Source Assignment - GE C70 Instruction Manual

CHAPTER 8: APPLICATION OF SETTINGS
The VT channels are connected as follows:
• The type 8L CT/VT module F5 to F7 three-phase VT channels are connected to the bus side three-phase VTs with a
138 / 0.115 kV ratio
• The type 8V CT/VT module M1 to M3 and M5 to M7 three-phase VT channels are connected to two tap VTs with a
1.25 / 0.25 kV ratio. The nominal voltage is calculated below for normal bank conditions and a nominal system voltage
of 138 kV (see impedance calculations the following sub-section).
The nominal bus phase VT voltage is:
The nominal tap VT voltage is:
Therefore, the tap VT secondary voltage is set as:
Where the VT ratio N is calculated as:
tap(VT)
The following settings are applied in the EnerVista UR Setup software.

8.4.3 Source assignment

The following sources must be assigned for the protection functions indicated:
• Source 1 (bus) is assigned with CT and VT banks connected to the bus, providing a signal source for overcurrent, phase
current unbalance, overvoltage, and undervoltage functions
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
13800
V = ------------- -
tap bus ( )
3
b
138000 Z ×
C
V = ---------------------------- =
tap nominal ( )
t
×
3 Z
C
V
tap nominal (
V = ---------------------------- -
tap secondary ( )
N
tap VT ( )
125 kV
N = ---------------- -
tap VT ( )
0.25 kV
= 79674.34 V
13800 × 4.08
------------------------------ - = 171.41 V
3 1894.42 ×
171.41 V
)
= ------------------- - = 34.28 V
5
= 5
SETTINGS EXAMPLE
Eq. 8-1
Eq. 8-2
Eq. 8-3
Eq. 8-4
8
8-13