Drives and Controls Magazine
Two-stage residual current relays will reduce shutdowns
Published:  11 June, 2013

Residual currents can occur in industrial plants as a result of various problems including: inadequate insulation of terminals or cables; humidity; contamination; or ageing materials. Simple monitoring relays are available that raise and alarm or trigger a shutdown when they detect a rise in residual currents.

Siemens has come up with a more sophisticated approach using a pair of relays that have two outputs that can be assigned to different levels of currents, allowing the first to provide an initial warning and the second to provide a tripping function. This will allow users to react early to the warning signal and avoid unplanned shutdowns.

The Sirius 3UG4625 and 4825 relays can monitor currents from 30mA to 40A and are designed to be used with a new range of differential current transformers in six sizes that can monitor phase currents up to 630A. The accuracy of the two components working together is said to be within 7.5%.

Siemens' residual current relays offer two levels of protection

The 4825 version has an IO-Link interface that can link it to higher-level controllers and allows it to be parameterised remotely. The link can also be used to transfer measured data and diagnostics to other systems.