Description - GE B90 Instruction Manual

10.5 BUS DIFFERENTIAL SETTINGS
10.5BUS DIFFERENTIAL SETTINGS
Taking the previous analysis from this chapter into account, the settings have been calculated as shown in below.
Table 10–9: NORTH BUS DIFFERENTIAL PROTECTION SETTINGS
SETTING
PICKUP
LOW SLOPE
LOW BPNT
HIGH SLOPE
HIGH BPNT
HIGH SET
Table 10–10: SOUTH BUS DIFFERENTIAL PROTECTION SETTINGS
SETTING
PICKUP
LOW SLOPE
LOW BPNT
HIGH SLOPE
HIGH BPNT
HIGH SET
10
10-10
VALUE COMMENTS
0.1 pu Default value. Lower or higher values may be entered upon security/dependability
requirements. The pu value is for the base of 1200A. This means the actual pickup is
120 A primary.
25% Default value. Lower or higher values may be entered upon security/dependability
requirements.
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 CTs
even for currents below 1.79 pu. The B90 copes with saturation using the current
directional principle.
60% Default value. Lower or higher values may be entered upon security/dependability
requirements. 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).
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 B90 copes with
saturation using the current directional principle.
5.94 The maximum spurious differential current is 2.97 pu. Due to limited accuracy of
analysis and the effect of dc saturation a security factor of 2 has been adopted. The
highest internal fault current is 14kA, or 11.67 pu giving a good chance to clear a
number of faults by the unbiased differential operation.
VALUE COMMENTS
0.1 pu Default value. Lower or higher values may be entered upon security/dependability
requirements. The pu value is for the base of 1200A. This means the actual pickup is
120 A primary.
25% Default value. Lower or higher values may be entered upon security/dependability
requirements.
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 CTs
even for currents below 1.83 pu. The B90 copes with saturation using the current
directional principle.
60% Default value. Lower or higher values may be entered upon security/dependability
requirements. 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).
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 B90 copes with
saturation using the current directional principle.
5.54 The maximum spurious differential current is 2.77 pu. Due to limited accuracy of
analysis and the effect of dc saturation a security factor of 2 has been adopted. The
highest internal fault current is 14kA, or 11.67 pu giving a good chance to clear a
number of faults by the unbiased differential operation.
B90 Low Impedance Bus Differential System
10 APPLICATION OF SETTINGS

10.5.1 DESCRIPTION

GE Multilin