GE P742

P74
x/EN AP/Na7
Application Notes
(AP) 6
-26 MiCOM P74
1, P742, P743
AP
FIGURE 7: PU – 50BF DISABLED
5.2.2 Overhaul
FIGURE 8: PU – OVERHAUL
In this mode the feeder is totally disconnected from the system because all the isolators are
open but all information is passed back to the central unit for inclusion in zone calculations
and hence the protection scheme. Hence the central unit can keep the zone elements in
service as the contribution of this feeder will be zero. (The CT is still used by the Check Zone
element)
Whilst in this mode the peripheral unit can be tested locally for example secondary injections
tests can be carried out.(The system is stable because during the current injection there is a
differential current in the CZ but not in the Zone)
To test other protection
relays such as Distance,
Feeder...
50BF
Feeder In
Service
Primary
current
Central Unit: Normal
Trips
50/51
DZ-
50BF
Currents, Topology
Isolation to
be
P0708ENb
* The status
positions can be
forced closed.
If so a busbar trip
could occur if the CU
is not in maintenance
mode.
Feeder Out of
Service
Both isolators
and CB forced
Open*
No primary
current
50BF
Central Unit: Normal
Currents, Topology
No Trips
To test the PU
50/51
DZ-
50B
P0709ENb