How to deal with the excessive acetylene gas in transformer insulating oil
2019/12/19??????view:
Main functions of transformer oil:
(1) Insulation function: transformer oil has much higher insulation strength than air. The insulating material soaked in oil can not only improve the insulation strength, but also avoid the erosion of moisture.
(2) Heat dissipation: the specific heat of transformer oil is large, and it is often used as coolant. The heat generated during the operation of the transformer makes the oil close to the iron core and winding expand and rise by heating. Through the convection of the oil up and down, the heat is released through the radiator to ensure the normal operation of the transformer.
(3) Arc suppression: on the on load voltage regulating switch of oil circuit breaker and transformer, arc will be generated when the contact is switched. Because the transformer oil has good thermal conductivity and can contact a large number of gases under the action of high temperature of the arc, it can generate a large amount of pressure, thus improving the arc extinguishing performance of the medium and making the arc extinguish quickly.
The performance of transformer oil usually has the following requirements:
(1) The density of transformer oil shall be as small as possible to facilitate the precipitation of moisture and impurities in the oil.
(2) Viscosity should be moderate, too much influence convection heat dissipation, too small will reduce flash point.
(3) The flash point shall be as high as possible, generally not lower than 136 ℃.
(4) The freezing point shall be as low as possible.
(5) The lower the content of acid, alkali, sulfur, ash and other impurities, the better, so as to avoid their corrosion to insulating materials, wires, oil tanks, etc.
(6) The degree of oxidation should not be too high. The degree of oxidation is usually expressed in terms of acid value, which refers to the amount of potassium hydroxide (mg) needed to absorb the free acid in 1g oil.
(7) The stability shall not be too low. The stability is usually represented by the precipitate of acid value test, which represents the anti-aging ability of oil
Index reference of new transformer oil:
Transparent appearance, free of suspended matter, sediment and mechanical impurities
Flash point (closed cup) ≥ 135 ℃
Kinematic viscosity (50 ℃) < 9.6 × 10-6m2 / S
Acid value ≤ 0.03mgkoh/g
Pour point < - 22 ℃
Treatment method for acetylene gas exceeding the standard:
1. Using gas chromatography to analyze dissolved gas in oil to detect internal fault of transformer is an important means to ensure its normal and safe operation. During the operation of transformer, due to overheat and discharge fault, acetylene gas is usually produced, which will seriously damage the equipment.
2. Through the analysis of a typical example of a 220kV transformer, it shows how to diagnose and deal with the fault when acetylene gas appears in the transformer, although it does not exceed the value of attention, but it shows a slow growth trend.
Fault overview: in the routine analysis of transformer oil at the beginning of 2002, the characteristic gas C2H2 was found in the oil, with the content of 0.21ppm, and other indexes were normal. In order to prevent misjudgment, take oil samples for retest, and the test results are basically the same as the last time.
3. It is preliminarily determined that the transformer may have slight electrical fault or discharge fault.
Troubleshooting:
Then, the transformer was monitored and analyzed once in half a month. The tracking analysis data are as follows:
Through the data, it can be found that C2H2 shows a slowly rising trend, and other gases have no obvious change, so it is basically determined that there is a spark discharge fault (low energy discharge) in the transformer.
Since the C2H2 content has not affected the normal operation of the transformer, it is decided to find out the cause from the auxiliary equipment. During the inspection, it is found that the pointer of oil flow relay of oil pump in the cooler sometimes vibrates irregularly and violently. After the circuit is checked to be normal, only slight oil leakage trace is found at the root of the terminal block when the junction box is opened, and all lead screws are fastened well.
After the power supply is restored, the problem still exists, which may be the internal failure of the submersible pump. Then close the inlet and outlet valves of this group of oil pumps, open the fixed sealing plate of the terminal post, and find that the root of the internal lead terminal of the oil submersible pump is broken, and there are traces of discharge burns at the broken joint, so it is determined that C2H2 is generated due to the discharge at this place.
4. Summary:
After the connection terminal is replaced, the oil flow relay of the submersible pump operates normally. At the same time, the oil sample is taken for tracking analysis. The content of C2H2 has declined, which indicates that C2H2 has been absorbed by insulation, etc., effectively avoiding the fault.
During the operation of transformer, it is necessary to take oil samples regularly for chromatographic analysis, and pay close attention to the change of characteristic gas content. No matter whether the oil contains inflammable and explosive acetylene or the total gas content exceeds the standard, it will seriously affect the insulation performance of the oil. Therefore, when the detection is unqualified, it is recommended to use Zhongjing brand vacuum degassing and filtering device (high efficiency two-stage vacuum oil filter) to remove gas or effectively reduce the treatment of transformer oil.
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