1MAC050144-MB C
Section 4
Protection functions
615 series ANSI
253
Technical Manual
When the fault disappears, the reset time can be calculated:
Equation 7
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 119 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.
Figure 119:
An example of a delayed reset in the inverse time characteristics. When
the pickup becomes active during the reset period, the trip time counter
continues from the level corresponding to the drop-off (reset time = 0.50 ·
Cooling time).
Overexcitation IDMT curves 1, 2 and 3
The base equation for the IDMT curves "OvExt IDMT Crv1", "OvExt IDMT Crv2" and
"OvExt IDMT Crv3" is:
time
Cooling
DUR
PICKUP
time
reset
100
_
PICKUP
Drop-off
PICKUP
Reset
reset time
Trip level
Inverse time
counter
time
50%
100%
PICKUP
resets
Содержание 615 Series ANSI
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