Flexible grounding method for power distribution network through transformer

Abstract

The invention provides a flexible grounding method for a power distribution network through a transformer, and the method comprises the steps: connecting a primary side of the transformer to the power distribution network, and generating a neutral point; when a single-phase earth fault occurs, directly or externally adding any two phase lines on the secondary side of the transformer between the neutral point and the ground through a series variable impedance according to a fault phase selection result, so that the voltage of the neutral point can be flexibly regulated and controlled; enabling the voltage of the fault point to be lower than the voltage of continuous combustion of the grounding arc, forcing the fault point to extinguish arc, and monitoring the ground insulation parameters of the power distribution network to sense whether the grounding fault is eliminated; and for a permanent grounding fault, realizing fault continuous arc extinction or external in-phase voltage amplification fault positioning. According to the method provided by the invention, the neutral point of the system can be led out by only one transformer, the instantaneous single-phase grounding fault can be eliminated, and the permanent single-phase grounding fault voltage or grounding protection tripping can be inhibited.

Description

technical field [0001] The invention relates to the technical field of single-phase grounding fault suppression of distribution network, in particular to a method for flexible grounding of distribution network through a transformer. Background technique [0002] The 3-66kV medium-voltage distribution network extends to every corner of the world. Power lines run through forests, cities, underground, and mines. The operating environment is complex, and accidents such as high-voltage line drop, electric shock, and cable insulation discharge and fire are prone to occur. Globally, thousands of people are electrocuted every year due to distribution network failures, thousands of fires are caused by arc faults, and economic losses such as power outages are tens of billions of yuan. In recent years, in order to reduce the fault point current after a ground fault occurs in the distribution network, the neutral point of the 3-66kV distribution network at home and abroad usually adopts...

AI Technical Summary

Problems solved by technology

The neutral point ungrounded method is suitable for distribution networks with capacitive currents less than 10A. This grounding method can operate with a single-phase ground fault for 2 hours, which is conducive to improving the reliability of power supply. The length of cable laying is gradually increased, and the leakage current and capacitive current of the distribution network are also gradually increased, which is easy to cause intermittent arc overvoltage, and there is a risk of electric shock and fire

The grounding method through the arc suppression coil can promote instantaneous fault arc suppression and improve the reliability of power supply, but the arc suppression coil cannot compensate the active component and harmonic component of the fault current, and it is easy to generate intermittent arc overvoltage, the compensation effect is very limited, and there is permanent grounding Risk of electric shock and fire due to malfunction

The grounding method through a small resistance can only sense and cut off the grounding fault below 200Ω, which can effectively suppress the intermittent arc overvoltage, but it cannot suppress the instantaneous fault arc, which may cause the user to double the number of power outages, and drop the overhead line to the concrete floor Equal high-resistance ground fault protection is helpless, and there is a risk of electric shock and fire

[0003] In order to improve the shortcomings caused by the above-mentioned traditional grounding methods, some scholars have proposed a flexible grounding method based on power electronics technology, so that the active full compensation device can calculate and output a zero-sequence The current corresponding to the negative value of susceptance, through feedback adjustment, continuously corrects the injected current until the ground admittance of the fault feeder after the fault is equal to the value before the fault. The higher requirements of the current control and other links make it difficult to apply in the actual distribution network. On the other hand, due to the extensive use of power electronic devices, it is expensive and the domestic promotion is limited.

Some scholars have proposed the methods of neutral point resistance grounding leading phase inductance, neutral point reactance grounding lagging phase capacitance or leading phase inductance. Under the known conditions, but there is no mention of the grid-to-ground insulation parameter measurement and phase selection method, and the neutral point grounding impedance and the impedance value of the biasing element need to be adjusted at the same time. The operation is relatively complicated and the practical application is limited.

[0004] In 2017, the inventor proposed a safe operation method for step-down and arc suppression of the ground fault phase of the non-effectively grounded system (patent application number 201710544978.8). ground, or the neutral point and the ground plus a controllable voltage source to reduce the voltage of the fault phase, realize the voltage arc suppression and active step-down operation of the ground fault, can realize 100% arc suppression of instantaneous faults, and effectively avoid the non-fault phase The insulation is broken down, which solves the technical problems of poor arc suppression effect of traditional arc suppression methods and low reliability of traditional protection methods

However, this method requires the cooperation of the grounding transformer and the injection transformer, and the cost is relatively high. The failure of the injection transformer will cause the failure of the entire arc suppression method; the judgment of the disappearance of the fault requires accurate measurement of the conductance of the three phases, which is difficult in practical application and has low reliability; and Lack of isolation measures to cooperate with the feeder grounding protection device in the event of a permanent fault on the line

[0005] In short, the existing grounding methods cannot take into account the reliability and economy of single-phase ground fault suppression in the distribution network

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