Description
Over/undervoltage protection assemblies type RAEDK are available in a number of variants for measurement ofone-, two- or three-phase power system ac-voltages. The relays are suitable for protection and control applications. The relays provide two-stage over- and/or under-voltage protection in a very compact packaging allowingmany possible mechanical assemblies. I.e. 19” rack-mounting or various forms of panelmounting using theCOMBIFLEX mounting details. The RXEDK 2H voltage relay element used is characterised by a wide setting range, high setting resolution, lowburden on the input voltage transformer, built in timing ranges, selectable inverse or definite time, high resetratio, high continuous overload rating and built in LED indication of operation, starting and tripping of the twostages.
The possibility of specifying built-in frequency filters enhances the application range. E.g., there are versions tomeasure voltages of specific frequencies occurring in the power system, e.g. 150-180 Hz. A bandpass filter for50-60 Hz is also available. Products based on the RXEDK 2H measuring relays are available as assemblies of measurement relays. Versionshaving optional additional devices are also available. E.g. a test switch type RTXP 18 is available as an option, aDC-DC converter RXTUG 22H and a tripping relay RXME 18 are other standard options. A number of standardized protective packages are thus available. Standard schematics are provided for ease of protection selection andfor user maintenance and servicing guidance. Protection assemblies combining different COMBIFLEX modules may be specified and built in similar arrangements.
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.
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