ABB RELION REX640 - Page 892

t s d
k
M
( )
.
( )
= +
−
0 18
1
2
(Equation 250)
t(s) Operate time in seconds
d
Constant delay setting in milliseconds
M Excitation value (U/f ratio or volts/hertz) in pu
k Time multiplier setting
Figure 498: Operating time curves for the overexcitation IDMT curve 4 ("OvExt IDMT
Crv4") for different values of the Time multiplier setting when the Constant delay is
800 milliseconds
The activation of the OPERATE output activates the BLK_RESTART output.
If the excitation level increases above the set value when BLK_RESTART is active, the
OPERATE output is activated immediately.
If the excitation level increases above the set value when BLK_RESTART is not active
but COOL_ACTIVE is active, the OPERATE output is not activated instantly. In this
case, the remaining part of the cooling timer affects the calculation of the operate
timer as shown in
Figure 499 . This compensates for the heating effect and makes
the overall operate time shorter.
Protection functions
1MRS759142 F
892 REX640
Technical Manual