Large-scale construction of UHV projects, core equipment is the key. In order to promote the further development of UHV AC transmission technology, the latest technological developments of key equipment such as UHV AC transformers, gas insulated metal-enclosed switchgear (GIS), series compensation devices and lightning arresters are summarized and forecasted. The results show that the UHV transformer should select the allowable value of the electric field strength when the partial discharge probability is 1‰ as the allowable field strength; the magnetic shielding at the end of the body, the electric shield of the tank, the magnetic shielding of the tank, and the magnetic leakage of the non-magnetic steel plate. The control measures can effectively reduce the leakage magnetic flux and temperature rise of the 1500MVA large-capacity UHV transformer; the breaking capacity of the UHV circuit breaker can reach 63kA, and the synthetic test circuit based on the “three-loop method†can break the test equipment limit and complete the 1100kV open circuit. The breaking test is carried out; it is clarified that the amplitude and frequency of the VFTO are limited by installing a damping resistor on the static contact side of the "vertical" isolating switch; it is proposed that the rated voltage of the UHV arrester is reduced to 780 kV from the viewpoint of continuous operating voltage. It is safe. Future UHV AC transmission and transformation equipment should be studied in depth in terms of high reliability, large capacity, new working principle and optimization of performance parameters.
UHV AC transformers, switchgear, series compensation devices and lightning arresters are the main core equipments of UHV AC transmission projects. This time, we will focus on the latest technical developments of these four types of equipment.
Development of UHV gas insulated metal-enclosed switchgear
China's UHV substations use UHV GIS, which consists of circuit breakers, disconnectors, grounding switches, current transformers and busbars. In the early stage, domestic manufacturing enterprises and foreign companies cooperated in the research and development of UHV GIS. The rated short-circuit breaking current was 50kA. In 2009, the Jindongnan-Nanyang-Jingmen UHV AC test demonstration project was successfully put into operation. After 2011, the country began to work on the localization and technical upgrading of UHV GIS, and developed a product with a short-circuit breaking capacity of 63kA, and invested in the expansion project of the UHV AC test demonstration project. Subsequently, the localization of UHV circuit breaker operating mechanism, basin type and supporting insulator was realized, which was widely applied in the transmission of power transmission from East to East and Zhe Ford high-voltage AC transmission project, and the technical parameters reached the international leading level.
In the development of UHV GIS, the development of UHV circuit breakers, isolating switches, basin insulators, etc., as well as large short-circuit current interruption, ultra-fast transient over-voltage (VFTO) suppression and high insulation design are key challenges. Introduce separately.
1. UHV circuit breaker
The voltage of the UHV circuit breaker is high, the short-circuit breaking current is large, the DC component decay time constant is 120ms, and the breaking is difficult. It is necessary to establish a test circuit equivalent to the actual breaking condition, which puts forward higher requirements for the breaking test and needs to be carried out. Insulation, short-circuit breaking and test technology research. In-depth research on the insulation performance, breaking capacity and test technology of the circuit breaker has been carried out in China, and an ultra-high voltage circuit breaker with double-break/four-break and 63kA breaking capacity has been developed.
1) Insulation performance
According to the internal structure of the circuit breaker, combined with different dielectric constants of SF6, epoxy resin and ceramics, an electric field simulation model was established, and the insulation characteristics were analyzed and calculated, as shown in Fig. 6. The arc-break chamber fracture is calculated by applying a 2400kV lightning impulse voltage to one end and applying a power-frequency voltage with a reverse polarity peak of 635kV at the other end, that is, 900kV, which is the most demanding condition. The product structure is optimized according to the electric field requirements, and the test verification meets the insulation requirements.
2) breaking ability
On the basis of the breaking capacity 50kA circuit breaker, the structure of the arc extinguishing chamber is optimized. Considering the effects of the opening speed, the volume of the compressor chamber, the shape of the nozzle and the breaking current, the gas pressure in the process of breaking the 63kA short circuit current of the circuit breaker is simulated and analyzed. The pressure distribution is shown in Figure 7. The pressure chamber and the nozzle A higher, ideal air pressure is obtained. Through the performance verification test conducted by the circuit breaker prototype, the parameters such as opening speed, arcing time, arcing interval and pre-breakdown time were improved. The type test results show that the developed UHV circuit breaker has superior large short-circuit current breaking capability.
3) Operating mechanism UHV circuit breaker adopts high-power hydraulic operating mechanism, which puts high requirements on operating characteristics and stability. On the basis of the hydraulic mechanism of the UHV circuit breaker with a breaking capacity of 50kA, according to the modular design, the output power of the mechanism is increased, and the high-flow quick-acting valve, the integrated multi-stage buffer system, and the sealing structure in the form of grid ring and seal are used. By optimizing various structural parameters, excellent mechanical properties are obtained, and the operating speed is adjustable.
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