5-138 L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALSYSTEM SETUP CHAPTER 5: SETTINGS5It 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 CThas 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 eachCT and VT input. For CT inputs, this is the nominal primary and secondary current. For VTs, this is the connection type, ratioand 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 elementsCT/VT modules automatically calculate all current and voltage parameters from the available inputs. Users must select thespecific input parameters to be measured by every element in the relevant settings menu. The internal design of theelement specifies which type of parameter to use and provides a setting for source selection. In elements where theparameter can be either fundamental or RMS magnitude, such as phase time overcurrent, two settings are provided. Onesetting specifies the source, the second setting selects between fundamental phasor and RMS.5.5.3.2 AC input actual valuesThe calculated parameters associated with the configured voltage and current inputs are displayed in the current andvoltage sections of actual values. Only the phasor quantities associated with the actual AC physical input channels displayhere. 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 onthe protected system. The 50DD function is used directly in some elements in the relay, for example VT Fuse Failuredetector or Fault Report. It can also be used to supervise current-based elements to prevent maloperation as a result ofthe 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 asfollows.
