Analysis on causes of switch cabinet discharge:

1. The construction process fails to meet the requirements

The construction process of cable trench in substation is rough, the interior of cable trench is not subject to strict calendering treatment, and the subsequent reconstruction works are carried out brutally, resulting in the collapse of cable trench wall and the failure of cover plate to be placed normally. The sealing of cable trench is not strict with water vapor, and the dust enters the switch cabinet through the gap at the bottom of the cabinet, causing serious condensation and dust accumulation of support insulators, bushings and other insulating parts, resulting in dirt and discharge.

2. Poor heat dissipation effect of natural ventilation

KYN61 switch cabinet mostly adopts closed structure. The internal handcart room, bus bar room, cable room and low-voltage room are also independent of each other. The cabinet structure did not fully consider reasonable and effective natural ventilation and heat dissipation during design and manufacturing. As KYN61 series switchgear is a fully enclosed structure, without air holes, and the outgoing lines are all cable outgoing lines, the moisture on the cable trench is easy to accumulate in the cabinet. In addition, the ventilation in the cabinet is not smooth, when the ambient temperature changes, condensation is easy to occur, resulting in reduced insulation strength. Because a large number of die-casting epoxy resin insulation parts are used in the switchgear, especially the external insulation layer of high-voltage cables, epoxy cast current transformers, phenolic epoxy insulation covers, phase separators and other composite insulation materials have poor hydrophobicity. If the insulation materials are not good, the air humidity is high and the pollution is serious, the operation will lead to moisture absorption and condensation, leading to increased surface leakage current. When the medium is damp, dirty or damaged, due to moisture, the free electrons on the surface of the medium increase, causing the conduction current to increase, and the insulation resistance to decrease accordingly. When the insulation drops to a certain extent, it will cause partial surface discharge flashover, and eventually develop into interphase short circuit or ground short circuit accidents.

How to deal with the discharge of switch cabinet?

1. Optimize the operating environment in the switch cabinet

The most important point of the switch cabinet discharge is to strengthen the damp proof and dust-proof treatment of the substation, clean the 35kV switch room regularly, avoid floating dust in the room, install industrial dehumidifiers in the switch room, and keep the switch room clean and good temperature and humidity environment. The inlet and outlet wire holes and holes in the cabinet shall be sealed with fireproof mud, and SPR-CN-S1 intelligent dehumidifier shall be installed in the switch cabinet. The "SPR-CN-S1" intelligent dehumidifier can avoid the safe distance of insulation inside the switch cabinet due to its small volume and light weight. Microprocessor control technology is adopted, which can be manually and automatically switched into operation. The device consists of an air supply system, a dehumidification system and an intelligent control system. After being inhaled by a fan, the moist air flows through a special air duct. First, it is cooled and dehumidified by the dehumidification system to replace the moist air with moisture. Then, it is uniformly discharged to the outside through a series of drain pipes in the cable room. Then, the dehumidified air is heated to raise its temperature to reduce its relative humidity. After full circulation, the air humidity in the cabinet is reduced to below the condensation point, and the whole dehumidification process is completed.

2. Product inspection and quality control

(1) The inspection of raw materials for the components in the switch cabinet is often referred to as incoming quality control. The main components include vacuum bubble, circuit breaker, epoxy resin insulation, current transformer, voltage transformer, lightning arrester, copper bar, sheet metal, etc. These components shall be tested at the supplier's factory according to the standard and a test report shall be issued. At the same time, partial discharge detection and excitation characteristic test shall be carried out for CT and PT one by one in the field; Sampling inspection shall be carried out for the insulating parts in the switch cabinet. The test items include but are not limited to power frequency withstand voltage test, partial discharge test, temperature rise test, mechanical property test, thermal performance of insulation layer, flame retardant test, X-ray fluoroscopy inspection, etc.

(2) The test and inspection of the overall performance of the switchgear is often referred to as the final quality control. The factory test room of the complete set of switchgear tests the whole set of products to check whether the components match each other and whether the overall performance meets the requirements. Delivery test includes: insulation test of main circuit, insulation test of auxiliary and control circuit, resistance measurement of main circuit, design inspection and appearance inspection, mechanical operation and interlocking test, partial discharge measurement, etc.