System Setup; Ac Inputs - GE C70 Instruction Manual

SYSTEM SETUP

5.5 System setup

5.5.1 AC inputs

5.5.1.1 Current banks
SETTINGS  SYSTEM SETUP  AC INPUTS  CURRENT BANK F1(U5)
 CURRENT BANK F1

Six banks of phase and ground CTs can be set, where the current banks are denoted in the following format (X represents
the module slot position letter):
Xa, where X = {F, M, U} and a = {1, 5}
See the Introduction to AC Sources section at the beginning of this chapter for details.
These settings are critical for all features that have settings dependent on current measurements. When the relay is
5
ordered, the CT module must be specified to include a standard or sensitive ground input. As the phase CTs are connected
in wye (star), the calculated phasor sum of the three phase currents (IA + IB + IC = neutral current = 3Io) is used as the input
for the neutral overcurrent elements. In addition, a zero-sequence (core balance) CT which senses current in all of the
circuit primary conductors, or a CT in a neutral grounding conductor can also be used. For this configuration, the ground
CT primary rating must be entered. To detect low level ground fault currents, the sensitive ground input can be used. In this
case, the sensitive ground CT primary rating must be entered. See chapter 3 for more details on CT connections.
Enter the rated CT primary current values. For both 1000:5 and 1000:1 CTs, the entry would be 1000. For correct operation,
the CT secondary rating must match the setting (which must also correspond to the specific CT connections used).
The following example illustrates how multiple CT inputs (current banks) are summed as one source current. Given the
following current banks:
• F1: CT bank with 500:1 ratio
• F5: CT bank with 1000:1 ratio
• M1: CT bank with 800:1 ratio
The following rule applies:
1 pu is the highest primary current. In this case, 1000 is entered and the secondary current from the 500:1 and 800:1 ratio
CTs are adjusted to that created by a 1000:1 CT before summation. If a protection element is set up to act on SRC 1
currents, then a pickup level of 1 pu operates on 1000 A primary.
The same rule applies for current sums from CTs with different secondary taps (5 A and 1 A).
5.5.1.2 Voltage banks
SETTINGS  SYSTEM SETUP  AC INPUTS  VOLTAGE BANK F5(U5)
 VOLTAGE BANK F5

5-140
PHASE CT F1

PRIMARY: 1 A
PHASE CT F1

SECONDARY: 1 A
GROUND CT F1

PRIMARY: 1 A
GROUND CT F1

SECONDARY: 1 A
SRC 1 = F1 + F5 + M1
PHASE VT F5

CONNECTION: Wye
PHASE VT F5

SECONDARY: 66.4 V
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Range: 1 to 65000 A in steps of 1
Range: 1 A, 5 A
Range: 1 to 65000 A in steps of 1
Range: 1 A, 5 A
Range: Wye, Delta
Range: 25.0 to 240.0 V in steps of 0.1
Eq. 5-6