ABB RELION REX640, Technical Manual, Page: 896 / 1960

Figure 500: 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 26.364 s as per
the marked dot in
Figure 500
. For the excitation level of 1.4, the second dot
in
Figure 500
, the curve "OvExt IDMT Crv2" gives 0.2636 s as per
Equation
249
, but the
Minimum operate time setting limits the operate time to 1.0 s.
The
Maximum operate time setting limits the operate
time to 1000 s 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
= 3600 s,
Constant delay = 0.8 s and Cooling time = 100 s.
Protection functions 1MRS759142 F
896 REX640
Technical Manual