Air Replenishing Method of SF6 Sulfur Hexafluoride Electrical Equipment

SF6 is an insulating and arc extinguishing medium gas with good properties, which is widely used in switch gear of transmission and distribution system. In order to ensure the long-term safe and reliable operation of SF6 gas electrical equipment, it is necessary to regularly maintain the electrical equipment of SF6 relay, and regularly test the pressure, purity, moisture and other parameters of SF6 gas in the electrical equipment.

Ⅰ. Direct air replenishment of SF6 relay

After the low pressure alarm of the electrical equipment, check whether the indicators such as SF6 gas purity in the switching equipment meet the requirements of the equipment operating instructions, and then determine whether the gas needs to be recovered and replaced according to the requirements of the corresponding operating instructions. When the gas indicators in the equipment meet the requirements, the switch gas chamber can be supplemented with pure SF6 gas to the rated pressure according to the instructions. When the gas index in the equipment does not meet the requirements of safe operation, the gas in the equipment should be replaced by referring to the air replenishment method during maintenance.

Ⅱ. Air replenishment in the process of maintenance of SF6 relay switching equipment

1. Gas recovery

SF6 gas will decompose under the action of arc, producing part of the harmful low fluoride. These decomposed products have strong reaction capacity, and are extremely toxic. When there is water and oxygen, they will react with electrode materials and water to produce a variety of compounds with the complex composition. Therefore, the SF6 gas in the operated switch gear must be recovered and not discharged to the outside. Before power outage for maintenance, all functions of the recovery device should be checked first, and there is no air leakage in the connecting hoses and joints. During recovery, the pressure of the gas chamber in the switch should be less than 1000Pa after recovery. Technical quality control measures for SF6 relays in the gas recovery process.

(1) Before using the rubber hose for gas recovery, clean the connecting part and the inside of the rubber hose to ensure that there is no foreign body residue and no risk of foreign body mixing.

(2) After the rubber hose is used, it is necessary to install anti-foreign body cap to ensure that there is no risk of foreign body mixing.

(3) The recovery device is used for SF6 gas recovery to ensure that SF6 gas is not discharged or there is no spillover, and ensure the SF6 bottom number in the site installation environment.

(4) When the air displacement is carried out after the vacuum of the air chamber to meet the disintegration conditions, the filter is used to ensure that no foreign matter will enter the air chamber through the air displacement.

(5) Air replacement filters should be distinguished from inflatable filters by the use of markings and should not be mixed.

(6) The filter element adopts the spot inspection system. The use state of the filter element is checked and confirmed before use. If it does not meet the use requirements, a new filter element is replaced to ensure that there is no hidden danger of foreign body mixing.

2. Vacuum pumping

The vacuum pumping function is mainly to remove the residual gas in the valve and vacuum dry the water in the valve. The limit vacuum degree of the vacuum device is generally no less than 133Pa. When the vacuum degree is reached, the vacuum pump is generally kept running for a period of time according to the size of the gas chamber, so that the moisture absorbed in the gas chamber can be fully evaporated. The vacuum operation procedure of SF6 relay is generally shown as follows:

(1) First check before use: Check whether the bolt of the device is loose, whether the oil level of the pump group is appropriate, and whether each valve is in the closed position.

(2) Equipment vacuuming: Press the start button of the vacuum pump and slowly open the inlet ball valve of the vacuum pump after the pump set is in normal operation. If multiple devices need to be vacuumed at the same time, open the corresponding interface valves in turn. The vacuum value can be read directly from the electronic vacuum gauge. After vacuum pumping is complete, close all valves and finally press the stop button of the vacuum pump.

(3) If it is necessary to observe the vacuum degree of the equipment statically, close the inlet valve of the vacuum pump and observe the value of the resistance vacuum gauge, which is the true static value.

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