ABB RELION 620 Series Technical Manual page 307

1MAC504801-IB E
620 series ANSI
Technical Manual
The tripping time of the function block can vary much between different
operating curve types even if other setting parameters for the curves were
not changed.
Once activated, the timer activates the PICKUP output for the IDMT curves. If the
excitation level drops below the Pickup value setting before the function trips, the reset
timer is activated. If the fault reoccurs during the reset time, the tripping calculation is
made based on the effects of the period when PICKUP was previously active. This is
intended to allow a tripping condition to occur in less time to account for the heating
effects from the previous active pickup period.
When the fault disappears, the reset time can be calculated:
GUID-14537CFF-A8C8-49DF-A0D3-02FF269FE516 V1 EN
For the IDMT curves, when the fault disappears, the integral value calculated during
PICKUP is continuously decremented by a constant that causes its value to become zero
when the reset time elapses during the reset period. If a fault reoccurs, the integration
continues from the current integral value and the pickup time is adjusted, as shown in
Figure 136. The pickup time becomes the value at the time when the fault dropped off
minus the amount of reset time that occurred. If the reset period elapses without a fault
being detected, the saved values of the pickup time and integration are cleared.
Section 4
Protection functions
(Equation 9)
301