Distributed Bus Protection - GE L90 Instruction Manual

9 APPLICATION OF SETTINGS 9.2 CURRENT DIFFERENTIAL (87L) SETTINGS

9.2.8 DISTRIBUTED BUS PROTECTION

In some cases, buses of the same substation are located quite far from each other or even separated by the line. In these
cases, it is challenging to apply conventional bus protection because of the CT cable length. In other cases, there are no
CTs available on the line side of the line to be protected. Taking full advantage of L90 capability to support up to 4 directly-
connected CTs, the relay can be applied to protect both line and buses as shown below. Proper CT/VT modules must be
ordered for such applications. The varying CT ratios at the breakers can be compensated locally by using the sources
mechanism and with the settings between remote relays. If more than 4 but less than 8 CTs are to be connected to
CT TAP
the L90 at one bus, the 3-terminal system can be applied, provided the user does not exceed a total of 12 CTs.
Figure 9–2: DISTRIBUTED BUS PROTECTION
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GE Multilin L90 Line Differential Relay 9-7