Research On HVDC Line Protection Based On Characteristic Band Analysis

As an important part of the modern power system system and one of the key technologies for the construction of the global energy Internet.(U)HVDC transmission technology has a large power transmission capacity,a long transmission distance,flexible power adjustment,and strong economics during construction and operation.These advantages provide important support for solving global energy problems,improving the climate and environment,and promoting the development of clean energy.At the same time,it has become a powerful technical guarantee for national energy security,a major R & D area for grid technology innovation,and a hard core strength of strong smart grid construction.In recent years,China's(U)HVDC transmission project construction and technology research and development have ushered in a "golden period" of development.HVDC transmission profoundly affects the shape of the power grid.While significantly improving the optimization of the large-scale resource allocation of the power grid,it also poses new technical challenges to the safe and stable operation of the power grid.In the(U)HVDC transmission project,the probability of DC transmission line failure is significantly higher than other locations,so optimizing and improving the basic performance of DC transmission line protection is of great significance to ensure the safety and stable operation of DC transmission lines.Most of the DC transmission projects that have been put into operation currently use traveling wave protection as the main line protection.The protection is fast-moving,but its reliability and sensitivity are greatly affected by interference factors such as line length and transition resistance.Therefore,on the basis of meeting the fast-moving requirements,research and design of(U)HVDC line protection with higher reliability and sensitivity has important theoretical significance and practical value.The work and results obtained in this paper are as follows:This paper proposes a single-end protection main protection scheme suitable for UHVDC transmission lines.First,the amplitude-frequency characteristics of the line boundary elements composed of smooth-wave reactors and DC filters at both ends of the actual DC transmission line and the attenuation characteristics of long-distance long-distance line signals are analyzed,and the generalized S transform is used as an analysis tool for fault transients.Analyze the transient energy sum of the characteristic frequency band components and the average transient energy sum of the adjacent frequency bands,and use the square of the ratio of the energy sum of the two to form a criterion to realize the fault discrimination inside and outside the protected area.The high and low frequency band components are calculated.The ratio of partial S-transform energy sums distinguishes between line faults,lightning strike interference,and lightning strike faults;the fault pole selection is achieved by comparing the magnitudes of the harmonic voltage amplitudes in the characteristic frequency bands of the two poles.After the protection is activated,the main functional unit is the internal and external fault identification unit,lightning interference identification unit and fault pole identification unit.At the same time,a fault segment locating method for HVDC lines based on S-transformation relative entropy is proposed.This method can be used to distribute high-voltage DC transmission lines with multiple measuring points in a distributed manner.Based on the analysis of the relationship between the fault location and the polarity of the voltage and current changes at each measurement point,when the fault point is located between two adjacent measurement points,the energy relative entropy of the fault current component at the two measurement points Large,when the fault point is located on the side of two adjacent measuring points,the relative entropy of the fault current component of the two measuring points is small.Then the interval formed by a set of measurement points with the largest relative entropy of the S transform energy is the fault interval.Finally,the PSCAD simulation software is used as a test platform to perform a complete and systematic simulation test on the above-mentioned single-ended line main protection and fault section location method in the electrical model of the(U)HVDC transmission system established.Simulation results verify the theoretical rationality and practical feasibility of the proposed method.