GE Industrial Solutions Entellisys System User Manual - Manual (Page 99)

PT Throw-Over 99
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7.3 PT Throw-Over
The PT Throw-Over changes the voltage source for the metering and relay functions for a circuit
breaker, based on how a bus is powered. It is recommended that you review the chapter on
Zones and Topologies (see
Zones, buses, and topologies on page 85 ) before continuing, since
many of the terms and concepts used here are defined more thoroughly in that chapter.
Consider the main-tie-main system shown in Figure 7-8. Typically there is a power source, such
as a utility source or generator, connected to each main (circuit breakers M1 and M2) and a set
of potential transformers (PTs) at each main that step down the primary voltage so that it can
be measured by the EntelliGuard Messenger at the circuit breaker.
Figure 7-8 One-line diagram for a main-tie-main
One of the advantages of Entellisys is that voltage information measured at one circuit breaker
can be used for metering and relaying functions at another circuit breaker. In the system shown
in Figure 7-8, what voltage information should be used for the feeder circuit breakers (FL1, FL2,
FR1, and FR2)?
The answer, of course, depends on the state of the topology circuit breakers M1, M2, and T1 (see
Zones, buses, and topologies on page 85 for more information). For example, if the source at
circuit breaker M1 is powering Bus 1 (i.e., M1 is closed, T1 is open) then the metering and
relaying functions at FL1 and FL2 should use the voltage data from M1. If M2 is powering Bus 1,
then the metering and relaying functions at FL1 and FL2 should use the voltage data from M2.
NOTE: Although the main-tie-main is a common configuration, this feature is not limited to
that configuration.