ABB RELION REX640 - Page 1122

to capacitor manufacturing tolerances. The natural unbalance current must be
compensated for before using the measured unbalance current for the function
operation. The natural unbalance current needs to be recorded when there is no
fault in the capacitor banks, and it is initiated through the command Record
unbalance , available under menu path Control> CUBPTOC. By selecting Record
unbalance with value “Record”, the measured unbalance current
I
Unb
is considered
as the natural unbalance current
I NatUnb
and is stored as a reference. The amplitude
and angle of the recorded natural unbalance current I_AMPL_NAT and I_ANGL_NAT
are available in the monitored data view.
Once the natural unbalance current is recorded during further executions of the
function, the natural unbalance current is subtracted from the measured unbalance
current
I
Unb
to obtain the compensated unbalance current
I
CompUnb
as shown in
Figure 630 .
Figure 630: Natural unbalance compensation. (a) Healthy condition when the natural
unbalance is recorded (b) Unbalance compensation during faulty conditions
The natural unbalance current compensation is enabled using the setting Natural
Comp Enable . If Natural Comp Enable is set to “FALSE”, the unbalance current is not
compensated. If Natural Comp Enable is set to “TRUE”, the compensated unbalance
current is calculated based on the equation.
I I I
CompUnb Unb NatUnb
= −
(Equation 286)
The amplitude I_AMPL_COMP and the angle I_ANGL_COMP of the compensated
unbalance current
I
CompUnb
are available in the monitored data view.
Protection functions
1MRS759142 F
1122 REX640
Technical Manual