GE Multilin B30 Bus Differential System 9-119 APPLICATION OF SETTINGS 9.5 BUS DIFFERENTIAL SETTINGS99.5BUS DIFFERENTIAL SETTINGS 9.5.1 DESCRIPTIONTaking the previous analysis from this chapter into account, the settings have been calculated as shown in below.Table 9–9: NORTH BUS DIFFERENTIAL PROTECTION SETTINGSSETTING VALUE COMMENTSPICKUP 0.1 pu Default value. Lower or higher values may be entered upon security/dependabilityrequirements. The pu value is for the base of 1200A. This means the actual pickup is120 A primary.LOW SLOPE 25% Default value. Lower or higher values may be entered upon security/dependabilityrequirements.LOW BPNT 1.79 pu None of the CTs will saturate for ac currents below 1.79 pu even with 80% remanence.The dc component, however, combined with the remanence may saturate some CTseven for currents below 1.79 pu. The B30 copes with saturation using the currentdirectional principle.HIGH SLOPE 60% Default value. Lower or higher values may be entered upon security/dependabilityrequirements. The value of 60% ensures that the differential characteristic alone(without the directional principle) will work correctly under ac saturation of the CTs(26% of spurious differential during the fault on C-1 saturating CT-1).HIGH BPNT 8.96 None of the CTs will saturate for ac currents below 8.96 pu. The dc component,however, may saturate some CTs even for currents below 8.96 pu. The B30 copes withsaturation using the current directional principle.HIGH SET 5.94 The maximum spurious differential current is 2.97 pu. Due to limited accuracy ofanalysis and the effect of dc saturation a security factor of 2 has been adopted. Thehighest internal fault current is 14kA, or 11.67 pu giving a good chance to clear anumber of faults by the unbiased differential operation.Table 9–10: SOUTH BUS DIFFERENTIAL PROTECTION SETTINGSSETTING VALUE COMMENTSPICKUP 0.1 pu Default value. Lower or higher values may be entered upon security/dependabilityrequirements. The pu value is for the base of 1200A. This means the actual pickup is120 A primary.LOW SLOPE 25% Default value. Lower or higher values may be entered upon security/dependabilityrequirements.LOW BPNT 1.83 pu None of the CTs will saturate for ac currents below 1.83 pu even with 80% remanence.The dc component, however, combined with the remanence may saturate some CTseven for currents below 1.83 pu. The B30 copes with saturation using the currentdirectional principle.HIGH SLOPE 60% Default value. Lower or higher values may be entered upon security/dependabilityrequirements. The value of 60% ensures that the differential characteristic alone(without the directional principle) will work correctly under ac saturation of the CTs(24% of spurious differential during the fault on C-2 saturating CT-2).HIGH BPNT 9.13 pu None of the CTs will saturate for ac currents below 9.13 pu. The dc component,however, may saturate some CTs even for currents below 9.13 pu. The B30 copes withsaturation using the current directional principle.HIGH SET 5.54 The maximum spurious differential current is 2.77 pu. Due to limited accuracy ofanalysis and the effect of dc saturation a security factor of 2 has been adopted. Thehighest internal fault current is 14kA, or 11.67 pu giving a good chance to clear anumber of faults by the unbiased differential operation.
