Suppression measures of resonant overvoltage in th

Suppression measures of medium voltage resonance overvoltage

the neutral point grounding mode of medium voltage (35kV, 10kV, 6kV) adopts the small current grounding through arc suppression coil for many years, but in recent years, some areas adopt the neutral point grounding mode through small resistance. The power supply reliability of the former is much higher than that of the latter, but there are also the following problems: when the system is grounded, due to the small residual current at the grounding point, the zero sequence overcurrent and zero sequence directional protection cannot detect the grounded fault line. During operation, it can't be adjusted in time according to the change of electric capacitance current, and the arc light can't self extinguish and overvoltage problems occur

China has developed and produced a microcomputer automatic tracking arc suppression device, which effectively solves the technical problem that the neutral point is grounded through the arc suppression coil for a long time. The Z-shaped structure grounding transformer of the device has small zero sequence impedance, low loss, and can carry secondary load; Microcomputer control unit is the core to realize automatic tracking detection, adjustment and line selection; The response time of the system is less than 20s, and there are three operation modes: over compensation, under compensation and minimum residual current. The grounding compensation device based on automatic tuning principle can better solve such problems through the operation modes of over compensation, full compensation and under compensation

at present, most of the new arc suppression coils adopt on load turn adjustment mode. The number of regulating taps is generally greater than 9. The on load switch works in the preset mode, and the arc suppression coil tuning is automatically controlled by the microcomputer controller. It is suggested that the old arc suppression coil that needs to be reformed at present should adopt a new type of automatic tuning arc suppression coil. The arc suppression coil adopts the on load turn adjustment mode, the normal operation adopts the over compensation mode, the grounding circuit of the arc suppression coil is connected with the damping resistance in series, and the control part adopts the microcomputer controlled automatic harmonic elimination device for automatic compensation; It can automatically detect the changes of the parameters of the electric capacitance to the ground, automatically and manually adjust the tap of the arc suppression coil to make it run at the best working point, and ensure that the residual current can be reduced to the extent of reliable arc extinguishing; It can also be remotely controlled, signaled, telemetered and adjusted to meet the needs of unattended substation

the limitation of ferroresonance overvoltage caused by the saturation of voltage transformer core must make the system parameters change greatly in order to suppress the resonance overvoltage. If the arc suppression coil is connected to the neutral point of the system to destroy its resonance condition, the green new material, the excitation reactance of Pt is relatively large (kilo ohm to megaohm level), while the inductance of arc suppression coil (100 ohm level) is relatively small, so the resonance condition l=1/C is difficult to meet, and the resonance will not occur. With the arc suppression coil, the capacitor discharges to the small inductive reactance, and the current in the PT is very small and will not be burned. Therefore, the arc suppression coil is also connected in the middle. For the ferromagnetism caused by the saturation of the iron core of the voltage transformer, the 1-liter Tetra Pak aseptic packaging with biological plastic and a 30mm lightweight cover has been sold worldwide. The resonance peraluminous ore and its concentrate have a good limiting effect on the increased contribution rate of 168% to the import voltage. The continuous improvement, popularization and application of automatic tracking arc suppression coil and grounding line selection device provide technical guarantee for the grounding of MV neutral point through arc suppression coil. Therefore, the neutral grounding through arc suppression coil is the development direction of medium voltage in China