5-116 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALPRODUCT SETUP CHAPTER 5: SETTINGS5If the broken-delta neutral voltage is not available to the relay, an approximation is possible by assuming the missing zero-sequence voltage to be an inverted voltage drop produced by the zero-sequence current and the user-specifiedequivalent zero-sequence system impedance behind the relay: V0 = –Z0 × I0. In order to enable this mode of operation, theFAULT REPORT 1 VT SUBSTITUTION setting is set to “I0”.The FAULT REP 1 SYSTEM Z0 MAG and FAULT REP 1 SYSTEM Z0 ANGLE settings are used only when the VT SUBSTITUTION settingvalue is “I0”. The magnitude is to be entered in secondary ohms. This impedance is an average system equivalent behindthe relay. It can be calculated as zero-sequence Thevenin impedance at the local bus with the protected line/feederdisconnected. The method is accurate only if this setting matches perfectly the actual system impedance during the fault.If the system exhibits too much variability, this approach is questionable and the fault location results for single-line-to-ground faults is trusted accordingly. Keep in mind that grounding points in the vicinity of the installation impact the systemzero-sequence impedance (grounded loads, reactors, zig-zag transformers, shunt capacitor banks, and so on).5.3.9 Oscillography5.3.9.1 MenuSETTINGS PRODUCT SETUP OSCILLOGRAPHYOscillography records contain waveforms captured at the sampling rate as well as other relay data at the point of trigger.Oscillography records are triggered by a programmable FlexLogic operand. Multiple oscillography records can be capturedsimultaneously.When EnerVista UR Setup creates a new settings file, a Smart defaults feature automatically enters a basic oscillographyconfiguration. The basic configuration changes the factory default values to make the number of samples per cycle 32,adds a selection of digital and analog channels that are often of interest, and adds a FlexLogic equation to triggeroscillography. Review and update this basic configuration as required for the application at hand.The NUMBER OF RECORDS is selectable, but the number of cycles captured in a single record varies considerably based onother factors, such as sample rate and the number of operational modules. There is a fixed amount of data storage foroscillography; the more data captured, the less the number of cycles captured per record. See the ACTUAL VALUES RECORDS OSCILLOGRAPHY menu to view the number of cycles captured per record. The following table provides sampleconfigurations with corresponding cycles/record. The minimum number of oscillographic records is three.For proper operation of the multi-ended fault locator, the nominal primary voltage is expected to appear identicalat all line terminals as seen from the nominal secondary voltage, VT ratio, and VT connection settings of the first87L source. OSCILLOGRAPHY NUMBER OF RECORDS:5Range: 1 to 64 in steps of 1 TRIGGER MODE:Automatic OverwriteRange: Automatic Overwrite, Protected TRIGGER POSITION:50%Range: 0 to 100% in steps of 1 TRIGGER SOURCE:OffRange: FlexLogic operand AC INPUT WAVEFORMS:16 samples/cycleRange: Off; 8, 16, 32, 64 samples/cycle DIGITAL CHANNELSSee below ANALOG CHANNELSSee below
