DOC. MIE91093 Rev. 1.34 Page 63 of 145
1.8.3. Voltage threshold and drop-off
We start from a situation where:
. Amplitudes are different;
. Phase is 0°;
. Frequency is the same (the mains).
From this, we will modify an amplitude, until the relay trips:
this is the voltage threshold. There are two thresholds, above
and below VN: the test will be performed first with V2 > V1,
and then with V2 < V1.
. Press ON, and adjust V1 to VN.
. Press OFF, and adjust the value of V2 to a value greater than
VN, that is outside the permission (for instance, 110 V).
. Now, press ON again, check that the relay is not tripped, and
slowly reduce the voltage until the relay trips: at this moment,
confirm save results pressing the multi-function knob, and
proceed: the high voltage threshold V> is found.
NOTE: Stored values are the voltages as relay trips. This
corresponds to the relay threshold only if the voltage did not
change very much while the relay relay timing T1 elapsed;
soothe voltage should be changed quite slowly. 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 V>. From the voltage
above, slowly increase it; as the relay resets, confirm save
results pressing the multi-function knob, and proceed.
NOTE: stored values are the voltages as the relay resets. This
corresponds to the relay drop-off only if the voltages did not
change very much while the relay timing elapsed; however,
reset timing is usually very short, so the voltage does not
change very much at release, and the measurement is
accurate.
. Now, repeat the procedure for V<. The starting voltage (pre-
fault and fault) will be less than VN (for instance, 90 V); the
threshold and drop-off for V< are found.
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