Multi-terminal flexible DC power grid line direction pilot protection method

Abstract

The invention discloses a multi-terminal flexible DC power grid line direction pilot protection method. The method comprises steps: DC current and voltage at two ends of a DC reactor are measured and a DC current mutation rate di / dt and a voltage mutation rate du / dt are calculated; when the di / dt or the du / dt is larger than a threshold value K1-set and K2-set, a protection algorithm is started instantly; fault voltage at two sides of a DC reactor at a protection terminal is measured, and corresponding transient components UM_line and UM_bus (UN_line and UN_bus) are extracted; r1=UM_line / UM_bus (r2=UN_line / UN_bus) is calculated, and a fault direction is judged: if r1>1+epsilon (r2>1+epsilon), epsilon is a reliable margin, positive direction fault is judged and a direction signal RM is equal to 1 (RN=1), or otherwise, reverse direction fault is judged, and a direction signal RM is equal to 0 (RN=0); when RM&RN=1, internal fault is judged; and when RM&RN=0, external fault is judged. The method of the invention has the advantages that data synchronization is not needed; a sampling rate is lowly required; the fault resistance withstanding ability is strong; influences from line distributed capacitance do not exist; engineering implementation is facilitated; and the hardware investment cost is reduced.

Description

technical field [0001] The invention relates to the field of power system protection and control, in particular to a multi-terminal flexible direct current grid line direction longitudinal protection scheme based on the transient voltage amplitude ratio. Background technique [0002] As a very promising power transmission and distribution solution, flexible DC technology has the advantages of large power transmission capacity, long power transmission distance, flexible power regulation, narrow line corridors, and more convenient interconnection between power grids compared with AC power transmission. Therefore, it is very suitable for long-distance power transmission, distributed energy access, interconnection between asynchronous power grids, cable power supply in the center of large cities, and island power supply. [0003] DC line protection of flexible DC system is one of the key technologies in the development of flexible DC. The main difficulty of this technology lies...

AI Technical Summary

Problems solved by technology

[0007] Since the existing differential protection does not consider the capacitive current problem, any process that causes voltage changes, such as external faults and start-up processes, may cause malfunction. Therefore, in order to prevent malfunction, the criterion requires a long delay

Originally, the current differential protection should have the advantages of high sensitivity and fast action speed, but it is far from being used in DC transmission lines, and its performance needs to be improved urgently

Images