Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
9.11.2.1
MINIMUM TIME DELAY
Each curve can be configured with Minimum Operating Time Limit. This means that the selected
curve is complemented with a fixed time portion so that regardless of the current magnitude, no trip
can be made faster than the set minimum time. The Minimum Operating Time is set as the parameter
Fixed Time.
Figure 9-34. Minimum Operating Time for time overcurrent curve
The Minimum Operating Time setting is not allowed to be larger than the curve’s operating time at 1.5
x pick-up. If this is the case, the fixed time setting is ignored and the operating time at this threshold is
used as Minimum Operating Time. This is illustrated in the figure below.
Figure 9-35. Minimum Operating Time when set Fixed Time exceeds curve time delay at 1.5 x pick-up.
Note. It is important to realize that while the curves are defined for up to 20 times the input current
(which is the set pick-up) it is not always possible to guarantee this range. The saturation limitation for
the current channels are 160 phase-ground. Considering this limitation, the ‘times pick-up’ where the
curves are valid is a function of the setting:
If
20
160
>
SetPU
A
the curve is guaranteed in it’s entire range (up to 20 times pick-up).
If
20
160
<
SetPU
A
the curve is guaranteed up to the actual multiple of the se pick-up of 160 A. For
example, an overcurrent element set with a pick-up of 40 A would follow the curve for up to 160/40 =
4 times pick-up
When a current larger than 20 times pickup is applied to the relay, the trip time will be equal to that
for 20 times.
August 1, 2009
9-39
973.334.3100
