Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-2 973.334.3100
13.1.1.1 BACKUP PROTECTION
The protection algorithms just described are the “primary” protection routines and are intended to
provide protection with relays at both ends of the line being protected and a communications link
between the relays. There will be unavoidable failures in the communications link and the relay
provides some backup protection algorithms to maintain protection even without a functioning
communications channel.
Overcurrent
Time Overcurrent
Close Into Fault
Loss of Load
The relay also has a stub bus protection feature. When an 89 disconnect is used to disconnect a line
from the remote end it may leave a bus stub energized and requiring protection. The 89B contact can
be fed into the relay to enable the stub bus feature.
The stub bus function basically isolates the local and remote relays. The local relay will operate using
only overcurrent and time overcurrent routines that are similar to the backup routines but have
independently programmable settings. The remote relay will then continue to operate in primary
protection mode but will be told that the local (stub-bus side) relay is receiving zero current through
the line.
13.1.2 ADDITIONAL FUNCTIONS
The current differential relay also provides several additional functions:
Direct Transfer Trip (DTT)
Transferred Status Bits
Sequence of Events
Oscillography
Recloser Block
Local Charge Comparison Trip Alarm (LCCT)
13.2 CONFIGURATION
13.2.1 SYSTEM CONFIGURATION OVERVIEW
The GARD 8000 System differs from most conventional multifunctional differential relays in that
rather than supplied with very complex generic default logic, the GARD 8000 can be easily
customized to meet your specific application requirements.
For most applications, the factory default logic may be suitable but RFL will modify it free-of-charge
when required.
The advantage with custom logic is that the user interface is greatly simplified as the web pages for
logic settings are automatically created to correspond to the actual logic.
While the logic is custom made, a considerable amount of settings and field flexibility can be built-in
to cover a large number of application needs. For instance, mapping of inputs and outputs, inverters for
inputs and outputs, timers, communications channel selections, etc. can all be made on web pages as
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