【正文】 ible advantage that is not easily realizable in a conventional system. This is the ability to change the relay characteristics (settings) as the system conditions warrant it. With reasonable prospects of having affordable puterbased relaying which can be dedicated to single protection function, attention soon turned to the opportunities offered by puterbased relaying to integrate them into a substation, perhaps even a systemwide network. Integrated puter systems for substations which handle relaying, monitoring, and control tasks offer novel opportunities for improving overall system performance. Computer relayingThe electric power industry has been one of the earliest users of the digital puter as a fundamental aid in the various design and analysis aspects of its activity. Computerbased systems have evolved to perform such plex tasks as generation control, economic dispatch (treated in chapter 11)and loadflow analysis for planning and operation , to name just a few application areas. research efforts directed at the prospect using digital puters to perform the tasks involved in power system protection date back to the miensixties and were motivated by the emergence of processcontrol puters a great deal of research is going on in this field, which is now referred to as puter relaying. Up to the early 1980s there had been no mercially availability protection systems offering digital puterbased relays. However, the availability of microprocessor technology has provided an impetus to puter relaying.*Microprocessors used as a replace*and solid state relays non provide a number of advantages while meeting the basic protection philosophy requirement of decentralization.There are many perceived benefits of a digital relaying system:1. Economics: with the steady decrease in cost of digital hardware, coupled with the increase in cost of conventional relaying. It seems reasonable to assume that puter relaying is an attractive alternative. Software development cost can be expected to be evened out by utilizing economies of scale in producing microprocessors dedicated to basic relaying tasks. 2. Reliability: a digital system is continuously active providing a high level of a selfdiagnosis to detect accidental failures within the digital relaying system.3. Flexibility: revisions or modifications made necessary by changing operational conditions can be acmodated by utilizing the programmability features of a digital system. This would lead to reduced inventories of parts for repair and maintenance purposes4. System interaction: the availability of digital hardware that monitors continuously the system performance at remote substations can enhance the level of information available to the control center. Post fault analysis of transient data can be performed on the basis of system variables monitored by the digital relay and recorded by the peripherals. The main elements of a digital puterbased relay are indicated in Figure 959. The input signals to the relay are analog (continuous) and digital power system variables. The digital inputs are of the order of five to ten and include status changes (onoff) of contacts and changes in voltage levels in a circuit. The analog signals are the 60Hz currents and voltages. The number of analog signals needed depends on the relay function but is in the range of 3 to 30 in all cases. The analog signals are scaled down (attenuated) to acceptable puter input levels (10 volts maximum) and then converted to digital (discrete) form through analog/digital converters (ADC). These functions are performed in the block labeled “Analog Input Subsystem.”The digital output of the relay is available through the puter’s parallel output port, fivetoten digital outputs are sufficient for most applications.The analog signals are sampled at a rate between 210 Hz to about 2000 Hz. The sampled signals are entered into the scratch pad (RAM) and are stored in a secondary data file for historical recording. A digital filter removes noise effects from the sampled signals. The relay logic program determines the functional operation of the relay and uses the filtered sampled signals to arrive at a trip or no trip decision which is then municated to the system.The heart of the relay logic program is a relaying algorithm that is designed to perform the intended relay function such as over currents detection, differential protection, or distance protection, etc. It is not our intention in this introductory text to purse this involved in a relaying algorithm, we discuss next one idea for peak current detection that is the function of a digital over current relay. 譯 文繼 電 保 護微機保護電力系統(tǒng)保護領(lǐng)域中一個新發(fā)展是計算機 (通常為微型機) 來進行繼電保護. 雖然計算機能提供與傳統(tǒng)繼電保護相同的保護, 但它有一些優(yōu)點. 計算機繼電保護比機電式繼電保護裝置在邏輯能力和應(yīng)用的擴展方面要強的多. 計算機繼電保護可每秒進行多次電流,電壓以及其它量的采樣,通過A/D轉(zhuǎn)換器將這些模擬量轉(zhuǎn)變成數(shù)字量, 然后送入計算機. 在系統(tǒng)出現(xiàn)故障時,計算機可計算出故障電流的值和特性, 整定值的改變僅改變編程就可以了. 微機繼電保護還能進行故障的定位,這已成為其應(yīng)用時最受歡迎的特點之一. 此外,可配置自檢功能, 事件順序信息可下載到遠方計算機以進行繼電保護工作的快速分析.計算機繼電保護系統(tǒng)由一些功能明確的子系統(tǒng)組成. 雖然各具體子系統(tǒng)可能在某些細節(jié)方面有所不同, . 處理器是整個組合的中心. 它負責(zé)繼電保護程序的執(zhí)行,各定時功能的保持, . 隨機存取存儲器 (RAM) 存放著送入進行處理的輸入采樣數(shù)據(jù). 只讀存儲器 (ROM) 或可編程只讀存儲器 (PROM) 用來存放永久性程序. 在某些情況下, 若讀出時間足夠短,則程序可直接從ROM 執(zhí)行. 若不是這樣,在初始化階段,程序須從ROM 復(fù)制到RAM 中, 然后從 RAM 實時執(zhí)行. 可擦寫 PROM (EPROM) 用來存放某些參數(shù)(如繼電保護整定值), 這些參數(shù)可能經(jīng)常變動,但一旦設(shè)置好,即使計算機電源斷電,也保持不變.繼電保護的輸入是電壓和電流,或減少的是指示觸頭狀態(tài)的數(shù)字信號. 模擬信號須轉(zhuǎn)換成適合于變換到數(shù)字形式的電壓信號. 從電流互感器和電壓互感器的電流信號和電壓信號須限制到177。10V . 由于電流互感器二次側(cè)電流可高達數(shù)百千安,要產(chǎn)生提供給模 ─ 數(shù)轉(zhuǎn)換器 (ADC) 的需要的電壓就需要書mΩ 的并聯(lián)電阻. 另一種方法是采用中間電流互感器降低電流到較低的數(shù)值. 中間電流互感器還起到另一作用: 對電流互感器二次側(cè)與計算機輸入系統(tǒng)進行電氣隔離.只要提供各種功能所需要的輸入和輸出信號,數(shù)字計算機就可編程來執(zhí)行這些功能. 只要繼電保護的計算機執(zhí)行變電站的其它任務(wù)是很容易的事, 例如, 監(jiān)測變壓器和輸電線路中的潮流,控制斷路器和開關(guān)的分閘和合閘,對故障設(shè)備提供備用,都是繼電保護計算機可執(zhí)行的功能. 由于可編程能力和通信能力,計算機繼電保護具有傳統(tǒng)繼電保護系統(tǒng)中不可能實現(xiàn)的優(yōu)點. 這就是按系統(tǒng)條件準(zhǔn)許而改變繼電器特性 (整定值) ,注意力很快就轉(zhuǎn)到將計算機繼電保護綜合到變電站范圍,甚至系統(tǒng)范圍的機會. 變電站的綜合計算機系統(tǒng)可進行繼電保護,監(jiān)測和控制,這對整個系統(tǒng)的性能提供了新的機遇.微機繼電器電力工業(yè)已經(jīng)是數(shù)傳計算機的最早使用者之一如各種不同的設(shè)計和它的活度分析方面的一個基本的幫助。 計算機系統(tǒng)已經(jīng)進展運行如此復(fù)雜的工作如各種計劃交集運算的控制，經(jīng)濟的分配和負載 流程分析，只是命名一些區(qū)域。在屏幕上指示使用要運行在以電力系統(tǒng)保護期限內(nèi)是積極參與的工作數(shù)傳計