专业外语课外作业
西南交通大学峨眉校区
2012 年10 月30 日
Line impedance functions in the terminal.
General
The distance protection function is the most widely spread protection function in tr ansmission and subtransmission networks. It is also becoming increasingly importa nt indistribution networks. The main reasons for this are:
Its independence on communication links between the line ends, because for its operation,it uses information about the locally available currents and voltages.
The distance protection forms a relatively selective protection system (non-unit pro tectionsystem) in the power network. This means that it can also operate as a re
moteback-up protection for other primary elements in the network.
The basic requirements for modern line protection, such as speed, sensitivity and selectivity, with their strict requirements for dependability and security (availability), aregetting more stringent. In addition, modern distance protections must be able to operate in networks with existing distance relays, which are mostly designed in a different technology (static or even electromechanical relays).
Older distance relays protect in many cases power lines only at phase-to-phase a nd three-phase faults. Some other protection is used for phase-to-earth faults.
The flexibility of modern distance protection is for this reason very important. This especially applies when it is used in a complex network configuration, for example, on parallel operating multicircuit lines and on multiterminal lines.
The selective operation of the distance protection does not depend on communicat ion facilities between two line ends. At the same time, the distance protection can detect faults beyond the current transformers at the remote terminal. This function ality makes it an ideal complement to the line differential protection function that c annot detect faults beyond the current transformer at the opposite terminal. Distance protection zones
The distance protection function in REx 5xx line protection, control, and monitoring terminals consists of three to five independent distance protection zones, each of them comprising three measuring elements for phase-to-earth (Ph-E) faults and/or three measuring elements for phase-to-phase (Ph-PH) faults. Different terminals s uit different requirements in different networks on various voltage levels. For this re ason, some characteristic parameters of the distance protection function differ from terminal to terminal. For detailed information, please refer to ordering particulars f or each line protection terminal REx 5xx separately.
Distance protection zone five differs from other zones with respect to its speed of operation. It starts faster than other distance protection zones and might have for t his reason higher overreaching for different system transients. It is for this reason suggested to use it only for the applications, which permit higher overreaching, (i.
e. switch-onto-fault function) or as a time delayed distance protection zone with ti me delay longer than 100 ms.
Complement to the line differential protection
The distance protection function can become optional protection in some line differ ential protection terminals (REL 561, for example). At the same time it represents the primary protection for faults beyond the current transformers at the opposite te rminal. This functionality is achieved by the time delayed overreaching zone (gener ally zone 2), which covers at least the adjacent busbar and thus forms a
primary or back-up protection for the busbar. So the overreaching zone should be continuously in operation.
An underreaching zone (generally zone 1) can form a back-up to the line different
ial protection. There is no need for this function as long as the differential protecti on is in operation. To minimize the risk of unwanted operation from zone 1, this f unction can be activated only when the differential function is out of operation. Th e most likely cause to lose the differential protection is a failure within the commu nication system.
The communication scheme used with the distance protection should for this reas on use another communication channel than the one used by the line differential protection.
Set of simplified setting parameters
Each distance protection zone comprises basically completely independent setting parameters for phase-to-earth, and for phase-to-phase measurement. This is an a pplication advantage in complex network configurations and in networks, where it i s required to adjust the newly applied distance protection functions to the existing other types of relays (overcurrent earth fault, for example).
A set of simplified optional parameters is available optionally for applications, where equal zone reaches for all kinds of faults are a standard practice. See the table of setting parameters and the setting instructions.
Line impedance
Basic characteristics
The distance protection function, as built into the REx 5xx line protection terminal s, is a full-scheme distance protection. This means that it has individual measurin g elements for different types of faults within different zones.
Depending on the type of terminal, it consists of up to five independent, impedan ce-measuring zones, each has a quadrilateral characteristic. RL and XL represent line resistance and reactance and RF represents the resistive reach of a protectiv e zone.
终端的线路阻抗功能
概述
距离保护装置是在输电网和变电网中应用得最广泛的一种保护装置。在配电网中它也变得越来越重要。主要原因如下：
*它在线路两端之间的通信通道中的独立性，是因为它是利用本地有效电流和电压信息动作的。
*距离保护在电力网中形成了一个相互关联的有选择性的保护系统（非单元式的保护系统）。
这意味着它也可以作为网络中其他主要元件的远后备保护。
现代线路保护的基本要求，比如快速性，灵敏性和选择性，以及在可靠性和安全性方面的严格要求，变得越来越严格。另外，现代距离保护在网络中必须能够与阻抗继电器配合动作，这是一种由不同技术设计而成的继电器（静态或者是机电式继电器）。
较早的阻抗继电器在多数情况下只用于电力线路的相间和三相故障的保护，一些其他保护用于接地故障中。
由于这些原因现代距离保护的灵活性非常重要，当它用于一个复杂的网络结构时尤其合适。比如并列运行的多回线路和辐射网。
距离保护的有选择性动作不是依靠线路两端间的通信设备。距离保护能在远方末端电流互感器处检测到故障。这个功能使它成为那些不能检测到超过反方向末端电流互感器范围以外故障的线路差动保护的一个理想补偿。
距离保护范围
在线路REX 5XX的保护、控制和终端监测方面的距离保护装置由3到5个独立的距离保护范围组成，每一个包括了3个接地故障的测量元件和3个相间故障的测量元件。对于各种不同电压等级在不同的电网中，不同的终端要适合不同的要求。由于这个原因，距离保护装置的一些特征参数各终端之间是不同的（要了解详细内容，请查阅线路保护终端的分类细节）。距离保护区域5不同于其他段在于它动作的快速性。它比其他距离保护段启动快，而且在不同的系统暂态过程中，由于这个原因误动的可能性就更高了，因此它只适用于以下情况：允许更高越限或者作为具有超过100ms延时的延时距离保护段。
线路差动保护的补充
在一些线路差动保护终端设备中（如REL 561）距离保护装置能够成为一个有选择性的保护。同时它是超出反方向末端电流互感器以外故障时的主保护，这个功能由带延时段实现（如II段），它覆盖了所有相邻母线，因此形成了母线的主保护或后备保护。所以超越段应处于持续动作状态。
保护范围为部分线路的保护段（如I段）可以作为线路差动保护的后备。只要差动保护动作这个功能就不需要了。为了减小I段误动的风险，可以在差动保护拒动时将其投入，差动保护失灵的最大原因就是通信系统故障。
由于这个原因用于距离保护的通信方案应该使用另一个通信途径而舍弃用于线路差动保护的那一个方案。
简单参数的整定
每一距离保护段基本上包含了作为相对地、相间测量的完全独立的整定参数。这是复杂网络结构中和那些被要求使新配置的距离保护装置适应目前其他类型继电器的网络的一个优势情况。
一套简明的可选择参数适用于反映各种类型故障的相同最大保护范围是一个标准惯例的场合。参看整定参数和整定操作说明表格。
基本特性
作为合成到线路REX 5XX保护终端的距离保护装置是一个全方案的距离保护。这意味着在不同范围内对于各种类型故障它都有单独的测量元件。
根据终端类型，它至少由5个独立的阻抗测量范围组成，每一个都是四边形特性。RL和XL 代表线路电阻和电抗，RF代表保护范围的电阻最大值。
生词表
indistribution 配电
subtransmission 变电
relay 继电器
Current transformer 电流互感器
Ideal compensation 理想补偿
Radiation network 辐射网
Characteristic parameters 特征参数
differential protection 差动保护
Impedance 阻抗
Static characteristics 静态特性
难句分析
1 Its independence on communication links between the line ends, because for its operation,it uses information about the locally available currents and voltages
它在线路两端之间的通信通道中的独立性，是因为它是利用本地有效电流和电压信息动作的。
本句中available currents 是指有效电流。
2 Modern distance protections must be able to operate in networks with existing distance relays, which are mostly designed in a different technology.
现代距离保护在网络中必须能够与阻抗继电器配合动作，这是一种由不同技术设计而成的继电器.
本句中existing distance relays要翻译为阻抗继电器
3 A set of simplified optional parameters is available optionally for applications, where equal zone reaches for all kinds of faults are a standard practice.
一套简明的可选择参数适用于反映各种类型故障的相同最大保护范围是一个标准惯例的场合。
本句中optional parameters是选择参数的意思，where引导一个状语从句。