GE UR Series C70 Instruction Manual page 429

10 APPLICATION OF SETTINGS
V
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 Z
=
C
The voltage at the tap in the section with one failed capacitor element in the string:
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, in per-unit
values is:
V
( )
diff tap
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
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.
Table 10–1: UNBALANCE VALUES FOR MAXIMUM SYSTEM CONDITIONS
n s sf
Z Z
f
C C
1894.42 Ω 1894.42 Ω
0
1894.42 Ω 1849.41 Ω
1
1894.42 Ω 1804.40 Ω
2
1894.42 Ω 1759.39 Ω
3
1894.42 Ω 1714.38 Ω
4
1894.42 Ω 1669.38 Ω
5
1894.42 Ω 1624.37 Ω
6
1894.42 Ω 1579.36 Ω
7
1894.42 Ω 1534.35 Ω
8
1894.42 Ω 1489.34 Ω
9
1894.42 Ω 1444.34 Ω
10
GE Multilin
b
×
V Z 81515.37 V 4.08 Ω
max C
= -------------------------- = ------------------------------------------------------- -
bottom
t
Z
C
V
81340.40 V
top
K
= ------------------ - = ------------------------------ -
tap
V 175.37 V
bottom
e b
( × )
N n n Z 45.01Ω
– + =
C f C
b
×
81515.37 V 4.08 Ω
V Z
max C
V
= -------------------------- = ------------------------------------------------------- -
tap2
sf
Z
C
× ×
V N n
( ) 81335.74 V 7
f top
= ---------------------------------------------- - = --------------------------------------------------------------- -
× ( × )
V N n – n 81340.40 V
top f
×
V K V
–
175.374 V 1 179.64 V
tap1 tap tap2
= =
-------------------------------------------------- - ------------------------------------------------------------------ -
VT
( )
nom tap
×
– K V
( ) 175.374 V 463.8194 179.64 V
f top string tap2
=
---------------------------------------------------------------------------------------- -
VT
( )
nom bus
V
81515.37 V
max max
– --------------------------- - = -------------------------------------- -
s 1845.33Ω 50
×
CT Z CT
tap C tap
V V
tap1 tap2
175.37 V 175.37 V
175.37 V 179.64 V
175.37 V 184.12 V
175.37 V 188.83 V
175.37 V 193.79 V
175.37 V 199.01 V
175.37 V 204.52 V
175.37 V 210.35 V
175.37 V 216.52 V
175.37 V 223.07 V
175.37 V 230.02 V
C70 Capacitor Bank Protection and Control System
×
= 175.37 V
1984.42Ω
463.8194
=
f
× ( × ) 4.08 Ω
7 6 1 1849.41Ω
– + =
×
179.64 V
=
4.08 Ω
× ×
6
= 1.024 pu
× ( × )
7 6 – 1
×
–
= 0.0249 pu
171.59 V
×
–
79674.34 V
81515.37 V
– -------------------------------------- - =
× ×
1890.34Ω 50
V OV V
top diff tap
81340.00 V 1.000 pu 0.0000 pu
81335.73 V 1.024 pu 0.0249 pu
81331.25 V 1.050 pu 0.0510 pu
81326.54 V 1.077 pu 0.0785 pu
81321.58 V 1.105 pu 0.1074 pu
81316.36 V 1.135 pu 0.1379 pu
81310.85 V 1.167 pu 0.1701 pu
81305.02 V 1.200 pu 0.2041 pu
81298.85 V 1.235 pu 0.2401 pu
81292.30 V 1.273 pu 0.2783 pu
81285.35 V 1.313 pu 0.3188 pu
10.4 SETTING EXAMPLE
(EQ 10.13)
(EQ 10.14)
= 1:
(EQ 10.15)
(EQ 10.16)
(EQ 10.17)
(EQ 10.18)
= 0.0249 pu
(EQ 10.19)
0.0209 pu
(EQ 10.20)
V I
( ) ( )
diff string unbal
0.0000 pu 0.0000 pu
0.0249 pu 0.0209 pu
0.0510 pu 0.0429 pu
0.0785 pu 0.0660 pu
0.1074 pu 0.0904 pu
0.1379 pu 0.1160 pu
0.1701 pu 0.1431 pu
0.2041 pu 0.1717 pu
0.2401 pu 0.2020 pu
0.2783 pu 0.2341 pu
0.3188 pu 0.2682 pu
10-15
10