ABB RELION REX640 Technical Manual page 1134

Protection functions
Figure 635: Natural unbalance compensation. (a) Healthy condition when the natural
unbalance is recorded (b) Unbalance compensation during faulty conditions
The natural unbalance compensation for each phase is enabled based on the
settings
respectively. For example, if
current is not compensated. If
compensated unbalance current for phase A is calculated based on the equation.
I
CompUnb_A
I
CompUnb_A
I
Urb_A
I
NatUnb_A
The phasewise-compensated unbalance current amplitudes and angles
I_COM_AMPL_A, I_COM_ANGL_A, I_COM_AMPL_B, I_COM_ANGL_B, I_COM_AMPL_C
and I_COM_ANGL_C are available in the monitored data view.
The phase angles of the unbalance currents indicate the branch of a faulty element
in a capacitor bank. For an internal fuse capacitor bank, the element failure branch
location is determined based on the phase angle of the compensated unbalance
current.
Table 1077: Detection of element failure location for internal fuse capacitor bank
Name of the phase angle
I_COM_ANGL_A
I_COM_ANGL_A
Table continues on the next page
1134
Natural Comp Ena PhA , Natural Comp Ena PhB and Natural Comp Ena PhC
Natural Comp Ena PhA is set to "FALSE", the unbalance
I I
= −
Unb_A NatUnb_A
Phase A-compensated unbalance current
Phase A-measured unbalance current
Phase A-recorded natural unbalance current
Phase angle of unbalance cur-
rent
~+180°
~0°
Natural Comp Ena PhA is set to "TRUE", the
1MRS759142 F
(Equation 288)
Element failure branch loca-
Figure 634
tion
Phase A - Branch 1 or Phase A
- Branch 4
Phase A - Branch 2 or Phase A
- Branch 3
REX640
Technical Manual