GE C70 Instruction Manual page 453

9 APPLICATION OF SETTINGS
V
The maximum rated voltage across the healthy bottom section:
The voltage distribution factor for the healthy perfectly balanced bank for the 87V-2 and 87V-3 elements:
The impedance of the string for the failed capacitors elements (for one failed element, n
sf
Z
=
C
The voltage at the tap in the section with one failed capacitor element in the string:
The voltage of the top section with one capacitor element failed:
The overvoltage at the affected capacitors with one capacitor element failed:
OV
The differential voltage between two taps with one failed capacitor element in the upper string, assuming K = 1 for 87V-1, in
per-unit values is:
V

diff tap
The differential voltage between the bus voltage and the tap with one failed capacitor element in the upper string, assuming
K = 1, for 87V-3 in per-unit values is:
V
=
 
diff string
The unbalance current in the window type CT between two strings with one failed capacitor element in the upper string:
V
---------------------------- -
I
=
unbal
sf
Z
C
The following table summarizes the calculated values for the number of failed capacitors used to set the protection ele-
ments.
GE Multilin
s

V Z
81515.37 V 1890.34
max C
-------------------------- --------------------------------------------------------------- -
= =
top
1894.92
t
Z
C
b

V Z
81515.37 V 4.08 
max C
-------------------------- ------------------------------------------------------- -
V
= =
bottom
t
Z
C
V
81340.40 V
top
------------------ - ------------------------------ -
K
= =
tap
V 175.37 V
bottom
e b
  
Z N n n Z 45.01
– + =
C f C
b

V Z
81515.37 V 4.08 
max C
V -------------------------- ------------------------------------------------------- -
= =
tap2
sf
Z
C
V V
=
top max
 
V N n
81335.74 V 7
 
f top
---------------------------------------------- - --------------------------------------------------------------- -
= =
   
V N n n 81340.40 V
–
top f

V 1 V
– 175.374 V 1
tap1 tap2
= ------------------------------------------ - = ------------------------------------------------------------------ -

VT
 
nom tap

V K V
–
175.374 V 463.8194
 
f top tap tap2
----------------------------------------------------- = ---------------------------------------------------------------------------------------- -
VT
 
nom bus
V
81515.37 V
max max
--------------------------- - -------------------------------------- -
– =
s 1845.33 50
 
CT Z CT
tap C tap
C70 Capacitor Bank Protection and Control System

81340.40 V
=

175.37 V
=
1894.92
463.8194
=
f
    4.08 
7 6 1 1849.41
– + =

179.64 V
=
1849.91 
V
–
tap2
 
6
1.024 pu
=
   
7 6 1
–

179.64 V
–
0.0249 pu
=
171.59 V

179.64 V
–
79674.34 V
81515.37 V
-------------------------------------- -
–
 
1890.34 50
9.4 SETTING EXAMPLE
(EQ 9.12)
(EQ 9.13)
(EQ 9.14)
= 1:
(EQ 9.15)
(EQ 9.16)
(EQ 9.17)
(EQ 9.18)
(EQ 9.19)
0.0249 pu
(EQ 9.20)
=
0.0209 pu
(EQ 9.21)
=
9
9-15