ABB RELION REX640 Technical Manual page 812

Section 4
Protection functions
806
time calculation or integration starts immediately when the excitation level exceeds
the set Start value and the START output is activated.
The OPERATE output is activated when the cumulative sum of the integrator
calculating the overexcitation situation exceeds the value set by the inverse time
mode. The set value depends on the selected curve type and the setting values used.
The Minimum operate time and Maximum operate time settings define the minimum
operate time and maximum operate time possible for the IDMT mode. For setting
these parameters, a careful study of the particular IDMT curves is recommended.
The operation 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 START output for the IDMT curves. If the
excitation level drops below the Start value setting before the function operates, the
reset timer is activated and the START output resets immediately. If START reoccurs
during the reset time, the operation calculation is made based on the effects of the
period when START was previously active. This is intended to allow an operating
condition to occur in less time to account for the heating effects from the previous
active start period.
When START becomes active, the reset time is based on the following equation.
START DUR _

reset time
=

100

GUID-F852EE1A-3E58-48A8-8A1C-23898CC1A6F9 V1 EN
For the IDMT curves, when START is deactivated, the integral value calculated
during START 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 start time is adjusted, as
shown in Figure 437. The start 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 start time and integration are
cleared.

Cooling time
 ⋅

1MRS759142 C
(Equation 202)
REX640
Technical Manual