CHAPTER 5: SETTINGS
SYSTEM SETUP
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
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5
equipment. They replace the traditional contact inputs and outputs located at the relay to virtually eliminate copper
wiring.
•
Configure shared inputs and outputs as required for the application's functionality. Shared inputs and outputs are
distinct binary channels that provide high-speed protection quality signaling between relays through a Brick.
For additional information on how to configure a relay with a process bus module, see the HardFiber Process Bus System
Instruction Manual.
5.5 System setup
5.5.1 AC inputs
5.5.1.1 Current banks
SETTINGS
SYSTEM SETUP
AC INPUTS
CURRENT BANK F1(F5)
Four 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} 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
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:
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F1: CT bank with 500:1 ratio
•
F5: CT bank with 1000:1 ratio
The following rule applies:
SRC1 = F1 + F5
Eq. 5-6
1 pu is the highest primary current. In this case, 1000 is entered and the secondary current from the 500:1 ratio CT is
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).
CURRENT BANK F1
PHASE CT F1
PRIMARY: 1
A
Range: 1 to 65000 A in steps of 1
PHASE CT F1
SECONDARY: 1 A
Range: 1 A, 5 A
GROUND CT F1
PRIMARY: 1
A
Range: 1 to 65000 A in steps of 1
GROUND CT F1
SECONDARY: 1 A
Range: 1 A, 5 A
