Defect treatment of the hottest HGIS operating mec

Defect treatment of HGIS operating mechanism

summary 411.9: with the continuous expansion of power scale, a large number of ultra-high voltage substations have increased. Due to the pressure of environment and land occupation, the selection of main equipment of EHV 500kV substation in China is very important. At present, there are two main categories of 500kV EHV switchgear in China: gas insulated metal fully enclosed switchgear GIS and conventional open switchgear AIS. GIS has the characteristics of small land occupation, high operation reliability, strong anti pollution and anti-seismic ability, but it is expensive, difficult to repair in a short time after failure and difficult to expand. AIS is cheaper than GIS, but it covers a large area and has more exposed live parts, which limits its application in places with narrow substation area and poor environmental conditions

key words: HGIS operating mechanism defect treatment with the continuous expansion of power scale, a large number of ultra-high voltage substations have increased. Due to the pressure of environment and land occupation, the selection of main equipment of EHV 500kV substation in China is very important. At present, there are two main categories of 500kV EHV switchgear in China: gas insulated metal fully enclosed switchgear GIS and conventional open switchgear AIS. GIS has the characteristics of small land occupation, high operation reliability, strong anti pollution and anti-seismic ability, but its price is expensive, and it is difficult to repair in a short time after failure. For example, PTFE weaving processing and expansion are difficult. AIS is cheaper than GIS, but it covers a large area and has more exposed live parts, which limits its application in places with narrow substation area and poor environmental conditions. HGIS (hypid gas insulated switchgear) is a new type of high voltage switchgear between GIS and AIS. The structure of HGIS is basically the same as that of GIS, but it does not include bus equipment. Its advantage is that the bus is not installed in the SF6 air chamber and is exposed, so the connection line is clear, concise and compact, the installation and maintenance are convenient, and the operation reliability is high. 500kV HGIS is the first to be used in Guangdong power 500kV Hengli substation in China. The station is equipped with 8 groups (each group of three-phase) of Mitsubishi HGIS, of which 4 groups are double circuit breakers, and each phase leads a bushing at both ends and between the two circuit breaker bays. The other 4 groups are single circuit breakers, and each phase leads a bushing at both ends of the Bay. There are 12 circuit breaker bays in the whole station, forming 4 complete strings. Each complete string is composed of a group of double circuit breakers and a group of single circuit breakers HGIS. Since it was put into operation in November 2003, the HGIS equipment has operated stably, but some defects have occurred in the OM-3 hydraulic operating mechanism matched with the circuit breaker. Now the analysis and treatment are introduced as follows. 1. Defect of zero voltage slow opening of circuit breaker mechanism. When the circuit breaker of the station is in the closing state and the mechanism hydraulic pressure drops to zero voltage, some circuit breakers will automatically open slowly. The closing state of the circuit breaker is maintained by the high-pressure oil of the hydraulic mechanism acting on the working cylinder piston through the crank arm and lifting rod. When the high-pressure oil drops to zero pressure, the weight of the lifting rod and connecting plate of the circuit breaker is large, and the working cylinder piston loses the maintenance force of the high-pressure oil and cannot keep the circuit breaker in the closing position. Add a mechanical anti slow separation device in the OM-3 hydraulic mechanism box. The device is composed of high-strength elastic steel sheets of support and I-shaped support, and the installation position is on both sides of the lifting rod in the hydraulic mechanism box. First, remove the four bolts at the corresponding position between the bottom of the lifting rod seal cylinder and the lifting rod head, replace the four new matching long bolts, and fix the anti slow separation support at the bottom of the lifting rod seal cylinder. Then fix the I-shaped support and high-strength elastic steel sheet on the support, both sides are symmetrical, and the elastic steel sheet is processed into an angle. When the circuit breaker is in the closed state, the angle of the elastic steel sheet is located about 0.3~0.5 mm below the lower corners on both sides of the lifting rod head. When the hydraulic pressure drops to zero pressure and the lifting rod of the circuit breaker moves downward slowly, the high-strength elastic steel sheet will hook the lower corners on both sides of the lifting rod head, thus preventing slow opening. Figure 1 and Figure 2 are the schematic diagrams before and after installation respectively. After the mechanical anti slow separation device is installed, because the anti slow separation device has two corners, during the normal operation of the circuit breaker, the lifting rod head will line up the elastic sheets on both sides and cause friction, but the power consumed is very small compared with the operating power, which basically has no impact on the mechanical characteristics of the circuit breaker. Table 1 shows the comparison of the test data before and after the installation of 5012 and 5013 circuit breakers. 2 hydraulic mechanism oil pump pressurization failure defect when the oil pressure in the hydraulic mechanism in the station is manually relieved to zero pressure, the hydraulic oil pump of some circuit breakers cannot build pressure. In terms of 500 kV utilization of this type, in the work of installing anti slow separation device in HGIS of Hengli substation, it was found that the oil pump of 10 of 36 phases of circuit breaker idled and failed to apply oil pressure. At first, it was suspected that the pressure relief valve rod was jammed and failed to reset. After disassembling the pressure relief valve, polishing and reassembling the valve rod, the fault still remained. Under normal pressure, when continuing to check and remove the high-pressure oil pipe connected to the hydraulic pump box, it is found that there are many gases in the hydraulic pump box and the high-pressure oil pipe, and their technical requirements are shown in Table 1. After repeatedly starting the oil pump and repeatedly discharging the gas, the oil pump can build pressure. The hydraulic system of the circuit breaker mechanism is almost completely sealed, and only the low-pressure oil tank has a respirator connected with the outside air. When the mechanism is in normal operation, the nitrogen in the nitrogen storage bottle is compressed by high-pressure oil through the piston of the pressure storage cylinder, and there is a high pressure. There is a sealing isolation between the compressed nitrogen and the high-pressure oil. During long-term operation, a small amount of nitrogen enters the high-pressure oil through the gap of the sealing ring. Under high oil pressure, the nitrogen is liquid. If the oil pump has not been pressurized for a long time to compensate for the decline of high-pressure oil pressure caused by the operation of the circuit breaker or the leakage of the oil pipe at the high-pressure side, these liquefied nitrogen will accumulate in the high-pressure oil and cannot be diffused to the low-pressure oil tank and discharged through the respirator. When the pressure relief valve is opened for manual pressure relief, the high-pressure oil is reduced to atmospheric oil in the hydraulic pump box, and the liquid nitrogen accumulated in the high-pressure oil becomes gaseous due to the sudden drop in pressure, forming nitrogen bubbles. These bubbles combine with each other to form nitrogen and accumulate in the hydraulic pump box and low-pressure oil pipe, while the low-pressure oil pipe has a U-shaped section, and the hydraulic oil accumulated in the U-shaped section makes nitrogen