高压输电线路是重要的电力系统设备，保证输电线路在正常运行和故障情况下的安全是电力系统安全可靠运行的重要内容。现有的输电线路继电保护根据所使用的电气量不同有不同的保护原理、构成方式和优缺点，比如反映工频电气量的继电保护可靠性高，但是动作时间稍慢，而且受互感器饱和、长线分布电容以及过渡电阻的影响较大；反映暂态行波故障信息的行波保护具有超高速动作性能，但保护只能在故障初瞬动作，而且可靠性较低。研究一种在故障初瞬、故障暂态以及故障稳态过程中都能可靠动作的、普遍适应各种故障情况的新型输电线路继电保护就显得尤为重要。方向比较式纵联保护是高压输电线路的主要继电保护方式，把它作为重点研究对象和突破口无疑更具有现实意义。 围绕输电线路方向比较式纵联保护研究，本文主要做了以下工作： 1）提出了统一行波的概念和支撑该概念的故障分析方法，为后续研究奠定了基础。 2）将瞬时无功（广义无功）理论引入输电线路方向比较式纵联保护的研究，并提出了无功能量（虚能量）和复能量的概念。 3）在统一行波和瞬时无功理论的基础上，提出了用于方向比较式纵联保护的核心元件－方向元件，它可以利用故障暂态信息和稳态工频信息判断故障方向，它较好地兼顾了保护的速动性和可靠性，在整个故障过程中都能够可靠动作。 4）针对大电源侧方向元件灵敏度不足的问题，提出了基于统一行波的电压补偿原理和算法，具有高速和广泛适用的优点。 5）提出了基于统一行波的线电压补偿式故障选相元件，具有高速、灵敏和广泛适用的优点。 6）选用了合适的故障分量提取算法、频率跟踪算法、起动元件、通信模式等保护元件，并给出了基于统一行波的方向比较式纵联保护的软硬件构成方案。
High-voltage transmission lines are important equipments in power system, so it is the main content of security and reliability of the power system to ensure the safety of transmission lines both in normal operation state and fault condition. The existing protection relays for transmission lines can be classified into several categories by the electrical quantities used by the protections. Each category has its own principle, structure, advantage and disadvantage. Conventional protection relays based on power frequency component possess the advantages of stability and reliability, but their operation speed is comparatively slower, and their performance is influenced greatly by saturation of current transformer, distributed capacitance, fault generated resistance and so on. Protection relays based on traveling wave have the highest speed theoretically, but they can only operate in instant beginning of the fault course and their reliability is comparatively slower. Hence, it is important to research a novel protection for transmission line that can operate reliably and stably in instant beginning of the fault course, fault transient state and fault steady state. Carrier-pilot protection with directional comparison is the main protection of high-voltage transmission lines, so it has practical significance to regard carrier-pilot protection with directional comparison as the main research object and breakthrough in this dissertation. Material works and innovations of the dissertation are as follows: 1) Present the concept of uniform traveling wave and fault analysis methods which can support the concept. It lays a theory foundation for future research. 2) Instantaneous reactive power (generalized reactive power) theory is introduced into the research of directional protection, and two new concepts of reactive energy (virtual energy) and complex energy are presented. 3) Based on the theories of uniform traveling wave and instantaneous reactive power, a new directional component which is the foremost part of carrier-pilot protection with directional comparison is put forward. Both transient and steady state fault information can be used by this component to judge the fault direction. It gives attention to both the speed and reliability of the directional protection and could operate reliably in the whole process of the fault. 4) A new high-speed voltage compensation algorithm is presented to settle the problem of low sensitivity at strong side of the system. 5) A new fault phase selector by fault component of compensation voltage based on uniform traveling wave is presented. It has the advantages of high speed and high sensitivity and could be used widely. 6) Proper algorithm to extract fault component, tracking algorithm for power system frequency, starting algorithm and communication mode are selected to meet the need of this directional protection. And the design project of hardware and software is presented at last.
