CN-115347538-B - Method and device for isolating grounding faults of bipolar direct current system valve

CN115347538BCN 115347538 BCN115347538 BCN 115347538BCN-115347538-B

Abstract

The invention provides a method and a device for isolating a grounding fault of a valve of a bipolar direct current system, and relates to the technical field of high-voltage direct current transmission fault treatment; the method comprises the steps of starting differential protection for a valve side area when a grounding fault is detected on the valve side of a bipolar direct current system converter transformer, closing a fault pole converter valve, controlling a first alternating current breaker of a fault pole to be disconnected, controlling a second alternating current breaker of the fault pole to be disconnected after a delay preset time length so as to isolate the alternating current system from the fault point, and controlling the first switch and the second switch to be disconnected when direct current is smaller than a preset direct current threshold value so as to isolate the direct current system from the fault point. The invention can delay to trip two AC circuit breakers, does not need to judge whether the fault phase and the AC phase current have zero crossing points, and can rapidly finish the isolation of the grounding fault of the valve.

Inventors

WANG HAO
REN JUNHUI
WANG SHUAI
WANG JIEFENG
YANG FAN
CAO PENG
SONG ZHISHUN

Assignees

西安西电电力系统有限公司
中国西电电气股份有限公司

Dates

Publication Date: 20260505
Application Date: 20220913

Claims (8)

1. A fault isolation method for a valve side of a bipolar direct current system comprises a first direct current pole, a second direct current pole, a grounding unit and two groups of alternating current circuit breakers, wherein each group of alternating current circuit breakers comprises a first alternating current circuit breaker and a second alternating current circuit breaker, one end of the first direct current pole is electrically connected with a positive pole through a first switch, one end of the second direct current pole is electrically connected with a negative pole through a second switch, the other end of the first direct current pole and the other end of the second direct current pole are respectively electrically connected with the alternating current system through one group or a plurality of groups of alternating current circuit breakers, and the first direct current pole and the second direct current pole are grounded through the grounding unit, and the method comprises the following steps: when the grounding fault of the valve side of the bipolar direct current system converter transformer is detected, starting differential protection on the valve side area until the alternating current system is isolated from a fault point; Closing a fault pole converter valve, controlling a first alternating current breaker of a fault pole to be disconnected, and controlling a second alternating current breaker of the fault pole to be disconnected after delaying for a preset time length to isolate an alternating current system from a fault point, wherein the preset time length is set within 200ms according to actual requirements; when the direct current is smaller than a preset direct current threshold, the first switch and the second switch are controlled to be disconnected so as to complete the isolation of the direct current system from the fault point, wherein the preset direct current threshold is set to be 30A according to actual requirements; The method for determining the grounding fault of the valve side of the bipolar direct current system according to the valve side current of the converter transformer, the upper bridge arm current of the converter bridge, the lower bridge arm current of the converter bridge and the preset rated value comprises the steps of judging whether the following formula is established, and if so, determining the grounding fault of the valve side of the bipolar direct current system: Ivx-Ipx-Inx>k×IvAN wherein Iv is the valve side current of the converter transformer, ip is the upper bridge arm current of the converter bridge, in is the lower bridge arm current of the converter bridge, k is the protection fixed value proportionality coefficient, and x is the angle sign of a certain phase.
2. The method of claim 1, wherein the first dc pole comprises one or more MMC converter cells or diode rectifier bridge converter cells and the second dc pole comprises one or more MMC converter cells or diode rectifier bridge converter cells.
3. The method of claim 2, wherein the step of determining the position of the substrate comprises, The MMC converter unit at least comprises a starting resistor, a converter transformer, a converter valve and a converter reactor, wherein the converter valve and the converter reactor adopt a half-bridge topological structure, and the diode rectifier bridge converter unit at least comprises the converter transformer, the converter valve and the smoothing reactor.
4. The method of claim 3, wherein the step of, The neutral point of the converter transformer network side is grounded through a lightning arrester or directly grounded.
5. A method according to any one of claims 1-3, characterized in that the arcing duration of the first and second ac circuit breakers is not less than a preset duration threshold and that the first and second ac circuit breakers are ac circuit breakers having the capability to open half-wave short circuit currents.
6. A bipolar dc system valve side grounding fault isolation apparatus for performing the method of claim 1, wherein the bipolar dc system comprises a first dc pole, a second dc pole, a grounding unit, and two sets of ac circuit breakers, each set of ac circuit breakers comprising a first ac circuit breaker and a second ac circuit breaker, one end of the first dc pole being electrically connected to a positive pole through a first switch, one end of the second dc pole being electrically connected to a negative pole through a second switch, the other end of the first dc pole and the other end of the second dc pole being electrically connected to the ac system through one or more sets of ac circuit breakers, respectively, the first dc pole and the second dc pole being grounded through the grounding unit, the apparatus comprising: The protection module is used for starting differential protection on a valve side area until an alternating current system is isolated from a fault point when the grounding fault of the valve side of the bipolar direct current system converter transformer is detected; The alternating-current control module is used for locking the fault pole converter valve, controlling the first alternating-current breaker of the fault pole to be disconnected, and controlling the second alternating-current breaker of the fault pole to be disconnected after delaying for a preset time length so as to realize the isolation between an alternating-current system and a fault point, wherein the preset time length is set within 200ms according to actual requirements; And the direct current control module is used for controlling the first switch and the second switch to be disconnected when the direct current is smaller than a preset direct current threshold value so as to finish the isolation between the direct current system and the fault point, and the preset direct current threshold value is set to be 30A according to actual requirements.
7. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the bipolar dc system valve side ground fault isolation method of any one of claims 1 to 5 when the computer program is executed.
8. A computer readable storage medium, characterized in that the computer readable storage medium stores a computer program which, when executed by a processor, implements the bipolar direct current system valve side ground fault isolation method of any one of claims 1 to 5.

Description

Method and device for isolating grounding faults of bipolar direct current system valve Technical Field The invention relates to the technical field of high-voltage direct-current transmission fault treatment, in particular to a method and a device for isolating a grounding fault of a bipolar direct-current system valve. Background This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. The description herein is not admitted to be prior art by inclusion in this section. The direct current system adopting the symmetrical bipolar wiring has the advantages of being flexible in operation mode, capable of reducing rated operation voltage and the like, and is widely applied to high-voltage high-capacity direct current transmission systems. In recent years, flexible direct current systems based on Modular Multilevel Converters (MMCs) are widely applied to the aspect of large-scale centralized access of new energy due to the technical advantages of flexible power control, small harmonic content of output voltage and current, high modularization degree and the like. Meanwhile, the uncontrolled rectifier based on the diode converter has application prospect in a large-scale sea wind delivery system due to low cost, small occupied area and low operation loss. When an asymmetric ground short circuit (single-phase or two-phase ground) occurs on the valve side of a direct current pole formed by connecting one or more MMC converters and an uncontrolled rectifier bridge in series, the direct current bias is generated by the alternating current due to the unidirectional conduction of the diodes in the converters, and in severe cases, no current zero crossing point exists in the alternating current, so that the isolation and the elimination of the faults are difficult. Disclosure of Invention The invention provides a method and a device for isolating a grounding fault of a valve side of a bipolar direct current system, which can quickly and reliably isolate the grounding fault of the valve side area of a converter transformer. In a first aspect, an embodiment of the invention provides a valve side grounding fault isolation method of a bipolar direct current system, the bipolar direct current system comprises a first direct current pole, a second direct current pole, a grounding unit and two groups of alternating current circuit breakers, each group of alternating current circuit breakers comprises a first alternating current circuit breaker and a second alternating current circuit breaker, one end of the first direct current pole is electrically connected with a positive electrode through a first switch, one end of the second direct current pole is electrically connected with a negative electrode through a second switch, the other end of the first direct current pole and the other end of the second direct current pole are respectively electrically connected with an alternating current system through one group or more groups of alternating current circuit breakers, and the first direct current pole and the second direct current pole are grounded through the grounding unit, and the method comprises the following steps: when the grounding fault of the valve side of the bipolar direct current system converter transformer is detected, starting differential protection on the valve side area until the alternating current system is isolated from a fault point; closing a fault pole converter valve, controlling a first alternating current breaker of a fault pole to be disconnected, and controlling a second alternating current breaker of the fault pole to be disconnected after a preset time delay so as to isolate an alternating current system from a fault point; And when the direct current is smaller than a preset direct current threshold value, the first switch and the second switch are controlled to be disconnected so as to complete the isolation of the direct current system from the fault point. In a second aspect, the embodiment of the invention further provides a valve side grounding fault isolation device of a bipolar direct current system, the bipolar direct current system comprises a first direct current pole, a second direct current pole, a grounding unit and two groups of alternating current circuit breakers, each group of alternating current circuit breakers comprises a first alternating current circuit breaker and a second alternating current circuit breaker, one end of the first direct current pole is electrically connected with a positive electrode through a first switch, one end of the second direct current pole is electrically connected with a negative electrode through a second switch, the other end of the first direct current pole and the other end of the second direct current pole are respectively electrically connected with an alternating current system through one group or more groups of alternating current circuit breakers, and the first direc