- Functional description

The overcurrent protection is used as backup protection for the short circuit protection of the protected object.It also provides backup protection for downstream network faults which are not promptly disconnected and thus may endanger the protected object.

Each phase-to-phase current is compared individually with the I>> common setting value. Currents

above these value are recorded and signalled individually. A trip signal is transmitted to the matrix as soon as corresponding T I>> time delays have elapsed.The drop-out value is ± 95% below the pick-up value.

The I> stage has an undervoltage stage that can be disabled. This stage maintains the pick-up signal for a settable seal-in time if the value falls below a settable threshold of the positive sequence component of the voltages after an overcurrent pick-up value. This will ensure that the 500-1 timer is sealed in, and will time out to trip the associated circuit breaker. If the voltage recovers before the seal in time has elapsed or if the undervoltage seal-in is blocked via a binary input-e.g. when the voltage transformer MCB trips or if the machine is tripped, the function will drop out immediately.

The seal-in logic operates separately for each phase. The first pickup of a phase overcurrent starts thetimer T-SEAL-IN.