Comparison and function introduction of arc suppre

2022-07-25
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Summary: the harm of single-phase grounding capacitive current. In the high-voltage power supply where the neutral point is not grounded, the harm of single-phase grounding capacitive current is mainly reflected in the following four aspects

key words: comparison of current status of arc suppression coil introduction the harm of single-phase grounding capacitive current in ungrounded high-voltage power supply, the harm of single-phase grounding capacitive current is mainly reflected in the following four aspects: the harm of arc grounding overvoltage once the capacitive current is too large, the arc at the grounding point cannot be extinguished automatically. When intermittent arc grounding occurs, arc grounding overvoltage will be generated. This overvoltage can reach 3~5 times or higher than the phase voltage. It spreads throughout the whole electricity and lasts for a long time, up to several hours. It not only breaks through the weak insulation links in the electricity, but also does great harm to the whole insulation. Cause thermal damage to the grounding point and increase of the grounding voltage. The single-phase grounding capacitor current is too large, which increases the thermal effect of the grounding point and causes thermal damage to the cable and other equipment. After the current flows into the ground, due to the grounding resistance, the whole grounding voltage rises, endangering personal safety. AC stray current endangers the formation of stray current in the earth after the capacitive current flows into the earth. The current may produce sparks, ignite gas explosion, etc., which may cause the detonator to shoot in advance and corrode water pipes and gas pipes. The role of arc suppression coil in gas and coal dust explosion caused by grounding arc after installing arc suppression coil, when single-phase grounding occurs, the arc suppression coil generates inductive current, which compensates the capacitive current formed by single-phase grounding, reducing the grounding current, reducing the recovery voltage speed of fault phase, and controlling the harm caused by excessive capacitive current. At the same time, due to the embedded effect of arc suppression coil, it can effectively prevent the generation of ferroresonance overvoltage. The better the compensation effect of arc suppression coil is, the greater the safety protection effect on electricity is. Therefore, it is necessary to track the change of capacitive current and automatically tune the arc suppression coil. The function principle of arc suppression coil and the current situation at home and abroad the function of arc suppression coil is to provide an inductive current to compensate the grounding capacitive current, reduce the grounding current, and reduce the recovery voltage speed at both ends of the fault phase grounding arc, so as to achieve the purpose of extinguishing the arc. When the arc suppression coil is properly tuned, it can not only effectively reduce the probability of arc grounding overvoltage, but also effectively suppress the radiation value of overvoltage. At the same time, it can also minimize the thermal damage at the fault point and the grounding voltage. The so-called correct tuning means that the inductive current is grounded or equal to the capacitive current. In engineering, the detuning degree V is used to describe the tuning degree v= (ic-il)/ic. When v=0, it is called full compensation, when v = 0, it is under compensation, and when v = 0, it is over compensation. From the point of view of the role of arc suppression coil, the smaller the absolute value of detuning degree, the better. It is best to be in the fully compensated state, that is, to be adjusted to the resonance point. However, during the normal operation of electricity, the arc suppression coil with small detuning degree will produce various resonant overvoltages. For example, for 6kV coal mine power, when the arc suppression coil is in the fully compensated state, the neutral point displacement voltage under the normal steady-state operation of the power is 10~25 times that of the uncompensated power, which is commonly referred to as the series resonance overvoltage. In addition, various electrical operations (such as the input of large motor, non synchronous closing of circuit breaker, etc.) may produce dangerous overvoltage. Therefore, during normal electrical operation or other faults other than single-phase grounding fault, the arc suppression coil with small detuning degree will not bring safety factors but harm to the electricity. To sum up, when there is no single-phase grounding fault, the greater the detuning degree of the arc suppression coil, the better. It is better to exit the operation. 3.1 classification of compensation system in the early stage, the arc suppression coil with manual turn adjustment and fixed compensation is called fixed compensation system. The working mode of the fixed compensation system is: set the arc suppression coil in the over compensation state, and the degree of over compensation depends on the fact that the neutral point displacement voltage does not exceed 15% of the phase voltage during the normal steady-state operation. The over compensation is used to avoid the dangerous series resonance over-voltage when some lines are electrically cut off. Because if the setting is under compensation, cutting off the line will reduce the capacitive current, and full compensation or near full compensation may occur. However, when the device operates in the over compensation state, the detuning degree cannot be controlled when the parameters such as accidental tripping or reclosing change in the power supply, so that it often operates under the disallowed detuning degree, resulting in the neutral point overvoltage and the destruction of the three-phase voltage symmetry. It can be seen that the fixed compensation method is difficult to adapt to the electricity with frequent changes, and this system is no longer used. Instead, it is a device that tracks the current of electric capacitance and automatically tunes. This kind of device is divided into two types, one is called follow-up compensation system. The new material announcement of the industrial new University of technology of the follow-up compensation system is: automatically track the change of the electric capacitor current, adjust the arc suppression coil at any time to keep it at the resonance point, string a resistance in the arc suppression coil, increase the resistance ratio, and limit the resonance overvoltage to the allowable range. When a single-phase grounding fault occurs, the control system will short-circuit the resistance to achieve the best compensation effect. The arc suppression line of the system is the main reason why the small panel control system is not widely used. The coil cannot be adjusted with high voltage. The other is called dynamic compensation system. The working mode of the dynamic compensation system is: when the electricity is in normal operation, adjust the arc suppression coil to be far away from the resonance point to completely avoid the possibility of series resonance overvoltage and various resonance overvoltage. When the electricity is grounded in single phase, adjust the arc suppression coil to the best state instantly to make the grounding arc extinguish automatically. This system requires that the arc suppression coil can be adjusted quickly with high voltage, which fundamentally avoids the possibility of series resonance. Through appropriate control, this system is the only system that can make the original power directional single-phase grounding line selection device continue to be used. 3.2 comparison of main domestic products at present, there are three types of arc suppression coil with automatic compensation in China, namely, air gap adjustment type, turn adjustment type and magnetic bias type. Air gap adjustment air gap adjustment belongs to the follow-up compensation system. The arc suppression coil belongs to the moving core structure, which can continuously adjust the inductance in 2017 by moving the iron core to change the magnetic circuit reluctance. However, the adjustment can only be carried out under low voltage or no voltage, and the ratio of the upper and lower limits of the inductance adjustment range is 2.5 times. Adjust the arc suppression coil under normal electrical operation of the control system

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