Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.12.5.6
1054
U
A
U
B
U
C
N
U
G
PT
GUID-FA9D2501-A304-46B4-970B-6CAA6B430DD4 V1 EN
Figure 567: Ungrounded SCB
The operating signal for the compensated neutral voltage unbalance in per unit with
reference to the neutral side of an ungrounded SCB is as indicated in
U
Neutral
Operating signal =
U
N _
GUID-FA6C3817-E69C-461F-8067-1EEF2FBBB8CC V1 EN
Measured shunt capacitor neutral voltage
U
Neutral
Measured open delta voltage
U
o
Natural unbalance compensation component
U
unb
n Voltage ratio of open delta VT
Uo
U Rated secondary voltage of neutral connected VT
N_sr
U Rated primary voltage of neutral connected VT
N_pr
The rated Primary voltage and Secondary voltage for the neutral voltage channel
U , and for U and U
Neutral N_pr
Analog inputs/Voltage (Uo,VT).
The operating signal setting is given as multiple of the neutral VT
rated voltage.

Application

Shunt capacitor banks are provided with an unbalance protection function which is
mainly used to detect problems within capacitor units using the presumed symmetry
U
0_T
Measured (by open
delta) or calculated
residual voltage
n
Neutral
g
n
Uo
U U
o unb
− ⋅
−
U
sr N _ pr
are set in the global setting under Configuration/
N_sr
1MRS759142 C
Equation 247.
(Equation 247)
REX640
Technical Manual