GE Multilin F60 Feeder Protection System 5-1755 SETTINGS 5.6 GROUPED ELEMENTS5The forward-looking function is designed to be more secure as compared to the reverse-looking function, and therefore,should be used for the tripping direction. The reverse-looking function is designed to be faster as compared to the forward-looking function and should be used for the blocking direction. This allows for better protection coordination.The above bias should be taken into account when using the neutral directional overcurrent element to directionalize otherprotection elements.Figure 5–76: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS• NEUTRAL DIR OC1 POLARIZING: This setting selects the polarizing mode for the directional unit.– If “Voltage” polarizing is selected, the element uses the zero-sequence voltage angle for polarization. The usercan use either the zero-sequence voltage V_0 calculated from the phase voltages, or the zero-sequence voltagesupplied externally as the auxiliary voltage V_X, both from the NEUTRAL DIR OC1 SOURCE.The calculated V_0 can be used as polarizing voltage only if the voltage transformers are connected in Wye. Theauxiliary voltage can be used as the polarizing voltage provided SYSTEM SETUP AC INPUTS VOLTAGE BANK AUXILIARY VT CONNECTION is set to “Vn” and the auxiliary voltage is connected to a zero-sequence voltagesource (such as broken delta connected secondary of VTs).The zero-sequence (V_0) or auxiliary voltage (V_X), accordingly, must be greater than the VOLTAGE CUTOFFLEVEL setting specified in the PRODUCT SETUP DISPLAY PROPERTIES menu to be validated for use as a polariz-ing signal. If the polarizing signal is invalid, neither forward nor reverse indication is given.– If “Current” polarizing is selected, the element uses the ground current angle connected externally and configuredunder NEUTRAL OC1 SOURCE for polarization. The ground CT must be connected between the ground and neutralpoint of an adequate local source of ground current. The ground current must be greater than 0.05 pu to be vali-dated as a polarizing signal. If the polarizing signal is not valid, neither forward nor reverse indication is given. Inaddition, the zero-sequence current (I_0) must be greater than the PRODUCT SETUP DISPLAY PROPERTIES CURRENT CUT-OFF LEVEL setting value.For a choice of current polarizing, it is recommended that the polarizing signal be analyzed to ensure that a knowndirection is maintained irrespective of the fault location. For example, if using an autotransformer neutral currentas a polarizing source, it should be ensured that a reversal of the ground current does not occur for a high-sidefault. The low-side system impedance should be assumed minimal when checking for this condition. A similar sit-uation arises for a wye/delta/wye transformer, where current in one transformer winding neutral may reverse whenfaults on both sides of the transformer are considered.827805A1.CDRVAG(reference)VBGVCG–3I_0 line3I_0 lineECA line–ECA lineLALALALAECAFWD LAlineFWD OperatingRegionREV OperatingRegionFWD LAlineREV LAlineREV LAline–3V_0 line3V_0 line
