Figure 355: Operating curve of "OvExt IDMT Crv2" based on the settings
specified in example 3. The two dots marked on the curve are referred to in
the text.
If the excitation level stays at 1.26, the operation occurs after 26360
milliseconds as per the marked dot in
of 1.4, the second dot in
, the curve "OvExt IDMT Crv2" gives 260
milliseconds as per Equation, but the
Minimum operate time setting limits
the operate time to 1000 milliseconds. The
Maximum operate time setting
limits the operate time to 1000000 milliseconds if the excitation level stays
between 1.1 and 1.16.
In general, however, the excitation level seldom remains
constant. Therefore, the exact operate times in any
inverse time mode are difficult to predict.
Example 4
In this case, the function operation is according to IDMT. The
Operating
curve type setting is selected as "OvExt IDMT Crv4". The corresponding
example settings for the IDMT curve operation are given as:
Start value =
110%,
Voltage Max Cont = 100%, Time multiplier = 5, Maximum operate time
= 3600000 milliseconds and
Constant delay = 800 milliseconds.
1MRS757644 H
Protection functions
620 series
Technical Manual
683
