GUID-FB4ECBAC-1408-4EE6-9F8E-F8F903C84A90 V1 EN
Figure 443: Broken secondary detection by MCS-A, MCS-B, MCS-C
In the example, the incoming feeder is carrying a load of 2.0 pu and both outgoing feeders
carry an equal load of 1.0 pu However, both 87A, 87B, 87C and MCS-A, MCS-B, MCS-
C consider the current as an increased differential or unbalance current because of the
broken CT wire in phase C. Both 87A, 87B, 87C and MCS-A, MCS-B, MCS-C receive
the differential current of approximately 1.0 pu The main differential protection 87A,
87B, 87C cannot trip because of the higher current setting.
All CTs must have the same ratio.
1MAC059074-MB A Section 6
Supervision functions
615 series ANSI 857
Technical Manual
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