Discussion on Transformer Gas Protection

Abstract: This paper elaborates the basic working principle, protective scope, installation method, routine inspection items, operation status and reasons of signal operation of gas protection device and the basic principle and treatment method of accident analysis for gas protection device of oil-immersed power transformers , And proposed anti-accident measures. Keywords: Oil-immersed power transformers, gas protection, treatment methods, countermeasures 1. Foreword At present, most of the power transformers used by our company are still oil-immersed transformers. Since I often work in the transformer design, installation and commissioning and maintenance work, accumulated a lot of knowledge about the transformer, gas transformer protection is now a detailed introduction. 2.Working principle Gas protection is the main protection component of transformer internal fault. It can act sensitively to faults such as transformer turn-to-turn and interlayer short circuit, core failure, casing internal fault, winding internal disconnection, insulation deterioration and oil level descent . When the inside of an oil-immersed transformer fails, the intensity of the oil varies depending on the severity of the fault, as the arc will break down the insulating material and generate a large amount of gas. Gas protection is the use of reactive gas gas relay (also known as gas relay) to protect the transformer internal fault. In gas protection relays, the upper part is a sealed buoy and the lower part is a metal baffle, both of which have sealed mercury contacts. Buoys and baffles can rotate about their respective axes. In normal operation, the relay is filled with oil, the float is immersed in the oil, in a floating position, the mercury contacts open; the baffle is drooping due to its own weight, and its mercury contacts are also broken. When a slight fault occurs inside the transformer, the gas will be generated slowly. When gas rises to the conservator, it will first accumulate in the upper space of the gas relay, causing the oil level to drop. The float will then drop to close the mercury contact. Signal, which is the so-called "light gas"; when the transformer inside a serious fault, it produces a strong gas, the pressure tank instantaneous sudden surge, resulting in a large oil flow to the impact of the direction of the oil pillow, due to oil shock baffles , The baffle overcomes the resistance of the spring and drives the magnet to move toward the reed contact so as to close the mercury contact and connect the trip circuit to trip the circuit breaker. This is called "heavy gas". Heavy gas action, immediately cut off all the power connected with the transformer, so as to avoid accidents to expand, play a role in protecting the transformer. Gas relays have buoyancy, baffle plate, open cup and other different models. At present, most use QJ-80 type relay, the signal circuit connected to the open cup, trip circuit pick up the baffle. The so-called gas protection signal action, which refers to a variety of reasons caused by the opening of the relay cup signal contact closure, light plate light. 3. Protection range Gas protection is the main protection of the transformer, it can reflect all the failures within the tank. Including: multi-phase short-circuit in the fuel tank, winding turn to turn short circuit, winding and core or with the shell between the short circuit, core failure, oil level drop or oil leakage, tap changer poor contact or poor welding wire. Gas protection action quickly, sensitive and reliable and simple structure. However, it does not reflect the fault on the external circuit of the fuel tank (eg on the outgoing line) and therefore can not be used as the only protective device to protect the transformer from internal faults. In addition, gas protection is also vulnerable to some external factors (such as earthquakes) interfere with the malfunction, which must take appropriate measures. 4. Installation method Gas relay installed in the transformer to the storage tank connection pipe, the installation should pay attention to: 4.1 First of all gas valve on the relay valve off strict. If the valve is not strict or there are other circumstances, if necessary, let go of the oil in the pillow to prevent a lot of oil spilled at work. 4.2 Before installing the new gas relay, check whether there is no inspection certificate, diameter, flow rate is correct, both internal and external parts are damaged, internal temporary banding to open apart, and finally check the buoy, baffle, signal and trip contact action is Reliable, and close the bleed valve. 4.3 gas relay should be installed horizontally, the direction of the arrow marked on the top of the cover pointing to the oil pillow, the project allows the direction of the pipe axis of the relay toward the direction of the oil pillow slightly higher end, but with the horizontal tilt should not exceed 4% 4.4 Open the valve Fill gas relay, deflate with bleed valve after filling with oil. If the oil pillow with capsules, should pay attention to the method of oil-filled deflate, try to reduce and avoid the gas into the oil pillow. 4.5 protective wiring, should be connected to the wrong and short circuit, to avoid live operation, while preventing the conductive rod rotation and small porcelain leakage. 4.6 Put into operation, should be carried out insulation test and drive test. 5. Test items Gas relay should be used in the installation of some of the following test items and test items: 5.1 General inspection items: glass windows, deflation valve, control pin and lead terminals and other complete impermeable, buoy, open cup , Windows and other intact crack. 5.2 Test Project 5.2.1 Seal Test: The overall pressure (pressure 20mPa, duration 1h) leak test, there should be no leakage. 5.2.2 terminal insulation strength test: outlet terminal and the outlet terminal withstand frequency voltage 2000v, for 1min, can also be used 2500v megger measuring insulation resistance, rocker 1min instead of frequency withstand voltage, insulation resistance should be 300mΩ or more . 5.2.3 light gas movement volume test: When the accumulation of 250 ∽ 300cm3 air shell, light gas should be reliable action. 5.2.4 heavy gas flow velocity test. 6. routine inspection project power transformer operating procedures DL / T572-95 (hereinafter referred to as the "rules") in the routine inspection of the transformer should first check the gas relay gas, the gas inspection should pay attention to the following points: 6.1 The valve on the gas relay connection should be in the open position. 6.2 Transformer respirator should be in normal working condition. 6.3 gas protection connector should be put into the correct. 6.4 oil pillow oil level should be in place, the relay filled with oil. 6.5 gas relay waterproof cover must be solid. 6.6 relay terminals should not seepage, and should be able to prevent the intrusion of rain, snow, dust, power and secondary circuit to have waterproof, oil and antifreeze measures, and in the spring and autumn to waterproof, oil and Antifreeze inspection. 7. Running transformer in normal operation, gas relay work without any exception. Regarding the operating status of gas relays, the rules include the following provisions: 7.1 Gas protection should be connected to the signal and trip during transformer operation, and the gas protection of the on-load tap-changer should be tripped. 7.2 Transformers in the operation of the following work should be switched to heavy gas protection switch signal: 7.2.1 When using a circuit breaker to control two transformers, when one of them into standby, you should replace the backup transformer re-gas . 7.2.2 filter oil, make up oil, change the submersible pump or replace the adsorbents of the oil purifier, and open and close the valve on the gas relay connecting pipe. 7.2.3 in gas protection and secondary circuit work. 7.2.4 With the exception of oil recovery and deflation of the bleed valve at the top of the gas relay, open bleed, drain and fill valves at all other locations. 7.2.5 When the oil level of the oil surface abnormal increase or suction system is abnormal, need to open the deflation or drain valve. 7.3 During the earthquake prediction, it should be based on the specific circumstances of the transformer and gas relay seismic performance to determine the operation of heavy gas protection. Earthquake caused heavy gas protection operation shutdown transformer, transformers and gas protection should be put into operation before the inspection test to confirm no abnormalities before they can invest. 8. The main reason why gas protects the signal 8.1 Reasons for light gas operation: 8.1.1 The air enters the transformer due to the lack of tightness of the oil filter, fueling or cooling system. 8.1.2 The oil level is lower than the gas relay due to temperature drop or oil leakage 8.1.3 Transformer failure produces a small amount of gas 8.1.4 Transformer short-circuit fault occurs. In the fault current through the role of the oil gap between the oil flow speed, when the oil gap and the outside of the winding pressure difference between the large change, the gas relay may malfunction. Through the fault current makes the winding action fever, when the fault current multiple is large, the winding temperature rises quickly, so that the oil volume expansion, resulting in gas relay malfunction. 8.1.5 gas relay or secondary circuit failure. The above factors may cause gas protection signal action. 9 gas protection device action After the transformer gas protection device action, it should be carefully checked, a careful analysis, the correct judgment, and immediately take measures to deal with. 9.1 Gas protection signal action, immediately check the transformer to identify the cause of action, because no accumulation of air, oil level reduction, secondary circuit failure or caused by the internal confederation of the transformer. If the gas relay has gas off, the gas volume should be recorded, the color of the gas to be observed and the test on the combustible gas. Gas samples and oil samples should be chromatographed to determine the fault nature of the transformer according to the relevant rules and guidelines. Chromatography refers to the gas chromatograph collected on its contained hydrogen, oxygen, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene and other gases qualitative and quantitative analysis, based on the name of the contained components and content Accurately determine the nature of the Confederation, the development trend, and the severity. If the gas inside the gas relay colorless, odorless and non-flammable, the chromatographic analysis of air, the transformer can continue to run, and timely elimination of intake defects. If the gas inside the gas relay is flammable and the dissolved gas chromatographic analysis results abnormalities, should determine whether the transformer outage comprehensive operation. 9.2 Gas relay tripping operation, the cause of the failure to identify the transformer shall not be put into operation. In order to find out the reasons, the following factors should be considered emphatically to make a comprehensive judgment. b. whether the secondary circuit such as protection and direct current is normal; c. whether the appearance of the transformer has any abnormal phenomenon that clearly reflects the nature of the fault; d. whether the gas accumulated in the gas relay is flammable; e Gas relay gas and oil dissolved gas chromatographic analysis results; f. The necessary electrical test results; g. Transformers and other relay protection device action. 10 gas protection anti-accident measures gas protection action, the light of the protection action signal issued to remind maintenance staff immediately on the transformer to deal with; heavy jump off the transformer switch, causing the transformer immediately stop running, can not guarantee the reliability of power supply, Put forward the anti-accident measures of gas protection: 10.1 change the gas float of the relay of the gas relay to the baffle type, the contact is changed into the vertical type, in order to raise the dependability of heavy gas movement. 10.2 To prevent gas relays from short-circuit due to water leakage, rain-proof measures should be taken on the terminals and the cable terminal box. 10.3 gas relay outlet should be used oil line. The lead wires and cables of the gas relay should be connected to the terminals in the cable lead terminal box respectively. 11. Conclusion Transformer gas signal movement, the operator must check the transformer to identify the cause of action and immediately report to the higher-level scheduling and supervisory leadership, the superior leadership should immediately sent to the scene to extract the relay gas samples, oil samples and Body oil samples, respectively, for chromatographic analysis. According to the relevant guidelines and on-site analysis to take appropriate measures to prevent accidents from happening in order to ensure the safe and economical operation of the transformer. References 1. Yinkuning Power Engineer Water Power Press 2. Huo Xiaowei latest power engineering standards and practical book China Radio and Television Press