ABB REM 610 Technical Reference Manual

Also see for REM 610: Operator's manual Product guide Installation manual Product guide Technical reference manual

Contents

ABB REM 610 Technical Reference Manual Manual pdf 138 page image

The pickup value of the ground-fault element is typically selected to be 5...30% Inof the fully developed ground-fault current and the operate time to be 0.5...2seconds.If a residual connection is preferred, the pickup value and operate time must be setslightly higher in order to avoid possible stability problems due to unbalance in themain transformers, as the unbalance will cause virtual ground-fault currents duringhigh phase current conditions. Also, an external stabilizing resistor can be used tocompensate too weak main transformers, thus preventing them from causingground-fault currents.6.1.7.1. Stabilizing virtual ground-fault currentsAn apparent ground-fault current caused by the difference between the phase currenttransformers connected in parallel may cause nuisance trippings of the ground-faultelement, especially during an overload. This can be avoided by using a stabilizingresistor in the ground-fault current circuit. The continuous power withstand of theresistor can be 30 W, for instance. The resistance value can be, for instance, 100 Ωwhen the 1 A input is used and 10 Ω when the 5 A input is used. The value of theknee-point voltage must be checked and should be >2 x U stab . The stabilizingresistor will also slightly reduce the ground-fault sensitivity.6.1.7.2. Increasing the sensitivity of the ground-fault protectionThe sensitivity of the ground-fault protection can be increased by using a relayprovided with a 1 A input instead of one with a 5 A input. This is possible in asolidly grounded network as well, because the thermal withstand capability of thecurrent input is normally high enough.6.1.8. Circuit-breaker failure protectionThe operate time of the CBFAIL should be set to be longer than the circuit-breakeropening time + the resetting time of the protection element with the longest resettingtime, with the exception of the thermal, temperature and phase reversal protectionelements and the external trip.6.1.9. Temperature protection (optional)Tripping due to a beginning thermal overload can be avoided by reducing the loadof the motor at an alarm of element 49/38-1/49/38-2.6.2. Protecting a circuit-breaker controlled motorData of the squirrel cage motor stated by the manufacturer:138REM 610REM 610 Motor Protection RelayTechnical Reference Manual - ANSI Version1MRS755537