ABB RELION REX640, Техническое руководство, Страница: 1152 / 1960

U
A
U
B
U
C
U
Neutral
U
0_T
Measured (by open
delta) or calculated
residual voltage
N
G
n
g
PT
Figure 644: 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
Figure 645
.
Operating signal
= − ⋅
−
U
U
n
U
U U
Neutral
N sr
Uo
N pr
o unb
_ _
Figure 645: Equation
U
Neutral
Measured shunt capacitor neutral voltage
U
o
Measured open delta voltage
U
unb
Natural unbalance compensation component
n
Uo
Voltage ratio of open delta VT
U
N_sr
Rated secondary voltage of neutral connected VT
U
N_pr
Rated primary voltage of neutral connected VT
The rated
Primary voltage and Secondary voltage for the neutral voltage channel
U
Neutral
, and for U
N_pr
and U
N_sr
are set in the global setting under Configuration >
Analog inputs > Voltage (Uo,VT).
The operating signal setting is given as multiple of the neutral VT rated
voltage.
In monitored data, xUn refers to neutral VT rated voltage.
4.12.5.7 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 in the impedances of the protected bank. The unbalance protection
responds to unbalances in the measured signals caused by changes in the
impedance of the capacitor bank.
In compensating unbalance protection, the operating signal compensates both the
inherent capacitor bank unbalance and the system unbalance. The method involves
measuring the residual voltage at the capacitor terminal side and at the neutral
Protection functions 1MRS759142 F
1152 REX640
Technical Manual