ABB RELION REX640 Technical Manual page 1041

1MRS759142 C
REX640
Technical Manual
Branch 1
I_UNB_A
Branch 3
GUID-1289B91B-EEFC-4FD4-B2A3-88BEB56350B7 V1 EN
Figure 558: H-Bridge-connected capacitor bank
The phase angles of three-phase measured unbalance currents are synchronized using
the phase current I_A as reference. The phase-A unbalance current phase angle can be
calculated with the equation.
I I_UNB_A
∠ = ∠ − ∠
Unb_A
GUID-CF2CE17A-3B38-43BB-A6DA-CEACD2EBEF2A V1 EN
A three-phase H-bridge-connected capacitor bank circuit may have some amount of
natural unbalance current flowing through the common points of H-bridge, which
may primarily be due to capacitor manufacturing tolerances. Therefore, the natural
unbalance current must be compensated for before using the measured unbalance
current for 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/HCUBPTOC. The natural unbalance currents are recorded
for all the phases at the same time by setting command Record unbalance to "Record
all phases" or each natural unbalance current can be recorded separately for individual
phases by setting command Record unbalance to "Record phase A" or "Record phase
B" or "Record phase C". By selecting Record unbalance with value "Record", the
measured three-phase unbalance currents (
natural unbalance currents for each phase respectively and stored as a reference. The
amplitude and angle of the phasewise-recorded natural unbalance currents
I_NAT_AMPL_A, I_NAT_ANGL_A, I_NAT_AMPL_B, I_NAT_ANGL_B,
I_NAT_AMPL_C and I_NAT_ANGL_C are available in the monitored data view.
Once a natural unbalance current is recorded, the phasewise natural unbalance current
is subtracted from the corresponding phase-measured unbalance current (
further executions of the function to obtain the compensated unbalance current
I
( ) .
CompUnb
Branch 2
I_UNB_B
Branch 4
I_A
I
Unb A Unb B Unb C _
Section 4
Protection functions
I_UNB_C
, I , I
) are considered the
_ _
(Equation 242)
) during
I
Unb
1035