直流线路行波传播特性的解析

Study on the Propagation Characteristics of Traveling Waves in HVDC Transmission Lines on the Basis of Analytical Method

高压直流(high voltage direct current,HVDC)输电线路行波保护及测距装置的分析、整定主要依赖于数值仿真方法,难以反映行波过程的物理本质和影响因素,也无法进行整定计算。分析了直流线路行波在故障点及包含直流滤波器的线路末端的折反射规律,在此基础上推导了基于无畸变传输线模型的行波解析解,用以研究直流滤波器、故障电阻和故障位置对直流线路行波的影响。研究表明:直流滤波器使行波波头由阶跃波变成衰减的振荡波,从而使其变化率和幅值都减小;过渡电阻主要影响行波波头的幅值大小。基于该解析表达式计算而得的行波变化率可用于实际工程中的行波保护整定。在EMTDC仿真软件中,结合中国某实际直流系统建立仿真模型,大量的仿真结果验证了所得出的解析解以及分析结果的正确性和有效性。

The protection and fault locator schemes based on the traveling wave are evaluated by the numerical integral method for high voltage direct current （HVDC） transmission lines. But the essential principles, influence factors of the traveling wave or the setting values of the protection cannot be studied effectively. Analytical treatment was employed to indicate the reflection principles of the traveling wave at the fault position and at the terminals with filters at the DC side, based on which the analytical solution of the traveling wave in the distortionless HVDC transmission line was derived. With the analytical expression, the effects of the filter, the fault resistance and the fault position on the traveling wave were evaluated. It is shown that the initial incident wave with the step waveform is changed into the attenuated sinusoidal wave because of the DC filter. As a result, both the amplitude and the derivative of the wavefront decrease. The initial amplitude mainly depends on the fault resistance. Furthermore, the change rate of the voltage which is the dominating discriminant of the existing traveling wave protection can be obtained for the setting calculation. The EMTDC simulation model of a real I-WDC transmission system in China was constructed and lots of simulation results show the effectiveness and credibility of the proposed analytical expression and conclusions.