RFL 9300 RFL Electronics Inc.
October 29, 2001 2 - 22 (973) 334-3100
2.7.7 STUB-BUS OPERATION
The transmission line between the local and remote stations may be disconnected via an open line switch at the
local station. If a strong fault occurs at the local station (on the stub or within the double-breaker set-up for ex-
ample) the local station may calculate a trip, and transmit a trip signal to the remote station. Since there is no
fault at the remote station, the remote breaker should not be tripped. To prevent this type of trip, a simple “Stub-
Bus” algorithm will be used:
The relay will require a disconnect switch signal (89B) to make the stub bus function active at the local station,
protecting the stub. When the open disconnect switch is detected, the local station relay will react as follows:
1. A steady stream of WCMs will be transmitted to the remote station(s). All other control signal messages will
be disabled.
2. All trip and control signal messages received at the local station will be discarded. This will effectively dis-
able permissive trip at the local station. The remote station(s) will continue to function in a normal manner.
Permissive trip will still be enabled due to the received WCM signals.
3. The local station relay will be forced into backup mode. This will enable the instantaneous overcurrent func-
tion. Inverse time overcurrent will still be available if the operator chooses to enable the function. The
switch-into-fault and loss-of-load functions will be disabled when stub bus is active.
4. The DTT signal will remain active between stations.
Stations that do not have an active stub bus signal will operate in a normal manner. Standard fault detector re-
quirements must be met in order to trip.
When stub bus is active, backup functions ENABLED or DISABLED will no longer appear on either the pro-
gramming or read menus. Instead “SBACTIVE” will appear on the display in place of ENABLED or DISABLED.
This will inform the operator that stub bus is active and the relay has been forced into backup mode (See Figure
2-9).
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