Asymmetry relay

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The asymmetry relay is an electrical component for monitoring low-voltage networks with three-phase alternating current which can be galvanically separated from the rest of the network. Its task is to detect a possible system fault in good time before major damage occurs.

application

Asymmetry relays are used in three-phase AC voltage networks up to 690  V ~ . The relay has the task of monitoring voltage asymmetries and voltage drops in the network. It does not require a star point connection and is therefore universally suitable for three-wire networks (e.g. 3- wire 460 V) and four-wire networks (e.g. 3 / N AC 460/254 V). The response values ​​for asymmetry , undervoltage and time delay are infinitely adjustable. Auxiliary and signaling voltages are galvanicdisconnected from the grid. Special input transformers dampen the transmission of interference factors from the network to be monitored. For use in networks with a high proportion of voltage harmonics and voltage peaks , special protective circuits are built into the relay (e.g. for networks with connected inverters or frequency converters ). Potential-free contacts are available for the output signals. The main areas of application for the relay are systems with production processes that are susceptible to interference, such as chemical plants, EDP systems, the food industry as well as in explosion- and fire-endangered facilities.

Mode of action

The actual values ​​of the external conductor voltages are galvanically isolated from the network and recorded by special measuring transformers. These measured variables are filtered and fed to the evaluation circuit. The electronic evaluation unit compares the actual values ​​with each other and evaluates the difference to the asymmetry detection. At the same time, the actual values ​​are monitored for their absolute size by comparing them with a specified target value for the detection of undervoltage. Response values ​​for asymmetry and undervoltage can be set separately and depend on the respective system configuration. If one of these values ​​is undershot or exceeded by one or more actual values, the relay will respond after an adjustable delay time. The time delay remains fully effective even if one phase fails. In the event of a total power failure, the set delay time becomes ineffective. The relay is reset automatically and without delay when all actual values ​​have reached the specified setpoints. When setting the relay, the switching hysteresis (usually 2% of the response value) must be taken into account.

literature

  • H. Koettnitz, G. Winkler, K. Weßnigk: Fundamentals of electrical operating processes in electrical energy systems. VEB German publishing house for basic industry, Leipzig 1984, ISBN 3-342-00087-2 .