ABB RELION REX640, Техническое руководство, Страница: 669 / 1960

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.
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
injected
is injected, L1 in
phase L1, the differential and stabilizing currents for phase L1 are:
ID A I
injected
_
=
(Equation 154)
IB A
I
injected
_
=
2
(Equation 155)
The operation is equal for phases L2 and L3.
Verifying the settings
1. Block the unwanted trip signals from the protection relay units involved.
2. Inject a current in phase L1 and increase the current until the function operates
for phase L1.
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 L2 and L3.
4. Measure the operating time by injecting the single-phase current in phase L1.
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.
1MRS759142 F Protection functions
REX640
Technical Manual
669