ABB RELION REX640 Technical Manual page 586

Section 4
Protection functions
580
Breakable
terminal blocks
P1 S1
P2 S2
A
Test device
TIMER
STOP
GUID-FF20B088-F129-456F-8E82-3DDD6D9A1034 V1 EN
Figure 318: Example of connections to test the line differential protection relay
Secondary current injection
There are two alternative modes to check the operation of a line differential protection
relay. These are not exclusive methods for each other and can be used for various test
on the protection relay.
Normal mode
In normal mode, that is, the mode when the function is on normal operation, the local
end protection relay sends phasors to the remote end protection relay and receives
phasors measured by the remote end protection relay. This mode can be used in testing
the operating level and time of the low and high stages of the local end protection
relay. This is due to a test situation when the remote end does not measure any current
and therefore, all the current fed to the local end current circuit is seen as differential
current at both ends.
Testing of the line differential protection is done with both protection relays separated
geographically from each other. It is important to note that local actions in one
protection relay cause operation also in the remotely located protection relay. When
testing the line differential function, actions have to be done in both protection relays.
Before the test, the trip signal to the circuit breaker shall be blocked, for example by
breaking the trip circuit by opening the terminal block or by using some other suitable
method.
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