7SR18 Commissioning & Maintenance Guide
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3.4.3 IEC RESET
If the element is configured as an IEC characteristic, it may have an IEC (decaying) reset delay applied. If IEC
reset is selected for an IEC characteristic element, the reset will be instantaneous.
IEC reset times from operated condition to fully reset are as follows for zero applied current and Time multiplier
(TM) = 1.0. The reset curve characteristic type and TM is defined by the operating characteristic.
Curve Fully operated to reset with Zero current applied & TM=1 (seconds)
IEC-NI 9.7
IEC-VI 43.2
IEC-EI 58.2
IEC-LTI 80
Apply current in the following sequence, a) 2x setting for a time to ensure element operation, b) Zero current for
the reset time above (xTM), c) 2x setting for a time to ensure element operation. Check that the second operation
(c) is similar to the first (a) and in line with the expected operate time for the element at this current level.
Repeat the test with the reset time (b) reduced to 50 % of the previous value. Ensure that the second operate
time (c) is 50 % of the first (a) operate time.
3.4.4 ELEMENT BLOCKING
The 51c Overcurrent elements can be blocked by Binary Input Inhibit. This functionality should be checked.
Element BI Inhibits
51c
Operate
time
(expected)
Reset time
(calculated)
Operate time
(measured)
50% Reset
Time
(calculated)
50% Operate
time
(calculated)
50% Operate time
(measured)
First test (c) Second Test (c)
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