ABB 615 series Technical Manual page 494

Section 4
Protection functions
488
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.
When injecting current to one phase in the local end protection relay, the current is seen
as a differential current at both ends. If a current I
differential and stabilizing currents for phase A are:
ID A I _
=
injected
GUID-B5B84B9B-B26C-421F-B4D0-E301EE4883F3 V3 EN
IB A I _ / 2
=
injected
GUID-6A1A367B-241B-4831-A1F2-9373AE4D26ED V1 EN
The operation is equal for phases B and C.
Verifying the settings
1. Block the unwanted trip signals from the protection relay units involved.
2. Inject a current in phase A and increase the current until the function operates for
phase A.
The injected operate current corresponds to the set Low operate value. The
monitored values for ID_A should be equal to the injected current.
3. Repeat point 2 by current injection in phases B and C.
4. Measure the operating time by injecting the single-phase current in phase A.
The injected current should be four times the operating current. The time
measurement is stopped by the trip output from the protection relay unit.
5. Disconnect the test equipment and reconnect the current transformers and all other
circuits including the trip circuit.
Phasor echoing method
The line differential function in one protection relay can be set to special test mode, that
is, the Operation setting is set to "test/blocked". When this mode is in use, the remote end
protection relay echoes locally injected current phasors back with the shifted phase and
settable amplitude. Therefore, the local end line differential function is also automatically
blocked and the remote end line differential function discards the phasors it receives from
the protection relay in the test mode.
When the test mode is active, the CT connection type is still used by the line differential
protection function as in the normal operation mode. The setting can be used for shifting
the phase (0 or 180 degrees).
1MAC059074-MB A
is injected, A in phase A, the
injected
Technical Manual
(Equation 78)
(Equation 79)
615 series ANSI