I>> Threshold And Drop-Off - ISA T1000 PLUS User Manual

DOC. MIE91093 Rev. 1.34 Page 20 of 145
measurement can be found if the starter contact is available.
If threshold measurement was not good because you were
moving too fast, do not confirm test results and repeat the
test.
Next, we find the drop-off threshold for I>.
From the trip current above, slowly decrease the current; as
the relay resets, save test result.
NOTE: stored value is the current as the relay resets; as reset
timing is usually very short, current does not change very
much at drop-off, and the measurement is accurate.
1.1.4. I>> Threshold and drop-off
The second session is finding threshold I>>. The problem is
that the test result criterion is no more to find the limit
between no trip and trip; it is instead to find the limit between
two different timings: what we have shown as t>, for currents
less than I>>, and t>> for currents more than I>>. There are
many ways to perform the test; we suggest taking advantage
of the Timed generation option, as follows.
. Start from a current more than I>; select ON+TIME, and
check for time response. Take note of the timing t>. Compute
tmax as 80% of t>.
. Set the Timed test, as follows.
Test control > Fault injection > Timed > tmax (RET)
. Select ON+TIME, and start the test: the test goes OFF with
no message. Slowly increase the test current, until the relay
trips within tmax: this is the threshold; pressing the multi-
function knob tripping values can be saved.
NOTE: stored value is the current as the relay trips. This
corresponds to the relay threshold only if the current did not
change very much while the relay timing elapsed; however,
for this threshold the timing is short, so the measurement is
accurate.
Next, we find the drop-off threshold for I>> NOTE: this
parameter can be found only if there is a separate trip for the