Section 4 1MAC309294-MB FProtection functions148 RER620Technical Manualcoil or the grounding resistor. This is the case for instance, when a directional ground-faultrelay is used in an MV-switching substation some kilometers from the HV/MV -substationin which the grounding facilities are located. Another example is whenHV/MV-substations are connected in parallel but located far from each other.It is easy to give the tripping sector such a width that all possible directions of theI 0-phasors of a faulty line are covered by one and the same sector. Thus, the problem ofsetting the characteristic angle according to the grounding status of the network is easilysolved. There is no need to change any settings when a Petersen coil or a grounding resistoris switched on or off. Auxiliary switches and other pieces of extra hardware are no longerrequired for ensuring the selectivity of the directional ground-fault protection.Figure 64: Extended operation area in directional ground-fault protection4.1.4.6 Measurement modesThe function operates on three alternative measurement modes: “RMS”, “DFT” and“Peak-to-Peak”. The measurement mode is selected with the Measurement mode setting.Table 166: Measurement modes supported by 67/51N and 67/50N stagesMax forward angleRCA=0°Current start valuePositiveoperationsectorNegativeoperationsector-Min forward angle0V0IMeasurement mode Supported measurement modes67/51N and 67/50N-1 67/50N-2RMS x xDFT x xPeak-to-Peak x xFor a detailed description of the measurement modes, see the Generalfunction block features section in this manual.
