ABB RELION REX640 Technical Manual page 1028

Section 4
Protection functions
1022
The operation of CUBPTOC can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
I_A
I3P
I_UNB
BLOCK
GUID-32959F3A-CE55-4EE4-971E-BF01016C7F2D V1 EN
Figure 552: Functional module diagram
Natural unbalance Compensation
A standard double-Y-connected shunt capacitor bank configuration is shown in
Figure 553. 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.
GUID-FAAF7CDC-C015-4289-8E54-5E4AB0D3E3F9 V1 EN
Figure 553: 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.
Natural
Level
unbalance
compens-
detector 1
ation
Blocking
logic
Level
detector 2
1MRS759142 C
Timer
OPERATE
t
t
START
Alarm
ALARM
control
Technical Manual
REX640