Adaptive fault component current differential protection method based on current sag detection

Abstract

The invention relates to an adaptive fault component current differential protection method based on current sag detection, the steps of which are as follows: setting the parameters of the adaptive fault component current differential protection criterion, including the criterion adaptive adjustment start-up setting coefficient and Criterion Adaptive Ratio Brake Coefficient; collect the current injected from the DC system into the AC system on the inverter side in the high-voltage AC-DC interconnection system; judge the current amplitude Im in the single-phase virtual αβ coordinate system and the protection adaptive adjustment start-up setting threshold Adjust the ratio braking coefficient; judge whether the AC line on the inverter side of the high-voltage AC-DC interconnection system has an internal fault.

Description

technical field [0001] The invention relates to the field of control and protection of high-voltage AC-DC interconnected power grids in electric power systems, in particular to an AC line adaptive fault component current differential protection method based on current sag detection. Background technique [0002] The reverse distribution characteristics of my country's power generation resources and electricity demand determine my country's demand for cross-regional, long-distance and large-scale power transmission technology, and also promote my country's "west-to-east power transmission, north-south mutual supply, and national networking" power transmission pattern formation. High voltage direct and alternating current (HVDC / AC) interconnection grid has large transmission capacity and low construction cost, so it is widely used in long-distance power transmission and inter-regional grid connection. For the AC system lines of the high-voltage AC-DC interconnected grid, the f...

AI Technical Summary

Problems solved by technology

[0003] In the high-voltage AC-DC interconnected power grid, the regulation of the DC system caused by the fault of the AC system, especially the commutation failure of the DC system caused by the fault of the AC line on the inverter side, will cause the AC system to present the characteristics of complex faults, which will further affect the traditional AC protection. Adaptability in high-voltage AC-DC interconnection grids has an impact

When the AC system on the inverter side fails, the commutation bus voltage on the inverter side will drop to varying degrees, which will lead to commutation failure in the DC system, and even cause the DC system to be blocked and power transmission to be interrupted in severe cases.

In order to prevent the commutation failure of the DC system, the DC control system of the high-voltage AC-DC interconnected grid will quickly and nonlinearly adjust the current of the DC system after the fault and the current injected into the AC system of the inverter side to prevent the occurrence of commutation failure. It will affect the operating performance of the fault component current differential protection that operates instantaneously after the fault, and may cause the sensitivity of the fault component current differential protection to decrease or even refuse to operate when the AC line on the inverter side has an internal fault.

As the main protection of high-voltage AC lines, the degradation of fault component current differential protection action performance will lead to further expansion of AC system faults, and even have an impact on the stable operation of high-voltage AC-DC interconnected power grids

[0004] In view of the lack of adaptability of the main protection of the AC line on the inverter side of the high-voltage AC-DC interconnected grid, domestic and foreign scholars have carried out corresponding research

"Influence of HVDC Commutation Failure on Directional Comparison Pilot Protection of AC System" pointed out through protection misoperation examples that the failure of the AC system on the inverter side of the high-voltage AC-DC interconnected grid will cause the voltage drop of the commutation bus on the inverter side, which in turn will cause commutation on the inverter side. The commutation failure of the valve causes the action performance of the longitudinal differential protection device of the AC line to decline

"Research on the Application of Pilot Protection Based on Parameter Identification in AC-DC Hybrid Power Grid" combined with the simulation phenomenon pointed out that after the AC system on the inverter side of the high-voltage AC-DC interconnected grid fails, the fault evolution process and the electrical quantity presented during the fault period The characteristics are different from the pure AC system, which will lead to the phenomenon that the sensitivity of the AC line fault component current differential protection on the inverter side decreases or even refuses to operate when there is an internal fault.

Based on this, this document proposes a longitudinal protection principle suitable for parameter identification of long AC lines indirectly connected to the DC system. The performance of this protection principle is related to the length of the AC line. When the main protection of the AC line, the proposed method will have insufficient quickness and sensitivity

"HVDC commutation failure transient characteristics and its impact on differential protection analysis and countermeasures" uses the current amplitude ratio of the protection at both ends of the AC line on the inverter side to form a new current differential protection principle. This method solves the problem of The original fault component current differential protection has insufficient sensitivity or refusal to operate when the AC line on the inverter side has an internal fault. However, the operating performance of the proposed principle is easily affected by the selection of parameters. If the AC line on the failed inverter side is faulty, using this protection method will easily cause the non-faulty phase protection to malfunction and lead to further expansion of the fault.

The above research provides ideas for the adaptability analysis and improvement of the main protection of the AC line in the high-voltage AC-DC interconnection system. Less feasible in engineering

Images