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 IED, 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:
GUID-B5B84B9B-B26C-421F-B4D0-E301EE4883F3 V3 EN (Equation 41)
GUID-6A1A367B-241B-4831-A1F2-9373AE4D26ED V1 EN (Equation 42)
The operation is equal for phases L2 and L3.
Verifying the settings
1. Block the unwanted trip signals from the IED 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 IED 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 IED 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
IED 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 IED 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).
Section 4 1YHT530004D05 D
Protection functions
372 615 series
Technical Manual
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