GE b30, Инструкция по эксплуатации

Страница: 539 / 632

CHAPTER 8: APPLICATION OF SETTINGS BUS DIFFERENTIAL SETTINGS
B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 8-11
8
Table 8-8: External fault calculations on C-5
8.5 Bus differential settings
8.5.1 Description
Taking the previous analysis from this chapter into account, the settings have been calculated as follows.
Table 8-9: North bus differential protection settings
Table 8-10: South bus differential protection settings
CT I
FAULT
(kA) I
FAULT
(A sec) T
DC
(ms) AC saturation DC saturation t
SAT
(ms)
CT-1 0 0.00 N/A No No N/A
CT-2 0 0.00 N/A No No N/A
CT-3 6.0 25.00 5 No No N/A
CT-4 5.0 25.00 30 No Yes 26.37
CT-5 11.0 55.00 30 No Yes 9.45
CT-7, CT-8 11.0 45.83 30 No Yes 11.54
Setting Value Comments
PICKUP 0.1 pu Default value. Lower or higher values can be entered upon security/dependability
requirements. The pu value is for the base of 1200A. This means the actual pickup is 120 A
primary.
LOW SLOPE 25% Default value. Lower or higher values can be entered upon security/dependability
requirements.
LOW BPNT 1.79 pu None of the CTs saturate for AC currents below 1.79 pu even with 80% remanence. The DC
component, however, combined with the remanence can saturate some CTs even for currents
below 1.79 pu. The B30 copes with saturation using the current directional principle.
HIGH SLOPE 60% Default value. Lower or higher values can be entered upon security/dependability
requirements. The value of 60% ensures that the differential characteristic alone (without the
directional principle) 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 saturate for AC currents below 8.96 pu. The DC component, however, can
saturate some CTs even for currents below 8.96 pu. The B30 copes with saturation using the
current directional principle.
HIGH SET 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.
Setting Value Comments
PICKUP 0.1 pu Default value. Lower or higher values can be entered upon security/dependability
requirements. The pu value is for the base of 1200A. This means the actual pickup is 120 A
primary.
LOW SLOPE 25% Default value. Lower or higher values can be entered upon security/dependability
requirements.
LOW BPNT 1.83 pu None of the CTs saturate for AC currents below 1.83 pu even with 80% remanence. The DC
component, however, combined with the remanence can saturate some CTs even for
currents below 1.83 pu. The B30 copes with saturation using the current directional principle.
HIGH SLOPE 60% Default value. Lower or higher values can be entered upon security/dependability
requirements. The value of 60% ensures that the differential characteristic alone (without the
directional principle) 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 saturate for AC currents below 9.13 pu. The DC component, however, can
saturate some CTs even for currents below 9.13 pu. The B30 copes with saturation using the
current directional principle.