Causes and Countermeasures of gas protection actio

2022-10-21
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Causes and Countermeasures of transformer gas protection action

according to the regulations, outdoor transformers above 1000KVA and indoor transformers above 320kva should be equipped with gas protection as the main protection of the transformer. Gas protection has the advantages of fast action, high sensitivity and simple structure, which can reflect various types of faults inside the transformer oil tank. Especially when the number of short-circuit turns of the winding is small, the fault circulating current is large, which may cause serious overheating, but the change of external current is very small, and various protections reflecting current are difficult to act. Gas protection has special advantages for this kind of fault

1 use safety measures

for a long time, the correct action rate of gas protection is lower than the average level of other protective devices of transformer. In order to improve the safety and reliability of gas protection, in addition to improving the structure of gas relay, the following safety technical measures need to be implemented

the transformer should have a slope of 1% ~ 1.5%. The oil pipe leading to the relay should have a slope of 2% - 4%, and the oil conservator is high, which makes the gas easy to flow into the gas relay. The outgoing line of the gas relay should be oil proof wire or plastic wire, which passes through the intermediate junction box and is connected through the terminal strip and cable. The cable and outgoing line should be connected on both sides of the terminal strip in the junction box respectively. The outgoing line is connected from the lower part of the terminal strip, and the cable is led out from the upper part of the terminal strip, This wiring is to avoid corrosion of cables caused by capillary phenomenon of oil. In addition, it should also be noted that the lead arrangement should separate the heavy gas contact from the positive pole of the DC power supply, and the intermediate terminal box should not be placed under the oil pipe and conservator to prevent oil leakage from penetrating the terminal box

to prevent the contact outgoing line of the gas relay from being short circuited due to water leakage, the end cover of the gas relay and the small terminal box of the cable outgoing line shall be sealed to prevent misoperation caused by rainwater immersion

the outlet intermediate relay of the gas relay should be equipped with a self holding coil to prevent the instability of oil speed in case of serious internal fault of the transformer, which will cause the gas contact to be on and off and cannot trip reliably. According to the diameter of the reinforcement product, the breather of the transformer must be kept unobstructed. Before the transformer is put into operation, it is necessary to check whether the vent hole at the lower part of the moisture absorber is opened. During operation, the air permeability of the moisture absorber should also be checked to prevent the malfunction of the gas relay due to the vacuum or pressure rise of the respirator or conservator caused by the blockage of the air vent when the transformer oil temperature changes

the connecting valve between the gas relay and the oil conservator should be opened during operation. In order to prevent gas misoperation caused by forgetting to open after maintenance, the valve should be sealed with lead

when the transformer is running, the heavy gas should be connected to the tripping signal, and the light gas should be input to the signal. The gas of the standby transformer should be put into the signal, so as to monitor the oil, which is suitable for the tensile, peeling, deformation, tearing, heat sealing, bonding, puncture force, opening force, low-speed unwinding force and other performance test surfaces of plastic film, composite materials, adhesives, adhesive tapes, self-adhesive, medical patches, protective films, release paper, backplane materials, rubber, paper fibers and other products. The single standby transformer shall be disconnected from the tripping power supply. When one circuit breaker controls two transformers, if one of them becomes standby, its heavy gas shall be connected to the signal

before the transformer is put into operation after oil filtration, refueling, silica gel replacement or maintenance of radiator and submersible pump, the heavy gas should be connected to the signal first, and the heavy gas can be put into the tripping position only after the air is exhausted

when the oil level indicated on the oil level gauge rises abnormally or the oil circuit system has abnormal phenomena, in order to find out the cause, it is necessary to open each vent or oil drain plug and valve, check the moisture absorber, or when carrying out other work, the heavy gas must be connected to the signal first, and then the work can be carried out to prevent the misoperation and tripping of gas protection

2 watts, thereby improving the service life of the road, is the main reason for the action of the protection signal

if the gas protection action, the transformer switch trips, in general, the accident process has ended, and the consequences are relatively serious. Therefore, when the gas signal acts, it must be carefully checked, carefully analyzed, correctly judged, and immediately taken measures. Transformer gas relay has different models, such as float type, baffle type, open cup type, etc. at present, qj-80 gas relay is mostly used. Its signal circuit is connected to the open cup, and the tripping circuit is connected to the lower baffle. The so-called gas protection signal action refers to the light gas action when the signal circuit contact of the upper open cup in the relay is closed due to various reasons. The reasons for contact closure generally include the following aspects

the air enters the transformer and gradually gathers on the upper part of the gas relay, forcing the oil level in the relay to drop, making the dry spring contact close and sending a light gas signal. There are three ways for the air biotechnology gas to enter the transformer in operation: first, when the transformer is changing or adding oil, the oil to be changed or added is not completely deaerated by vacuum, and it is strictly carried out according to the vacuum oil injection process, so that the air in the oil, the air attached to the core, winding, accessory surface and the air in the pores of organic solid insulating materials, will expand and contract the magnetic circuit of the transformer core through the convection circulation of oil after the transformer is put into operation, Gradually gather and rise to the gas relay, causing signal action. Second, after the adsorbent (such as silica gel) of the transformer thermosyphon is replaced, the oil immersion and standing time are short, and the air is not completely discharged. The thermosyphon enters the body for circulation, and enters the gas relay to cause signal action. Third, the submersible oil pump of the transformer with strong oil circulation is poorly sealed, and the micro negative pressure generated by the oil pump during operation causes the air to enter the transformer body for circulation and gather in the gas relay, causing the gas signal action

the ambient temperature drops suddenly, and the transformer oil shrinks quickly, causing the oil level to decrease, or the oil level in the transformer is reduced due to serious oil leakage of the transformer body, that is, the so-called oil flow causes the signal action of the gas relay

gas relay secondary signal circuit fault, including signal cable insulation damage and short circuit, terminal block contact short circuit, individual signals connected in the signal circuit, etc. cause the dry spring contact to close, resulting in gas signal action

there is a discharge or overheating fault in the transformer, which causes the decomposition of solid insulating materials, the decomposition of transformer oil, and the generation of hydrogen, carbon monoxide, carbon dioxide, and low molecular hydrocarbon gases. These gases gradually become bubbles with the convection circulation of oil and rise and gather in the upper part of the gas relay, forcing the oil level in the relay to drop, causing the gas signal action

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