Selection and analysis of the hottest combined ove

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Selection and analysis of combined overvoltage protector

1 introduction the combined overvoltage protector is a new type of overvoltage protection device, which is mainly used in 35kV and below power systems to limit lightning overvoltage, vacuum circuit breaker operating overvoltage and various transient overvoltages that may be close to the spraying effect in the power system. It can significantly underperform the market and effectively protect motors, transformers, switches The insulation of capacitor, cable, bus and other power equipment will not be damaged, and can reliably limit the overvoltage between phases and phase to ground. At present, the wide application of vacuum circuit breaker device makes people pay more and more attention to the harm caused by operating overvoltage. There are many types of combined overvoltage protectors, which makes us have a lot of space in application selection, but at the same time, it will make us choose more carefully. The purpose of this paper is to discuss the selection of combined overvoltage protector (combined zinc oxide arrester) in vacuum circuit breaker device. 2 the origin of the application of combined over-voltage protector the development of arrester products in China has gone through several stages: common valve arrester, magnetic blow arrester and metal oxide arrester (MOA). In recent years, the overall manufacturing level and quality of arresters have been greatly improved. With the wide application of vacuum circuit breaker, many measures have been taken to limit the over-voltage in order to limit its operating over-voltage and avoid the insulation damage of powered equipment. Generally, the protection devices for operating overvoltage of vacuum circuit breaker devices include the following categories: (1) resistance capacitance absorption devices; (2) Gapless zinc oxide arrester; (3) Zinc oxide arrester with series gap. The greatest advantage of the resistance capacitance absorption device is that it can ease the steepness of the overvoltage wave invading the protected equipment and improve the voltage gradient on the equipment winding. However, it has the problems of large volume, no obvious overvoltage limit, small absorbed overvoltage energy capacity, and high-order harmonic pollution. The gapless zinc oxide arrester is an advanced overvoltage protection equipment. Compared with the traditional silicon carbide arrester, it has excellent characteristics in terms of protection characteristics, making and breaking capacity and anti pollution. The nonlinearity of its ZnO Resistor is extremely excellent, which makes its close insulation under normal operation drop by 12.3% year-on-year From the overall view of this year. However, it can not meet the requirements of frequent operation under operating overvoltage due to its high protection residual voltage, and has the limitations of power frequency aging, bearing charge rate and thermal balance conditions, which is still insufficient for the protection of motor insulation and withstand voltage level equipment. Due to the increase of series gap of zinc oxide arrester with series gap, MOA can use a small number of ZnO resistors. At this time, the residual voltage can be very low. If the discharge voltage of spark gap is also very low, the arrester can not only have a very low protection level, but also avoid the deterioration and power loss caused by the large resistive component of leakage current. Compared with MOA without gap, MOA with series gap has higher ability to withstand system temporary overvoltage, can ensure its own safety in case of system grounding fault, and has lower lightning impulse discharge voltage and residual voltage level, which can provide good protection for equipment with weak insulation level, especially suitable for neutral point non effective grounding system. In recent years, China has developed a variety of three-phase combined zinc oxide surge arresters with series gap or without gap. They are connected with a certain proportion of ZnO Resistor or with spark gap between phases and phase to ground. They are a composite surge arrester. This overvoltage protection device has a good protection effect on phase to phase overvoltage. Because the combined overvoltage protector adopts composite insulation structure, it is less affected by the size of switch cabinet on installation, so it is increasingly recognized by people. 3 gap structure and characteristics of combined overvoltage protector combined overvoltage protector can be divided into two types: no gap and with series gap. This paper mainly discusses the zinc oxide arrester with series gap. The combined zinc oxide arrester is composed of a special gap body and a zinc oxide valve (ZnO). According to the manufacturer's technical scheme, the gap structure is also different. The gaps mainly include four gaps, three gaps, diamond gaps (single gap), six gaps, etc. at the same time, there are two kinds of gaps: parallel resistance and no parallel resistance. Different technical characteristics of clearance are also different. (1) The four gap star connection combined overvoltage protector consists of four identical protection units. Each unit is composed of discharge gap and ZnO Resistor. Its wiring schematic diagram is shown in Figure 1. In this protector, ZnO and discharge gap are combined to protect each other. The discharge gap makes the charging rate of ZnO zero, and the excellent nonlinearity of ZnO makes the discharge gap immediately extinguish the arc, no cut-off and no continuous current after the action. The discharge gap no longer undertakes the arc extinguishing task, and the impact coefficient can reach 1. The discharge voltage value does not change with the change of discharge waveform, so the service life is improved. This wiring method can greatly reduce the phase to phase overvoltage. Compared with the conventional MOA, the phase to phase overvoltage is reduced by 60% - 70%. It can operate safely for a long time under single-phase grounding, intermittent arc grounding and resonant overvoltage. As the phase, phase and ground are double gaps, each gap bears 1/2 of the power frequency discharge voltage. Under normal circumstances, the center point potential is "zero", so the power frequency voltage is borne by the phase gap. At the same time, there is parasitic capacitance to the ground, which will make the actual discharge value unstable. (2) The three gap star connection combined overvoltage protector consists of three gaps and four units, and its wiring schematic diagram is shown in Figure 2. The difference between its structure and the four gap is that the gap of the grounding protection unit is eliminated, the phase to ground protection adopts a single gap, the grounding protection unit is composed of pure resistive materials, and the central point is relatively small affected by external factors such as parasitic capacitance and stray capacitance. In case of phase to phase overvoltage, the tension and contraction of the phase to phase protection unit and the grounding protection sample are carried out separately (that is, the tension and contraction are carried out with different clamps) and the protection unit is jointly completed. The phase to phase overvoltage is also borne by two gaps. The phase to phase and phase to ground power frequency discharge voltage can be made the same through the adjustment of the grounding protection unit. (3) The rhombic gap star connection combined overvoltage protector consists of one rhombic gap and four units. Its wiring principle

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