电气类外文翻译--基于继电保护的电力系统监控设备-电气类(编辑修改稿)

电气类外文翻译--基于继电保护的电力系统监控设备-电气类(编辑修改稿)内容摘要：

of overall data transmission rates which are proportionally lower. For monitoring and control applications the slower data rates remain acceptable and serial type munications are used almost exclusively. The munications hardware most monly used by protective relays at present conforms to the EIA’s RS232 standard. This takes the form of the familiar 25 or 9 way 39。 D39。 connector. This has usually been used to connect the relay to a personal puter (sometimes indirectly, via a modem) allowing the relay to be setup and allowing post fault information to be extracted. RS232 connections are convenient because of their almost universal availability. RS232 connections do have a number of limitations which make them less suitable in monitoring and control applications. The most serious of these is that RS232 is designed for point to point systems. A single device can only municate with one other device over a given munications with more devices are required, as they are for data monitoring and control within substations, separate links must be provided. Alternatively, multiplexers or code switches could be added though this would generally impose some sort of limitation on how the links are operated. RS232 also imposes a limit on the physical length of the munications link of just over 15, and a maximum data rate of . This can also be overe but again requires additional equipment. Finally RS232 does not offer any significant level of isolation. Optically isolated RS232 ports can be created but these are expensive. A more suitable munications standard is RS485. This allows for a multidrop system with up to 32 nodes on a single spur, sufficient to connect at least a single bay of relays. RS485 specifies a maximum transmission distance of 1200 metres and a maximum data rate over this distance of l00kbaud, significantly further and faster than RS232. It uses a balanced driver and differential signaling which is less susceptible to interference than the unbalanced driver referenced to ground as used in RS232 systems. RS485 requires a single shielded twisted pair cable which is low cost and easy to terminate. Within the electrical industry in general this has typically been terminated in either 25 or 9 way 39。 D39。 connectors similar to those used by RS232. In a substation 外文翻译（ 原 文） environment these connectors are not really suitable and a pair of conventional terminals is preferred. The use of optical fibres to connect directly between relays remains expensive for most users, especially at distribution voltage levels. Fibres are however suitable for connecting the local work of relays to remote master stations where distances exceed 1200 metres or where the risk of interference is high. In such cases modems are used to interface a group of relays to an optical fibre. As with electrical based munications, a number of different solutions are available. For distances of up to four or five kilometers, 850nm multimode fibres are quite adequate and offer relatively low plexity. For greater distances up to around 25 kilometres, 1300nm single mode fibres can be used. These require more plex transmitters and receivers, however their widespread use in the telemunications industry means that they may well bee more economic than 850nm fibres even over short distances. Serial data munications may be classified as either asynchronous or synchronous. RS232 munications ports on protectivc relays are invariably asynchronous. In asynchronous systems timing or synchronization information is transmitted together with each character. In synchronous systems either a separate clock is transmitted or the receiver derives the clock information from the data itself. Synchronous systems are more plex than asynchronous systems but roughly 20% more efficient. More importantly intercharacter gaps on synchronous systems are fixed. This allows frequency modulated (FM) coding methods to be used which result in no DC ponent in the signal. Hence the problems of isolation in RS232 systems can easily be overe using simple transformer isolation. A second benefit of FM coding is that the two signal wires are nonpolarized and may be freely interchanged throughout a system. Modern serial control chips allow the extra plexity of synchronous transmission to be absorbed at no extra cost. In summary, of the mon munications interfaces, multidrop synchronous RS485 transmission using some form of FM encoding is currently the most suitable for use in power system data measurement and control applications. This can provide fast economic munications with electrical interference immunity sufficient for power system environments. Communications Language Successful digital munications depends not just on patible munications hardware but also on the munications language and protocol that are used. Traditionally relay manufacturers (in mon with those in other fields) have 外文翻译（ 原 文） developed their own languages. This has been less important in the past when there has been no need to integrate the relays into control systems. When the relays have been integrated a bespoke solution has been necessary with custom programming for each different relay. The costs of this have been uneconomic for most users. Until now no language suitable for use by all protective relays has been proposed. The major drawback with most languages is that they assume the master station must have an intimate knowledge of the relay. If a particular piece of data has been required it has been asked for using its memory location in the relay or some device specific code. This address must be explicitly coded into the master station software. Moreover the relay has typically responded with raw unformatted data. The master station must assume a scale for the reply and convert it accordingly. Where a large amo。