RFL Electronics RFL 9300 - Figure 3-20. Zero-Sequence Current Flows through Transformer; Figure 3-21. Typical Tapped Line Application

Figure 3-20. Zero-sequence current flows through transformer
3.14.1 CALCULATIONS FOR LOW-SIDE FAULTS
Figure 3-21 shows a typical tapped line application. Assume that the high-side three-phase fault current under
minimum system conditions is 15,000 amperes primary (which is equal to 31.25 amperes secondary). To con-
duct a worst-case analysis of this application, a maximum system will be considered (all generators and all lines
in service). The equivalent system impedance will be ignored, so the high-voltage bus at the tap will be treated
as an "infinite" source. It is also assumed that all the limiting impedance for the low-side fault is due to the trans-
former impedance. This will introduce a safety factor of about 10-percent into the calculations.
Figure 3-21. Typical tapped line application
RFL 9300 RFL Electronics Inc.
August 25, 2000 3 - 22 (973) 334-3100