Discussion on gas protection of the hottest transf

2022-09-26
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Discussion on transformer gas protection

1 preface

at present, most of the power transformers used by our company are still oil immersed transformers. Since I worked, I have often participated in the design, installation, commissioning and maintenance of transformers, and accumulated a lot of knowledge about transformers. Now I will make a detailed introduction to the gas protection of transformers

2 working principle

gas protection is the main protection element for internal faults of transformer. It can act sensitively for faults such as inter turn and inter layer short circuit of transformer, iron core fault, internal fault of bushing, internal disconnection of winding, insulation deterioration and oil level drop. When an internal fault occurs in an oil immersed transformer, the arc will decompose the insulating material and produce a large amount of gas, and its intensity varies with the severity of the fault. Gas protection uses gas relay (also known as gas relay) to protect internal faults of transformer

in the gas protection relay, the upper part is a sealed pontoon, and the lower part is a metal baffle, both of which are equipped with sealed mercury contacts. The pontoon and baffle can rotate around their respective axes. During normal operation, the relay is filled with oil, the pontoon is immersed in oil, and is in the floating position, and the mercury contact is disconnected; The baffle sags due to its own weight, and its mercury contact is also disconnected. When a slight fault occurs inside the transformer, the gas is generated slowly. On the way to the oil conservator, the gas is first accumulated in the upper space of the gas relay, causing the oil level to fall, and the pontoon to fall, so that the mercury contact is closed and the delay signal is connected, which is the so-called "light gas"; When a serious fault occurs inside the transformer, strong gas will be generated, and the pressure in the oil tank will suddenly increase, causing a great impact in the direction of oil flow to the conservator. Because the oil flow impacts the baffle, the baffle overcomes the resistance of the spring, drives the magnet to move towards the dry spring contact, closes the mercury contact, connects the tripping circuit, and trips the circuit breaker, which is the so-called "heavy gas". The heavy gas action immediately cuts off all power supplies connected to the transformer, so as to avoid the expansion of the accident and protect the transformer

gas relay has different models, such as float type, baffle type, open cup type, etc. At present, qj-80 relay is mostly used, with its signal circuit connected to the open cup and the tripping circuit connected to the lower baffle. The so-called gas protection signal action means that the signal circuit contact of the upper open cup in the relay is closed and the light plate light is on due to various reasons

3 protection range

gas protection is the main protection of transformer, which can reflect all faults in the oil tank. Including: polyphase short circuit in oil tank, winding turn to turn short circuit, short circuit between winding and iron core or shell, iron core fault, oil level drop or oil leakage, poor contact of tap changer or poor welding of conductor, etc. The gas protection action is rapid, sensitive and reliable, and the structure is simple. However, it cannot reflect the fault of the external circuit of the oil tank (such as the outgoing line), so it cannot be used as the only protection device to protect the internal fault of the transformer. In addition, gas protection is also prone to malfunction under the interference of some external factors (such as earthquake), so corresponding measures must be taken

4 installation method

the gas relay is installed on the connecting pipeline from the transformer to the oil conservator. During installation, attention should be paid to:

6.6, 0.9, 7.8, 2.7 percentage points lower than that in 2013 respectively. 4.1 first, close the butterfly valve on the gas relay pipeline. If the butterfly valve cannot be closed tightly or there are other conditions, drain the oil in the conservator if necessary to prevent a large amount of oil from overflowing during operation

4.2 before installing the new gas relay, check whether there is a certificate of conformity that can fully meet the temperature control indicators specified in the national standard gb229-2007 (American Standard ASTM)), whether the caliber and flow rate are correct, whether the internal and external components are damaged, if there is a temporary binding inside, disassemble it, and finally check whether the action of the pontoon, baffle, signal and trip contact is reliable, and close the vent valve

4.3 the gas relay should be installed horizontally. The arrow direction marked on the top cover refers to its performance, which directly affects the service life of the high-speed railway line. In the project, it is allowed that the direction of the relay's pipeline axis is slightly higher towards the end of the conservator, but the inclination with the horizontal plane should not exceed 4%

4.4 open the butterfly valve to fill the gas relay with oil, and then bleed from the vent valve. If the conservator has this, you can rest assured that the capsule should pay attention to the method of oil filling and deflation, and try to reduce and avoid gas entering the conservator

4.5 when carrying out protective wiring, it is necessary to prevent wrong connection and short circuit, avoid live operation, and prevent the rotation of conductive rod and oil leakage of small porcelain head

4.6 before putting into operation, insulation shake test and transmission test should be carried out

5 test items

before installation and use, the gas relay should be subject to the following inspection items and test items:

5.1 general inspection items:

the glass window, air release valve, control needle and outgoing line terminal are complete and free of oil leakage, and the pontoon, open cup, glass window are complete and free of cracks

5.2 test items

5.2.1 sealing test: the overall refueling pressure (pressure is 20MPa, duration is 1H) shall be tested for leakage, and there shall be no seepage leakage

5.2.2 terminal insulation strength test: the power frequency voltage withstand between the outgoing terminal and the outgoing terminal is 2000V, lasting for 1min, and the insulation resistance can also be measured by using a 2500V megger. The insulation resistance should be more than 300m Ω by shaking for 1min instead of power frequency withstand voltage

5.2.3 light gas action volume test: when 250 ∽ 300CM3 air is accumulated in the shell, the light gas should act reliably

5.2.4 heavy gas action flow rate test

6 daily inspection items

power transformer operation specification dl/t (hereinafter referred to as "the specification") stipulates that in the daily inspection items of the transformer, the presence of gas in the gas relay should be checked first, and the following points should be paid attention to in the inspection of gas:

6.1 the valve on the connecting pipe of the gas relay should be in the open position

6.2 the respirator of the transformer shall be in normal working condition

6.3 the gas protection connecting piece shall be put into operation correctly

6.4 the oil level of the conservator should be at the appropriate position, and the relay should be filled with oil

6.5 the waterproof cover of gas relay must be firm

6.6 there should be no oil leakage at the relay terminal, and it should be able to prevent

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