The protection of power transformers may be divided intotwo groups: against overloads and against short circuits (whichmay or not involve earth) The main protection of powertransformers is usually performed by differential relays (87)，gas relays installed in the main tank (63) and in the on load tapchanger tank (63C) and safety devices for pressure relief(63VS) On the other hand， usually non-directionalovercurrent relays (51) with inverse or very-inverse timecurves are applied to provide backup Theseovercurrent relays in most cases also have an instantaneousunit (50)Overcurrent and differential relays should be fed byindependent current The operation of any of thepreviously cited relays should trip the circuit breakersresponsible for disconnecting the power In orderto avoid unnecessary outages， these relays should not operateduring magnetizing transients or when overloads are Gas and differential relays are considered selective， so theiroperation usually implies the existence of internal faults in thetransformer and the necessity of Consequently，when they detect a fault they not only send trip signals tocircuit breakers in order to interrupt the fault， but also lockthem open through the lockout relay (86) Since nondirectionalovercurrent relays may operate when the fault isexternal， they only switch circuit breakers to the open positionthrough the operation of an auxiliary relay (94)This typical protection scheme is shown in figure Part ofthe previously cited protective devices are supplied with thetransformer (63， 63C， 63VS) and part are installed in panelslocated in the substation control room (87， 51， 86， 94) Moreinformation on these relays and on power transformerprotection systems may be found in [3] 翻译：电力变压器的保护可以分为两组:防止过载和防止短路（可能涉及地线 )。电力变压器的主要保护通常是由变压器差动继电器(87)，主槽上的气体继电器(63)和转换槽上的负荷开关(63C)和减压的安全设备(63VS)。另一方面，通常有反时特性曲线的非定向过流继电器常用来提供后备保护。这些过电流继电器在大多数情况下也有个瞬时单位(50)。 过载电流和差动继电器应该由独立电流互感器供电。任何对于前期引用继路器的操作应当由于失去和电力变压器的链接而触发断电器。为了避免不必要的中断，这些继电器不应在磁化瞬变或者过载可承受的时候进行操作。 气体和差动继电器是可选的，所以它们操作通常意味着在继电器中存在内部故障和变压器需要必要维护。因此，当他们探查到一个错误，它们为了防止故障发生不仅发出触发信号给断电器，同时也闭锁继电器。由于过流继电器在故障出现时可以自动修复，它们仅仅在使用辅助继电器的时候将断电器的开关切换到开的位置 这款典型的保护方案如图1所示。部分前期引用保护装置由变压器(63，63C，63VS)来支持，部分则安装在位于变电站控制房间的面板上(87，51 86，94)。更多。关于这些继电器和电力变压器保护系统的信息可在[3]中找到。
