in the gas collecting box at the lower part of the oil conservator, the exhaust valve should be used to exhaust the air.
④ Oil replenishment when the normal oil level is low. Use the oil filling pipe at the lower part of the gas collecting box to connect to the oil filter, and fill the oil conservator (oil pillow) with oil. When it is found that there is air in the gas collecting box during the oil filling process, the oil filling should be stopped, the valve of the exhaust pipe should be opened, and the air should be exhausted to the outside.
3) Oil filling of the oil conservator (oil pillow) when the oil level gauge has a small capsule. The main steps are as follows.
①After the transformer is overhauled, before the oil pillow is filled with oil, first add oil to the oil level gauge. At this time, it is necessary to open the plug of the oil meter breathing plug and the small capsule chamber, use a funnel to slowly add oil from the oil meter breathing plug seat, and press the small capsule by hand to exhaust all the air in the bag.
②Open the oil drain bolt of the oil gauge, drain the excess oil in the oil gauge and see the oil level in the oil gauge, and then screw on the plug of the small capsule chamber. Note that the breathing plug of the oil gauge does not have to be tightened too much to ensure that the air in the oil gauge can breathe freely.
(2) Treatment of lack of oil in oil-filled casing
For oil-filled high-voltage bushings, when the oil level is lower than the bottom of the oil mark, in the event of a power outage of the transformer, as shown in Figure 1, use a special tool for oil replenishment, and use the qualified oil with the same oil number and withstand voltage higher than 20kV from the bushing. Fill the oil hole of the pipe with oil. If the oil leakage of the casing is serious and it is impossible to judge the oil level drop, the casing should be replaced with a new one.
1-oil-filled casing; 2-oil pipe; 3-oil storage tank; 4-pump