GE L30 Instruction Manual page 299

CHAPTER 5: SETTINGS SYSTEM SETUP
It is possible to select the sum of all CT combinations. The first channel displayed is the CT to which all others are referred.
For example, the selection "F1+F5" indicates the sum of each phase from channels "F1" and "F5," scaled to whichever CT
has the higher ratio. Selecting "None" hides the associated actual values.
The approach used to configure the AC sources consists of several steps; first step is to specify the information about each
CT and VT input. For CT inputs, this is the nominal primary and secondary current. For VTs, this is the connection type, ratio
and nominal secondary voltage. Once the inputs have been specified, the configuration for each source is entered,
including specifying which CTs are summed together.
5.5.3.1 User selection of AC parameters for comparator elements
CT/VT modules automatically calculate all current and voltage parameters from the available inputs. Users must select the
specific input parameters to be measured by every element in the relevant settings menu. The internal design of the
element specifies which type of parameter to use and provides a setting for source selection. In elements where the
parameter can be either fundamental or RMS magnitude, such as phase time overcurrent, two settings are provided. One
setting specifies the source, the second setting selects between fundamental phasor and RMS.
5.5.3.2 AC input actual values
The calculated parameters associated with the configured voltage and current inputs are displayed in the current and
voltage sections of actual values. Only the phasor quantities associated with the actual AC physical input channels display
here. All parameters contained within a configured source are displayed in the sources section of the actual values.
5.5.3.3 Disturbance detectors (internal)
The disturbance detector (ANSI 50DD) element is a sensitive current disturbance detector that detects any disturbance on
the protected system. The 50DD function is used directly in some elements in the relay, for example VT Fuse Failure
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detector or Fault Report. It can also be used to supervise current-based elements to prevent maloperation as a result of
the wrong settings or external CT wiring problem. A disturbance detector is provided for each source.
The 50DD function responds to the changes in magnitude of the sequence currents. The disturbance detector logic is as
follows.
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-121