Internal arc fault pressure release device

The internal arc fault test of medium voltage switchgear used to require the installation of a simulated ceiling 600mm away from the top of the switchgear for testing. However, the new standard has removed this requirement. If the simulated ceiling is not installed on the test site, that is, if the laboratory top is more than 2 meters away from the switchgear pressure relief cover plate, the pressure relief cover plate can be opened directly, and the arc can be directly sprayed upwards. Even if it bounces back to the top, it generally will not ignite the level indicator.

If a simulated ceiling is required to be installed 600mm away from the top of the cabinet, spraying directly upwards from the top of the switchgear will cause the indicator to rebound and ignite, which is a highly probable occurrence.

However, domestic customers generally do not have the space for the internal arc of the switchgear to be released outside the building. The internal arc of the switchgear can only be released inside the building, and direct release will rebound and ignite the indicator. Domestic customers generally cannot accept the design of installing baffles on the top of the cabinet, front, back, left, and right. Therefore, a solution must be designed to meet the above problems.

The specific requirements are as follows:

1. Prevent the arc from rebounding and igniting the level indicator to ensure the test passes.

2. As an integral part of the switchgear, it is necessary to provide integrated supply in actual projects, rather than adding additional equipment.

In addition, the solution should not affect the temperature rise of the switchgear, especially the heat dissipation of high current switchgear; The plan cannot delay the release of pressure and additionally increase the destructive pressure that the cabinet can withstand.

It should be clarified that the solution to the device is to ensure that the sprayed flame will not ignite the level indicator, smoothly pass the arc test, and ensure the safety of the operators in front and on the side of the cabinet. It is not a restriction on flame spraying. Flame spraying is prohibited in industrial specific places, such as some chemical and coal mines, where open flames are prohibited. Even if internal arc faults occur, flame spraying is not allowed. This requires special design, and switch cabinets also require higher strength cabinets.

Installing a buffer compartment on the top of the switchgear is a simple and feasible method. The height of the buffer compartment needs to ensure that the pressure release plate on the top of the cabinet can be opened normally, that is, when an internal arc fault occurs, the pressure release plate is opened by the internal arc shock wave as soon as possible, thereby quickly releasing pressure and reducing further impact on the cabinet structure.

After the pressure is released into the buffer compartment, it is first diluted by the large volume of the buffer compartment, especially when there are many switch cabinets in a row, the wider the width, the more obvious the dilution effect.

Entering the buffer compartment does not solve the problem, and it needs to be released to a larger space outside the switchgear. If the pressure release plate form is continued, on the one hand, a large impact pressure is required. If the release plate is not in the direction directly reached by the shock wave, it is difficult to open, and the pressure will rebound into the cabinet, causing further damage to the switchgear.

On the other hand, during normal use, the buffer compartment is in a completely sealed state, which is not conducive to temperature rise and heat dissipation. The hot air needs to be released through the window. The hot air discharged from the top of all switchgear accumulates heat inside the sealed compartment and cannot be released.

Therefore, adopting a two-sided ventilation method can prevent the arc from directly spraying upwards and rebounding. For example, this method is used for marine switchgear, effectively reducing the ceiling height of the switchgear installation room.

Experimental verification shows that for the internal arc fault test of IAC AFLR 31.5kA 1s, the above scheme can pass the test smoothly without causing combustion to the level indicator. The temperature rise of the switchgear is not affected and is suitable for engineering use.