| 操作过电压 |
| 添加时间：2018/10/20 10:06:25 浏览次数： |
| 在6～35 kV的中性点非直接接地系统中，当进行负载的起动或停止操作或发生事故时，由于开关触头间电弧重燃，运行状态发生突变，引起电容和电感元件之间电磁能量相互转换，出现一种振荡性过电压，即产生操作过电压。 In 6-35 kV neutral point indirectly grounded system, when starting or stopping operation of load or accident occurs, the arc between switching contacts is re-ignited and the operation state is abruptly changed, which results in the electromagnetic energy conversion between capacitor and inductor, and an oscillatory overvoltage, i.e. switching overvoltage, occurs. (1)电动机起动合闸过电压 (1) starting overvoltage of motor starting 理论上认为，电动机合闸起动时，电动机机端产生的过电压为式中， ；为合闸电压瞬时值；z；为电动机冲击波阻抗；Z 为电缆冲击波阻抗。一般地，Z=100～5000Q，z =20～50 Q，因此电动机合闸起动时，电动机机端产生的过电压可达2倍相电压。对于真空开关，触头闭合前往往会发生预击穿，电弧的燃弧和熄灭可达数十次，这种预燃过电压幅值较大且波前很陡，对电动机的绝缘可造成较大的威胁,电机产生过电压可装设电机型过电压保护器。 Theoretically, it is considered that the over-voltage at the motor end is the type of neutral, the instantaneous value of the switching voltage, the impulse impedance of the motor, and the impulse impedance of the cable. Generally, Z = 100-5000Q, z = 20-50Q, so when the motor is turned on and started, the overvoltage generated by the motor end can reach twice the phase voltage. For the vacuum switch, the contact closing will occur pre-breakdown, arc ignition and extinguishing can be up to dozens of times. This pre-ignition overvoltage amplitude is large and the wavefront is very steep, which can cause a greater threat to the insulation of the motor. Motor overvoltage can be installed motor-type overvoltage protector. (2) 电动机起动状态分闸过电压 (2) switching overvoltage of motor starting state 运行经验表明，在断开感性负载时，由于感性电流不在零点就被迫截断即所谓的截流，造成开关触头间电弧燃烧很不稳定，波形产生高频振荡，在电感回路中产生的突变电流会感应出很高的电压。 Operation experience shows that when the inductive load is disconnected, the arc burning between the switch contacts is unstable because the inductive current is forced to be cut off when it is not at zero, and the waveform generates high frequency oscillation. The sudden change current in the inductive circuit will induce high voltage. 1)截流过电压由于真空断路器有良好的灭弧性能，当断开小电流时，真空电弧在过零前就熄灭。由于电流被突然切断，其滞留于电机等电感绕组中的能量必然向绕组的杂散电容充电，转变为电场能量。对于电机和变压器，特别是空载或容量小时，则相当于一个大的电感，且回路电容较小，因此会产生大的过电压。可以产生很高的过电压，但由于触头和回路中有一定的电阻产生损耗以及发生击穿，对过电压值有相当的抑制作用。但这种抑制作用是有限的，不能消除过电压。因此，特别是对电感负载在采用真空断路器作为操作元件时，应加装过电压保护器,过电压保护器型号有很多种,用户可根据自己的保护对象来选型。 1) Cut-off overvoltage because the vacuum circuit breaker has good arc extinguishing performance, when the small current is cut off, the vacuum arc will be extinguished before zero. Because the current is suddenly cut off, the energy which is trapped in the inductance winding such as the motor must be charged to the stray capacitor of the winding, and be converted to the electric field energy. For motor and transformer, especially no-load or small capacity, it is equivalent to a large inductance, and the loop capacitance is small, so it will produce a large overvoltage. High overvoltage can be generated, but due to contact and circuit resistance in a certain loss and breakdown, the value of overvoltage has a considerable inhibition. But this inhibition is limited and can not eliminate overvoltage. Therefore, especially when the vacuum circuit breaker is used as the operating element for inductance load, the overvoltage protector should be installed. There are many types of overvoltage protector, and users can choose the type according to their protection object. 2)三相同时断开过电压 2) three phase simultaneous interruption of overvoltage 三相同时断开过电压是由于断路器首先断开相弧隙产生重燃时，流过该相弧隙的高频电流引起其余两相弧隙中的工频电流迅速过零，致使未开断相随之被切断，在其余两相弧隙中产生类似较大水平的截流现象，从而产生更高的操作过电压。所产生的过电压是加在相与相之间的绝缘上。在开断中小容量电机或轻负载情况下容易出现三相开断过电压,所以要安装三相组合过电压保护器。 The three-phase simultaneous disconnection overvoltage is caused by the high-frequency current flowing through the phase gap when the circuit breaker first disconnects the phase gap and causes the power-frequency current in the remaining two-phase gap to cross zero rapidly, resulting in the disconnection of the unbroken phase and the occurrence of a similar large level of current interception in the remaining two-phase gap, resulting in a higher level of current interception. Operating overvoltage. The generated overvoltage is added to the insulation between the phase and the phase. Three-phase interrupting overvoltage is easy to occur when small and medium capacity motors or light loads are interrupted, so three-phase combined overvoltage protector should be installed. |
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