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1、继电器继电器是电力系统保护的关键的组成部分，继电器是一种装置，它依据系统信息，履行一个或多哥开关作用。这里所说的“信息”包括电信号和电流，一般来自互感器的输出，继电器“决定”开（或关）一组或多组正常情况下关（或开）的触点，它的这种作用一般是为断路器的跳闸线圈励磁，用断路器开断电路，从效果上继电器的作用是将命令传达至跳闸结构而得名。电力系统保护的原理与所使用的继电器类型无关。例如，如果一个电路或电机的电流超出了其负荷能力，则有必要采取补救措施无论其具体工作机理如何，识别这种情况并采取补救措施的装置被定义为过电流继电器。由于机电型继电器的功能容易描述，这里借用对机电装置性能的说明代表对继电器和继电
2、系统进行总体描述。继电器具有以下性能：可靠性：这里指如果继电器已闲置了一段时间，甚至是若干年，在需要时应能迅速起作用。其可能发生的动作紊乱会造成数百万美元的损失。选择性：继电器对诸如系统瞬间切换或负载突变之类的无害的异常情况不作反应。快速性：继电器应尽可能快地（瞬间）做出决断与动作，在需要延时，延迟动作时间应能预测并能准确设置。灵敏性：如果按设计需要动作时，则即使在临界条件下，也不得发生拒绝动作的现象。瞬动性：是指在不需要延时时，应能立即动作。Relays待添加的隐藏文字内容3A key component in any power system protection scheme is th
3、e relay.A relay is a device that，based on information receved from the power system，performs one or more switching actions.The “information” referred to consists of signals and currents，typically the output of instrument transformers.The relay “decides” to close (or open ) one or more sets of normal
4、ly open (or closed ) contacts.The switching action typically energizes the trip coil of a circuit breaker，which then opens the power circuit.It，in effect，“relays” the decision to trip to circuit breaker，which actually performs the act thus its name.The principle of protection of electric power circu
5、its are quite independent of the relay desgns which maybe applied.For example，if the current to an electric circuit or a machine is greater than that which can be colerated，it is necessary to take remedial action.The device for recognizing the condition and initiating corrective measures would be te
6、rmed as anover-current relay regardless or the mechanisms by which the function would be accomplished.Because the functions of electromechanical devices are easily described，their performance wills ever as a basis for presenting a description of relays and relay systems in general.Relays must have t
7、he following characteristics：Reliability：The nature of the problem is that the relay may be idle for periods extending into years and then be required to operate with fast responds，as ntended，the first time.The penalty for failure to operate properly may run into millions of dollars.Selectivity：The
8、relay must not respond to abnormal，but harmless，system conditions such as switching transients or sudden changes in load.Speed：The relay should make the decision to act as close to instantaneously as possible.If intentional time delay is available，it should be predictable and precisely adjustable.Sensitibity：The relay must not fail to operate，even in borderline situations，when operation was planned.Instantaneous：The term means no intentional time delay.
