5-210 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUALGROUPED ELEMENTS CHAPTER 5: SETTINGS5Figure 5-106: Neutral directional voltage-polarized characteristicsNEUTRAL 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 user can useeither the zero-sequence voltage V_0 calculated from the phase voltages, or the zero-sequence voltage suppliedexternally 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 voltage source(such as broken delta connected secondary of VTs).The zero-sequence voltage V_0 must be greater than 0.02 pu to be validated for use as a polarizing signal.Additionally, when offset impedance is applied and zero-sequence current is above 0.2 pu, compensated zero-sequence voltage -V_0 + Z_offset x I_0 has to be above 0.02 pu in order to discriminate fault direction; otherwisewhen zero-sequence current is less than 0.2 pu, -V_0 is then used as the polarizing signal. If the polarizing signal isinvalid, 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 neutral pointof an adequate local source of ground current. The ground current must be greater than 0.05 pu to be validated as apolarizing signal. If the polarizing signal is not valid, neither forward nor reverse indication is given. In addition, thezero-sequence current (I_0) must be greater than the PRODUCT SETUP DISPLAY PROPERTIES CURRENT CUT-OFFLEVEL 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 current as apolarizing source, ensure that a reversal of the ground current does not occur for a high-side fault. Assume that the
