A neutral grounding mode conversion device

Abstract

The invention discloses a neutral point grounding mode conversion device, which is characterized in that a controllable impedance is arranged between the neutral point of a power network and ground, and the impedance value of the controllable impedance is adjusted according to the open triangle voltage of a voltage transformer in the power network and / or the three-phase voltage of the power network with respect to ground, and the symmetry of the three-phase voltage of the power network is not changed; the controllable impedance is adjusted to make the power network be grounded with large current in normal operation state; the small current grounding mode or to large current grounding mode in single-phase grounding fault state can be converted; The neutral grounding mode can be converted between normal and single-phase grounding faults. The invention has the advantages of both large-current grounding and small-current grounding, and overcomes the disadvantages of different grounding modes, so that the overvoltage inside the power network is low, the trip rate is low, and the power supply reliability is high.

Description

technical field [0001] The invention relates to electric power equipment, more specifically, provides a neutral point grounding mode conversion device for a power transmission and distribution network, and realizes the mutual conversion of two or more neutral point grounding modes in a power grid. Background technique [0002] The electrical connection between the neutral point of the three-phase AC power system and the earth is called the grid neutral point grounding method. The neutral point grounding method involves the safety, reliability and economy of the power grid; at the same time, it directly affects the selection of insulation level of system equipment, overvoltage level, relay protection mode, communication interference, etc. Generally speaking, the neutral point grounding method of the power grid is also the neutral point grounding method of the voltage transformers at all levels in the substation. [0003] Neutral point effective grounding is high-current grou...

AI Technical Summary

Problems solved by technology

The advantage of the neutral point effective grounding method is that its internal overvoltage is low, the fault point is easy to locate, and the fault line can be quickly removed; its disadvantage is that because of the rapid removal of the fault line, the intermittent power supply leads to a high tripping rate and low power supply reliability. ; Moreover, the ground current is large, the ground potential rises higher, and the contact voltage and step voltage are increased; the interference to the information system is increased; the low-voltage network counterattack is increased

The advantages of non-effective neutral grounding are: single-phase grounding fault steady-state power frequency current is small; lightning insulation flashover instantaneous fault can be automatically cleared without tripping; single-phase grounding operation can improve the uninterrupted power supply of the grid and improve the reliability of power supply The grounding current is small, which reduces the rise of the ground potential, reduces the step voltage, reduces the interference to the information system, and reduces the counterattack to the low-voltage network, etc.; the disadvantage is: the internal overvoltage is high, and the weak The probability of insulation breakdown is high; the fault point is difficult to locate, and there is no line selection device that can select lines 100% accurately

In this mode of operation, lightning strikes, single-phase grounding short-circuit faults, etc. will cause overvoltage at the neutral point, and most of the transformers are graded insulation, so the overvoltage poses a great threat to the insulation of the neutral point. The treatment measure is to install a gap between the neutral point of the transformer and the ground and connect it in parallel with the lightning arrester. The discrete value of the gap breakdown voltage is very large, and the gap breakdown itself causes a sharp drop in the neutral point voltage. Neutral point insulation also causes impact

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