Pressure release of anti internal arc fault switchgear

Internal arc fault in switchgear is an explosion. Due to the concentration of huge arc energy in a small space, the shock wave generated by the explosion radiates in all directions at the speed of light. When it reaches the blocking part, negative pressure is generated, and the pressure suddenly increases, causing astonishing damage. Energy needs to be released in order to reduce damage. Relatively weak links will be broken first, and the pressure will be quickly released and reduced. This is why metal enclosed switchgear needs a pressure relief cover plate. Whether it is an air insulated switchgear or a gas insulated switchgear, a pressure relief device ARS is required.

The bottom or top of the inflatable cabinet is equipped with pressure relief valve plates, which can withstand normal pressure changes without leakage, and can break through and release pressure when the pressure is too high.

The pressure release plate of an air insulated switchgear is usually located at the top of the cabinet, with one end fixed with metal bolts and the other end fixed with nylon bolts. When the internal arc occurs, the pressure breaks the nylon bolt and opens the cover plate. The metal bolt fixing side of the cover plate undergoes permanent deformation, and the cover plate remains in the open position, continuously releasing pressure. However, using hinges for fixation may cause rebound and not always remain in the open position, which is not conducive to pressure release.

It should be noted that experiments have shown that using a W-shaped grid board as the top relief plate for high current switchgear has a large ventilation area and meets IP4X requirements. Most importantly, it can also be quickly opened in case of internal faults. The top fan and other forced ventilation facilities can also be automatically turned on without affecting pressure release.

Possible reasons

No matter how sophisticated the switchgear is, internal arc faults, incorrect installation, insulation damage, misoperation, corrosion, improper assembly, insulation, contact or valve damage and deformation that can change the state of the withdrawable handcart, ferromagnetic resonance of voltage transformers, low voltage side short circuits, poor maintenance, staff errors, aging under long-term high temperature electric fields, pollution, moisture, dust, animal entry, overvoltage and other factors may all lead to internal arc faults.

The design of the switchgear must have a pressure relief channel

Internal arc faults may occur in various high-voltage compartments, therefore each compartment must have a pressure relief cover plate. A typical KYN28 switchgear has a top pressure relief cover plate in each medium voltage compartment, and a pressure relief channel connected to the pressure relief cover plate ensures that the airflow can flow smoothly and effectively to the cover plate in case of internal arc faults, breaking through the cover plate and reducing the pressure inside the switchgear compartment.

For ring main units, due to the short circuit value of only 20kA and low internal arc energy, pressure relief is generally achieved through cable trenches, which is a direct and effective measure. The installation space and pressure relief space inside the cable trench are separated to reduce cable damage. There are also outdoor switch stations or 36kV ring main units installed on wind towers, where it is inconvenient or impossible to release pressure in cable trenches. A rear pressure relief channel is used to release pressure at the top of the cabinet.

Pressure relief of double-layer switchgear. The difficulty of pressure relief in double-layer cabinets lies in the release of pressure in the lower handcart compartment and lower cable compartment, which requires a channel for release and does not allow pressure release through other compartments. Therefore, there is a patented design that uses the upper part of the lower handcart compartment and the rear of the instrument room as a shared pressure relief channel. In this way, the lower handcart room, lower cable room, and busbar room can all release pressure to the upper compartment without circuit breakers through this channel, and release it outdoors through the cabinet top channel.

The pressure relief of the shared pressure relief channel. Each high-voltage compartment has a separate pressure relief plate nearby, which is released to the safe area at the top of the cabinet through a shared channel.

A horizontal pressure relief channel is used to release the pressure generated by internal arcs, such as arc light combustion, to a safe area outside the switch room. The switch room is not affected by electric arcs, and all other facilities are not burned.