BLOCK
OPERATE
I_UNB
Natural
unbalance
compens-
ation
START
ALARM
Level
detector 1
Level
detector 2
Blocking
logic
Alarm
control
t
Timer
t
I3P
I_A
Figure 628: Functional module diagram
Natural unbalance Compensation
A standard double-Y-connected shunt capacitor bank configuration is shown in
Figure 629
. The fundamental frequency component of an unbalance current is
measured on the common neutral connecting the two balanced parts of a shunt
capacitor bank, that is, between star point 1 and star point 2.
Figure 629: Double-Y-connected capacitor bank
The phase angle of the measured fundamental frequency component of the
unbalance current I_UNB is synchronized by using the phase current I_A as a
reference.
∠ = ∠ − ∠I I UNB I A
unb
_ _
(Equation 285)
In a three-phase star-connected capacitor bank circuit, there may be some amount
of natural unbalance current flowing through the neutral, which is primarily due
1MRS759142 F
Protection functions
REX640
Technical Manual
1121
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