GE C70, Instruction Manual

Page: 466 / 708

9-14 C70 Capacitor Bank Protection and Control System GE Multilin
9.4 SETTING EXAMPLE 9 APPLICATION OF SETTINGS
9
• Source 2 (tap 1) and source 3 (tap 2) are assigned with the VT banks and split window CT bank connected to the tap
point of two strings of the bank, providing a signal source for the voltage differential and phase unbalance functions.
The CT and VT connections shown in the figure above are assigned the following values in EnerVista UR Setup.
9.4.4 BANK UNBALANCE CALCULATIONS
The following values are used in unbalance calculations.
The impedance of one capacitor can:
(EQ 9.5)
The impedance of one capacitor element, with n = 6 capacitor elements per can:
(EQ 9.6)
The impedance of the top healthy capacitor string:
(EQ 9.7)
The impedance of the bottom capacitor can:
(EQ 9.8)
The total impedance of the healthy capacitor string:
(EQ 9.9)
The maximum rated line-to-neutral system voltage:
(EQ 9.10)
The maximum rated phase current of the healthy bank:
(EQ 9.11)
The maximum rated voltage across the healthy top section:
(EQ 9.12)
The maximum rated voltage across the healthy bottom section:
Z
C
c
V
C
2
Q
C
--------
11.62 V
( )
2
500 10
3
–
× vars
----------------------------------------- 270.05 Ω
= = =
Z
C
e
Z
C
c
n
-------
270.05 Ω
6
-----------------------
45.01
Ω
= = =
Z
C
s
Z
C
c
N × 270.05 Ω 7 × 1890.34 Ω
= = =
Z
C
b
V
CN
2
Q
CN
-----------
0.825 V ( )
2
0.167 var
----------------------------
4.08
Ω
= = =
Z
C
t
Z
C
s
Z
C
b
+
1890.34 Ω 4.08 Ω
+
1894.42 Ω
= = =
V
max
V
C
N
×
V
C
N ×
Z
C
s
------------------
Z
C
b
×
+
11620 V 7
×
11620 V 7 ×
1890.34
Ω
--------------------------------
4.08
Ω ×
+
81515.37 V
= = =
I
max
V
max
Z
C
t
2
⁄
--------------
81515.37 V
1894.92
Ω
2
⁄
----------------------------------
86.06 A
= = =
V
top
V
max
Z
C
s
×
Z
C
t
--------------------------
81515.37 V 1890.34
Ω ×
1894.92
Ω
----------------------------------------------------------------
81340.40 V
= = =