User manual 09/2009 - Schneider Electric

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User manual 09/2009 - Schneider Electric

The Protection FunctionElectrical Distribution ProtectionPresentationMicrologic 5 and 6 trip units on Compact NSX circuit breakers provide protection against overcurrentsand ground fault currents for all types of commercial or industrial application.Micrologic 5 and 6 trip units offer protection characteristics that comply with the requirements of standardIEC 60947-2 (see the Compact NSX circuit breakers - User manual).DescriptionThe installation rules closely define the protection characteristics to be used taking account of:• Overcurrents (overloads and short-circuits) and potential ground fault currents• Conductors to be protected• The presence of harmonic currents• Coordination between the devicesMicrologic 5 and 6 trip units are designed to satisfy all these requirements.Discrimination Between DevicesCoordination between the upstream and downstream devices, especially discrimination, is essential tooptimize continuity of service. The large number of options for setting the protection parameters onMicrologic 5 and 6 trip units improves the natural coordination between Compact NSX circuit breakers(see the Compact NSX 100-630 A - Catalogue).3 discrimination techniques can be used:1. Current discrimination, which corresponds to staging of the long time protection pick-up2. Time discrimination, which corresponds to staging of the short time protection pick-up3. Energy discrimination, which corresponds to staging of the circuit breaker energy levels: this appliesfor very high intensity short-circuit currents.Discrimination RulesThe discrimination rules depend on:• The type of trip unit on the circuit breakers installed upstream and downstream: electronic or thermalmagnetic• The accuracy of the settingsLV434104 09/2009 37

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