Toshiba GRD140 Instruction Manual

⎯ 19 ⎯6 F 2 S 0 7 5 82.1.2.2 Directional CharacteristicsFigure 2.1.12 illustrates the directional characteristic, with the forward operate zone shaded. Thereverse zone is simply a mirror image of the forward zone. The forward operate zone or reverseoperate zone is selectable by the scheme switch [OC-DIR], [EF-DIR], [SE-DIR] and [NC-DIR].As shown in Figure 2.1.13, each directional characteristic is composed of forward directionalcharacteristic, reverse directional characteristic and overcurrent thresholds.5 x Is10 x IsCACA + 30CA + 60CA - 30CA - 60CA - 180ForwardOperateZoneBoundary of Operation(lagging)Boundary of Operation(leading)ReverseOperateZoneCA + 90CA - 90CA: Characteristic angleCA - 1805 x Is10 x IsCACA + 30CA + 60CA - 30CA - 60CA - 180ForwardOperateZoneBoundary of Operation- 87.5° (lagging)Boundary of Operation+87.5° (leading)ReverseOperateZoneCA + 90CA - 90CA: Characteristic angle(a) Characteristic of OC, EF and NOC (b) Characteristic of SEFFigure 2.1.12 Directional Operate CharacteristicFigure 2.1.13 Directional elementPolarising signals of directional elements are shown in Figure 2.1.14. Polarisation for directionalphase overcurrent element OC is achieved by the 90° quadrature method, whereby each current’sphase angle is compared with the phase to phase voltage between the other two phases. Since thevoltage inputs to the relay will normally be connected phase to neutral, the polarising phase tophase voltages are derived internally. The polarizing negative sequence voltage is also derivedinternally. The polarizing zero sequence voltage is derived from a residual voltage or internallydepending on the model. Direction is determined in each case by measuring the phase angle of thecurrent with respect to a suitable polarising quantity. Table 2.1.2 summarises the current inputsand their respective polarising signals. For details of the relationship between directional earthfault protection and power system earthing, see Appendix B.VpolI0Forwardθ+θ: lead angle−θ: lag angleθ: Characteristic angleReverse Stage4123Directional (Forward)Directional (Reverse)Overcurrent (1-4 stage)&&∗∗1-4Forward∗∗1-4Reverse(0 ≤ θ setting ≤ -95)(95 ≥ θ setting > 0)(Note) NOC provides stage 1 and 2 only.

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