ABB RELION REX640 Technical Manual page 813

1MRS759142 C
REX640
Technical Manual
GUID-616D6E96-3679-4FB9-86DB-DCF20A10639D V1 EN
Figure 437: An example of a delayed reset in the inverse time characteristics.
When the start becomes active during the reset period, the operate
time counter continues from the level corresponding to the drop-off
(reset time = 0.50 · Cooling time)
Overexcitation IDMT curves 1, 2 and 3
The base equation for the IDMT curves "OvExt IDMT Crv1", "OvExt IDMT Crv2"
and "OvExt IDMT Crv3" is:
ak b 100 M
 + − 
 
c
t s e
( ) = 60
 
⋅
GUID-368D8558-6F96-4C4C-80D8-063EFF6DF122 V1 EN
t(s) Operate time in seconds
M Excitation level (U/f ratio or volts/hertz) in pu
Time multiplier setting
k
The constant "60" in
Table 767: Parameters a, b and c for different IDMT curves
Operating curve type
a
setting
OvExt IDMT Crv1 2.5
OvExt IDMT Crv2 2.5
OvExt IDMT Crv3 2.5
Protection functions
Equation converts time from minutes to seconds.
b
115.00
113.50
108.75
Section 4
(Equation 203)
c
4.886
3.040
2.443
807