Discrimination between residual-Current Devices

2-Implementing discrimination

Discrimination between upstream and downstream residual-current devices is necessarily of the current and time type.

It is ensured by correctly adjusting:

  • the operating-current settings

  • the non-operating and overall breaking times.

The following general discrimination rules ensure correct operation:

  • • in terms of the current, the setting for the upstream device must be double that of the downstream device (in accordance with the standardised rules for the operating / non-operating currents)

  • • in terms of the time, the non-operating time (time delay) for the upstream device must be greater than the total time (the intentional residual-current device delay and the breaking time of the breaking device) for the downstream device These two conditions are summed up here:

Definition

  • Uupstream I∆n ≤ 2 x downstream I∆n

Definition

  • Upstream non-operating time ∆T ≥ downstream total time ∆T

Note

  • It is possible to divide the installation into a number of groups of circuits and to protect each group using the suitable residual-current device.

  • The many fault, alarm and pre-alarm settings and time delays available in the Vigirex range makes it easy to integrate the residual-current relays at all levels in the electrical installation.

  • Coordination between the upstream and downstream devices in an installation makes it possible to cut the supply (by the protection relay) exclusively in the part of the installation where the fault occurred.

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