GE L90 Instruction Manual page 96

5.1 OVERVIEW
additional features that operate on the individual currents, such as breaker failure). Given the flexibility of this approach, it
becomes necessary to add configuration settings to the platform to allow the user to select which sets of CT inputs will be
added to form the net current into the protected device. The internal grouping of current and voltage signals forms an inter-
nal source. This source can be assigned a specific name and becomes available to protection and metering elements in the
relay. Individual names can be given to each source to identify them for later use. For example, in the scheme shown
above, three different sources are be configured as inputs for separate elements:
Source 1: CT1 current, for the Breaker Failure 1 element and first current source for the Line Differential element
Source 2: CT2 current, for Breaker Failure 2 element and second current source for the Line Differential element
Source 3: the sum of the CT1 and CT2 currents for the distance function
In addition, two separate synchrocheck elements can be programmed to check synchronization between line voltage and
two different bus voltages (SRC3–SRC1 and SRC3–SRC2).
b) CT/VT MODULE CONFIGURATION
CT and VT input channels are contained in CT/VT modules. The type of input channel can be phase/neutral/other voltage,
phase/ground current, or sensitive ground current. The CT/VT modules calculate total waveform RMS levels, fundamental
frequency phasors, symmetrical components and harmonics for voltage or current, as allowed by the hardware in each
channel. These modules may calculate other parameters as directed by the CPU module.
A CT/VT module contains up to eight input channels, numbered 1 through 8. The channel numbering corresponds to the
module terminal numbering 1 through 8 and is arranged as follows: Channels 1, 2, 3 and 4 are always provided as a group,
hereafter called a "bank," and all four are either current or voltage, as are Channels 5, 6, 7 and 8. Channels 1, 2, 3 and 5, 6,
7 are arranged as phase A, B and C respectively. Channels 4 and 8 are either another current or voltage.
Banks are ordered sequentially from the block of lower-numbered channels to the block of higher-numbered channels, and
from the CT/VT module with the lowest slot position letter to the module with the highest slot position letter, as follows:
5
INCREASING SLOT POSITION LETTER -->
CT/VT MODULE 1
< bank 1 >
< bank 2 >
The UR platform allows for a maximum of three sets of three-phase voltages and six sets of three-phase currents. The
result of these restrictions leads to the maximum number of CT/VT modules in a chassis to three. The maximum number of
sources is six. A summary of CT/VT module configurations is shown below.
ITEM
CT/VT Module
CT Bank (3 phase channels, 1 ground channel)
VT Bank (3 phase channels, 1 auxiliary channel)
5-6
CT/VT MODULE 2 CT/VT MODULE 3
< bank 3 > < bank 5 >
< bank 4 > < bank 6 >
MAXIMUM NUMBER
L90 Line Differential Relay
2
8
4
5 SETTINGS
GE Multilin