Description
Voltage relays are used in power systems for many different applications.The RXEDK 2H single-phase relay is provided with several new designfeatures, optional filters and wide setting-flexibilities that makes it suitable in practically all possible applications for over- and under-voltagerelays. The relay has two setting levels (steps), selectable for over or undervoltage. Thus one step can be for overvoltage and the other for undervoltage. Both steps may be set for instantaneous or definite time-delayedoperation. One step (U1) can be set for inverse time-delay as an alternative to the definite time delay function available for both steps. Standardrelays for 50-60 Hz, 16 2/3, 50-60 sharp and 150-180 Hz versions areavailable, using a built in filter. The standard 50-60 Hz relay has a flat frequency response characteristic to cover a wide frequency range. The RAEDK assemblies of single-phase relay elements are available in amultitude of standard packages, with or without test-switch and with orwithout DC/DC power supply. Single-, two- or three-phase RAEDK packages are available. Depending on the application requirements, a suitablestandard package may thus be selected. Special schemes may also be builtup, based on combinations of COMBIFLEX plug-in modules. Typical applications include single or multiple RXEDK 2H phase elements measuring two-stage overvoltage or combined over and undervoltage protection for system voltage supervision and various single relayelement neutral point or broken delta overvoltage applications for earthfault detection. The relays may be used for directly grounded systems aswell as high impedance or unearthed power systems.
Overvoltage relay protection at power system frequencies supplementssurge protection for transient overvoltages due to switching or atmospheric disturbances. Overvoltage stresses insulation on powerlines,cables and electrical apparatus, electrical machines etc. For transformers and transmission lines, overvoltage protection may beused to detect excessive voltages. A single overvoltage setting level is frequently used, either as an instantaneous or time-delayed protection function. Two overvoltage set levels are often used as well. One high set levelmay be instantaneous and the other lower set may be time-delayed,depending on the requirements for the specific application. A feature ofthe RXEDK 2H relay is its low transient overreach, which is of importance when using the instantaneous function. For transformers an instantaneous voltage “flash-over” protection on thelow voltage winding will detect high overvoltages occurring for faultsbetween the high voltage and the low voltage winding. This may be usedwhen the low voltage winding is not solidly earthed. An overvoltage relaymay be used for over-excitation protection in cases where the system frequency is not varying, otherwise V/Hz relays, e.g type RALK are recommended. A feature of the RXEDK 2H is the possibility of using the inverse timevoltage function (for U1, i.e. step 1) in which a faster operating time isobtained depending on the magnitude of the voltage-excursion. Thus asingle inverse over-voltage function may provide an alterative to a traditional two-step combination of an instantaneous and definite time-delayedovervoltage protection. Alternatively, the inverse function of U1 may beused for undervoltage and the U2 for instantaneous or definite timedelayed overvoltage protection. Since the RXEDK 2H is provided with two independently settable steps(U1 and U2) that may be used independently for overvoltage or undervoltage protection, good application flexibility is obtained over a widerange of voltages. The scale ranges of 5-480, 1-120 or 0.1-12 V are available in three versions.
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