There are many reasons for abnormal discharge in the high pressure through-wall casing, one of which is caused by the existence of air gap. Therefore, in order to reduce or eliminate the discharge in the high pressure through-wall casing, the following solutions can be adopted:
1. Reduce the air gap
The potential line near the electrode only passes through a single medium (solid porcelain medium). Generally speaking, the field intensity near the electrode is always large. If the potential line runs through the gas and solid porcelain medium, it is similar to the situation in the gap, and the field intensity in the gas part is inevitably strengthened, resulting in gas flasticity, breakdown and discharge. Therefore, the busbar can be passed through the bushing part to increase the busbar thickness, eliminate the air gap between the busbar and the porcelain insulation, and improve the flasticity discharge voltage. In this scheme, the load bearing capacity of the long bus bar is increased. As a result, the bus bar is prone to deformation when it runs for a long time.
2. Add barrier to electric field
A solid insulating material (such as paper and cardboard) is placed in the highly uneven air gap in the casing, which is called the barrier. In this way, the dielectric coefficient can be significantly improved under certain conditions, and the corresponding breakdown voltage is also increased. The scheme is filled with cardboard materials in the air gap, which requires the design and production of material molds. The cost of materials is not high and the construction is easy. However, the cardboard materials are susceptible to moisture and long-term use of air humidity, and the dielectric coefficient is large, the breakdown voltage is reduced, and the discharge is easy.
3. Replace the new high pressure wall casing
At present, the inner surface and outer surface of the wall piercing sleeve produced by domestic manufacturers are equipped with shielding nets. The inner surface shielding net is connected with the busbar to form equipotential, and the outer surface shielding net is connected with the ground, which eliminates the breakdown and discharge caused by uneven electric field. The replacement of the new casing requires customization, and the cycle is long. Considering that the operation of the equipment with disease is easy to cause accidents, and the users are all oilfield production units, which indirectly affects the production capacity construction of the oilfield and mining area. In addition, the transformation cost is also high.
4. High pressure closed cabinet transformation
The 35kV high voltage closed cabinet is transformed into an open type high voltage cabinet, the core bushing is cancelled, and the busbar in the cabinet is connected through to reduce the power supply. This scheme makes the electric field in a single air medium, and the technical demonstration is feasible. It needs to expand the opening aperture of the original cabinet, so that the discharge distance can meet the 35kV AC voltage level. The reconstruction construction difficulty is low, almost no other materials are added, and the reconstruction cost is low.
