A distance protection method by identifying overload and fault in a transmission line

Abstract

The invention relates to a distance protection method by identifying overload and fault in a power transmission line, the distance protection includes phase-to-phase distance protection and grounding distance protection; Cosine component of positive sequence voltage, cosine component of line voltage and cosine component of phase voltage; determine the sudden change of cosine component of positive sequence voltage, cosine component of line voltage and cosine component of phase voltage at the place where the protection is installed after the transmission line distance protection is started; judging The fault type of the transmission line after the distance protection is activated. This method can be used as the opening condition of section III of the distance protection. When the opening condition is met and the measured impedance is within the distance protection action zone, the distance protection operates. In case of overload, reliable blocking distance protection. This method does not need to be set, and is realized inside the protection device of the transmission line.

Description

[0001] Technical field: [0002] The invention relates to a distance protection method for identifying loads and faults, and more particularly to a distance protection method for identifying overloads and faults in transmission lines. [0003] Background technique: [0004] In power system transmission lines, overload is a common abnormal operation state, which can be divided into normal overload and accident overload. Normal overload means that the line load exceeds the maximum load during normal operation; accidental overload means that one or more lines in the transmission section fail or trip without fault, resulting in power flow shifting and resulting in an increase in the power flow of other operating lines, exceeding the maximum load during normal operation. Load, also known as power flow transfer overload. Long-term overload or severe overload operation of the system will pose a serious threat to the safety of the power grid and equipment, and increase the risk of maj...

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Problems solved by technology

This also exposes the problem between relay protection and safety and stability control and dispatch: before the measures are taken or the measures take effect, the fast-acting relay protection has cut off the overload components, which further aggravates the power flow transfer and system oscillation

[0007] Analysis of overload characteristics and distance protection measures to deal with overload are generally based on the impedance plane, by analyzing the size of the load impedance, comparing the relative position between the load impedance and the action area of ​​the distance protection, artificially setting the load limit line (Gao Xu, Xu Guixian, Guo Dengfeng , Niu Siqing, Load limiting resistance setting method of heavy current line in North China Power Grid, Electric Power System Automation, 2007, 31(5): 94-96, 104) to prevent the distance protection from malfunctioning under overload conditions, but because the load is changing, As the load continues to increase and the load impedance decreases, it is still possible to enter the distance protection action area, causing distance protection malfunctions. On the other hand, when setting the fixed load limit line, consider the most serious overload of the system and weaken The operation performance of the distance protection is improved, especially the ability of the distance protection to withstand the transition resistance. When a high-resistance fault occurs under light load, the distance protection cannot operate, and the load limit line is artificially set, so there is a risk of missetting. The size has a great influence on the action performance of the protection. If the setting value is too large, the system will be overloaded, and the distance protection will easily malfunction. If the setting value is too small, the action performance of the distance protection will be affected.

During the development of a blackout accident, the power flow of the system shifts rapidly, and the load of the line increases rapidly, far exceeding the normal maximum load taken into account in the setting. Misoperation of the distance protection is inevitable, so the fixed load limit line cannot prevent the overload situation. Misoperation of distance protection, and the analysis of distance protection on the impedance plane has limitations in coping with overload strategies

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