A current differential protection method for flexible DC lines based on energy frequency bands

Abstract

The invention discloses a flexible DC line current differential protection method based on an energy frequency band. The method is characterized by comprising steps that step 1, current sensors are respectively arranged at breaker portions at two ends of a DC line; step 2, protection devices are respectively arranged at the two current sensors, an opposite-end current instant value of the DC line is acquired through fiber communication between the protection devices, and a differential current instant value is calculated; step 3, a protection start criteria formula is formed according to amplitude of current change amount after a fault, when the start criteria is satisfied, the process enters a step 4; step 4, according to a bipolar fault criteria formula, whether a system is in a bipolar short circuit fault is determined, if yes, the process enters a step 5; and step 5, according to an in-area fault criteria formula, whether the fault is a present line in-area fault is determined, if yes, protection outlet tripping is carried out.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a method for current differential protection of a flexible DC line based on an energy frequency band. Background technique [0002] With the development of voltage source converter (voltage sourced converter, VSC) and the increase of DC link in the current conversion of power supply and load, the flexible DC system has the advantages of flexible control, easy acceptance of distributed power supply and DC load, and large power supply capacity. , good power quality and other advantages have attracted widespread attention at home and abroad. However, the lack of mature DC line protection technology is one of the main challenges faced by flexible DC systems. The difficulty of line protection for flexible DC systems is to quickly identify DC faults in a short time to prevent equipment damage, and to accurately select fault lines to reduce the scope of p...

AI Technical Summary

Problems solved by technology

[0004] 1. It is difficult to achieve a clear protection boundary for single-ended quantity protection, and cannot better meet the rapidity and selectivity requirements of flexible DC line protection

[0005] 2. Directional longitudinal protection is mainly based on the current mutation to determine the current direction. However, after a fault, the VSC quickly locks up, and the system topology changes fundamentally. The superposition principle will no longer apply

[0006] 3. Directional longitudinal protection based on sudden change in current is not suitable for flexible DC systems in principle

[0007] 4. The principle of current differential protection is simple and reliable, but DC line current differential protection is easily affected by the transient current of line distributed capacitance

If the setting value of the current differential protection is too low, the transient current of the distributed capacitance of the line in the event of an external fault will easily cause the protection to malfunction, and the reliability of the protection is difficult to meet; movement, the sensitivity of the protection is difficult to meet

[0008] Therefore, it is hoped that there is a flexible DC line current differential protection method that can overcome or at least alleviate the problem that the DC differential protection in the prior art is susceptible to the transient current of distributed capacitance.

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