CN111030061A

CN111030061A - Main protection and backup protection strategy applicable to direct-current power grid

Info

Publication number: CN111030061A
Application number: CN201911241197.7A
Authority: CN
Inventors: 许建中; 武董一; 李嘉龙
Original assignee: North China Electric Power University
Current assignee: North China Electric Power University
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2020-04-17

Abstract

The invention relates to a main protection and backup protection strategy suitable for a direct current power grid, belonging to the technical field of multi-terminal direct current and direct current power grids; for a one-way circuit breaker, after a line fails, a main protection acts to remove the fault preferentially; the main protection refuses to operate, the circuit breaker on the outlet side of the converter station of the non-fault line operates, and the backup protection removes the fault, so that the method has certain engineering value.

Description

Main protection and backup protection strategy applicable to direct-current power grid

Technical Field

The invention relates to a main protection and backup protection strategy suitable for a direct current power grid, and belongs to the field of multi-terminal direct current and direct current power grids.

Background

With the increasing exhaustion of fossil resources in the world, the development of renewable energy sources is overwhelmed, and the flexible direct current power grid is rapidly developed. The flexible direct current transmission is a new generation of power transmission technology based on a fully-controlled power electronic device, and a direct current power grid based on the flexible direct current transmission can better realize wide-area complementary transmission of large-scale renewable energy sources, so that the flexible direct current transmission is one of important directions for development and revolution of the power grid in the future. At present, the Zhang Bei engineering and the Wudongde engineering under construction in China are symbolic engineering of direct current transmission, and future direct current power grid engineering is developed towards more terminals, larger capacity and higher reliability by taking the Zhang Bei engineering and the Wudongde engineering as starting points.

The modular multilevel converter topological structure is suitable for high-voltage high-power direct-current transmission occasions. In a high-voltage long-distance high-power direct-current transmission project, an overhead line has obvious economy, but the direct-current side fault rate is high, and a half-bridge sub-module does not have direct-current fault clearing capacity. If short-circuit fault occurs, the fault current can be rapidly increased to dozens of times of rated current, and a direct-current circuit breaker needs to be adopted to rapidly act to isolate a fault line, remove the fault current and improve the reliability of the system. Through the quick separation and combination of the circuit breakers, the quick isolation, the removal and the system recovery of a fault circuit are realized, the diffusion range of the fault can be reduced to the maximum extent, and the continuous and reliable operation of the system is ensured.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a main protection and backup protection strategy.

The technical scheme adopted by the invention is as follows: the main protection action on the outlet side of the converter station where the fault line is located is preferentially adopted in the fault loop, and if the one-way circuit breaker on the outlet side fails to operate, the backup protection action on the outlet side of the adjacent converter station cuts off the fault line; and the installation method of four bipolar circuit breakers is designed in the two-end converter station.

Compared with the prior art, the invention has the advantages that:

1. when a bipolar short-circuit fault occurs, a one-way circuit breaker is used for breaking to serve as protection, main protection action is preferentially carried out on the outlet side of a converter station where a fault line side is located, and fault current is quickly cut off;

2. and a matched backup protection strategy design is carried out, and after the main protection refuses to act, the backup protection acts to reduce the fault diffusion range to the maximum extent, so that the fault protection system has a complete fault protection system and can meet the fault clearing requirement under the conditions of complex faults and various systems.

Drawings

The invention is further described below with reference to the accompanying drawings.

FIG. 1 is a setting of primary and backup protection;

FIG. 2 is a schematic diagram of a main protection action when no rejection occurs;

FIG. 3 is a schematic diagram of backup protection action after a rejection occurs;

FIG. 4 is a schematic diagram of backup protection action after a secondary rejection occurs.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

The arrangement condition of the one-way circuit breaker applied to the main backup and the auxiliary backup of the four-terminal direct-current power grid is shown in fig. 1, wherein the main backup is represented by a one-way arrow, and the starting point of the arrow is the main backup; the secondary backups are represented by double-headed arrows, with the two sides of the arrow serving as secondary backups for each other. The direct current breaker adopting the unidirectional breaking is not in a single direction of breaking fixation, but in a reverse fault current direction, and is different from the unidirectional breaking in the traditional sense, so that the fault clearing range cannot be expanded under most conditions.

As shown in fig. 2, when a double short circuit fault occurs between the converter stations a and B (referred to as "near-end converter station" and the rest as "far-end converter station"), the double short circuit fault can be effectively disconnected when the "reverse fault current" is generated, i.e. the direction of the arrow is opposite to the direction of the fault current. Under the condition that no refusing occurs, both A2 and B2 act, and the fault isolation range is a line and is consistent with a bidirectional breaker.

As shown in fig. 3, in the case of one-time rejection, taking a2 rejection as an example, two breakers a1 and C1 are provided on the non-fault side line of the near-end converter station a, and depending on the current direction, C1 serves as a first backup.

As shown in fig. 4, when the rejection occurs twice, if C1 rejects again, C4 or D4 is used as a backup, and it is uncertain which breaker to break the circuit because the current direction between the far-end converter stations is uncertain during the fault. In the event of two rejections, the clearing range is three lines and two converter stations.

As can be seen from the above detailed description, in the field of high-voltage direct-current power transmission, the unidirectional direct-current circuit breaker can quickly isolate a fault line by coordinating main protection and backup protection, remove fault current, improve the reliability of a system, and ensure continuous and reliable operation of the system.

Finally, it should be noted that: the described embodiments are only some embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims

1. The utility model provides a main protection and back-up protection tactics suitable for direct current electric wire netting which characterized in that: the protection relies on the reliable action of a one-way circuit breaker to break the faulty line.

2. The primary protection strategy of claim 1, wherein: a fault occurs in the line between the two stations and the breaker on the outlet side of the station breaks the faulty line, preventing the fault from further developing.

3. A backup protection strategy according to claim 1, characterized in that: and if the main protection fails, the fault is expanded, and the circuit breakers of the adjacent converter stations cut off the roadblock line so as to meet the fault clearing requirement.

4. The primary protection and backup protection strategy of claim 1, wherein: PSCAD simulation software is adopted for simulation, and the strategy is reliable and effective.