Longitudinal traveling wave differential protection method suitable for symmetrical bipolar DC line

Abstract

The invention relates to a longitudinal traveling wave differential protection method suitable for a symmetrical bipolar DC line. The method comprises the following steps: carrying out rational function fitting on characteristic impedance and a propagation function of a transmission line; measuring the voltage and current at the two ends of the DC line in real time, and decoupling a positive electrode and a negative electrode which are coupled with each other through a Clenberg transform matrix, and obtaining the mutually independent 0-1 mode voltage and current, and calculating a forward traveling wave mode component and a reverse traveling wave mode component at the two ends of the line by the 0-1 mode voltage and current; calculating a 0-mode reverse traveling wave differential value Bdm0 and a 1-mode reverse traveling wave differential value Bdm1 at a protection installation position; starting the criterion action after the condition of Bdi1<-delta is detected in the three continuous sampling periods; taking the moment when the condition of Bdi1<-delta is detected for the first time as the integral starting time t0, wherein the integral duration is tDW; calculating the integralof Bdi1 as a 1-mode criterion; if the 1-mode criterion is smaller than -delta(1tDW), determining that a fault exists in the area; and then calculating an integral of Bdi0 as a 0-mode criterion, judging a fault type according to a calculation result, and selecting a fault electrode.

Description

technical field [0001] The invention belongs to the field of relay protection of electric power systems, and in particular relates to a longitudinal traveling wave differential protection method for direct current lines of ultra-high voltage and long-distance direct current transmission systems. Background technique [0002] The fast and reliable identification of DC line faults is a key problem to be solved urgently in the development of DC transmission system. The protection strategy of the existing DC transmission project is: the main protection is traveling wave protection and differential undervoltage protection, and the current differential protection is the backup protection. Traveling wave protection and differential undervoltage protection have fast action speed and are not affected by distributed capacitance of long lines, but are susceptible to noise interference, high-resistance ground fault sensitivity is insufficient, and reliability is not high; current differ...

AI Technical Summary

Problems solved by technology

Traveling wave protection and differential undervoltage protection have fast action speed and are not affected by distributed capacitance of long lines, but are susceptible to noise interference, high-resistance ground fault sensitivity is insufficient, and reliability is not high; current differential protection is effective for high-resistance In order to avoid the influence of transient current, the time delay is long, which does not meet the requirements of quick action of DC transmission line protection

[0003] In recent years, domestic and foreign scholars have conducted a lot of research on the shortcomings of DC line protection: introducing signal processing methods such as wavelet transform, empirical mode decomposition, and S transform into traveling wave protection to improve the reliability of protection. These methods only use The initial fault traveling wave information requires extremely high sampling frequency; the DC line fault is identified by using the special fault characteristics generated by the DC line smoothing reactor, but the distribution parameter characteristics of the line are not considered; The new type of longitudinal protection principle is constructed mainly through simulation observation, lack of theoretical analysis; the line distribution parameter model is used to improve the longitudinal current differential protection, but the action time limit still cannot meet the requirements of flexible DC transmission. System quick action requirements, can only be used as a backup protection

[0004] In addition, many scholars have ignored the frequency-varying characteristics of the distribution parameters of ultra-high voltage and long-distance transmission lines in the analysis process, and the transient process of the DC system contains rich frequency components.

These frequency components may have adverse effects on the existing protection principles, and at the same time provide more fault information. Therefore, it is of great significance to study the protection principles of DC transmission systems based on frequency-variable parameter line models for the development of DC power grids.

Images