Change the magnitude and angle of phase-to-phase voltage to achieve impedances at test
points P1, P2, P3 and P4. For each test point, observe that the output signals, PICKUP and
PU_Zx are activated (where x is 2 or 3 depending on selected zone). After the trip time
delay of the respective zone has elapsed, also the signals TRIP and TRZx (where x is 2 or
3 depending on selected zone) shall be activated.
Load encroachment
Load encroachment operates on the same measuring principles as the impedance
measuring zones. Thus, it is necessary to follow the same principles as for distance
protection when performing the secondary injection tests. Measure operating
characteristics during constant current conditions. Keep the injected current as close as
possible to the rated value of its associated input transformer or lower. Ensure, however,
that it is higher than 30% of the rated current. Ensure that the maximum continuous current
of an IED does not exceed four times Its rated value, if the measurement of the operating
characteristics runs under constant voltage conditions.
Measuring the operate limit of set values of load encroachment function
The load encroachment does not have any special output to be verified. It can only be
verified with the distance PICKUP and TRIP outputs.
Steps to test the load encroachment:
1. Supply the IED with healthy conditions for at least two seconds.
2. Apply the fault condition and slowly decrease the injected impedance to find the trip
value for of the phase-to-ground and phase-to-phase loops.
Under voltage seal-in
The under voltage seal-in logic can be verified using the 27 Trip and 27 PU outputs.
Steps to verify the logic:
1. Keep all the current and voltage in normal balanced condition.
2. Keeping the phase current at rated value, slowly reduce the voltage till it enters into
the respective zone mho characteristics and also below the set value of the under
voltage seal-in logic.
3. Before the trip time delay of the respective zone, reduce the current magnitude so that
the operating impedance moves out of the mho characteristics.
4. The under voltage seal-in should give a PICKUP and TRIP after the trip time delay
is set for the under voltage logic.
11.4.15.2 Completing the test
Continue to test another function or end the testing by setting the parameter TestMode to
Disabled under Main menu/Tests/IED test mode/1: TESTMODE. If another function
Section 11 1MRK 504 165-UUS -
Testing functionality by secondary injection
176 Transformer protection RET670 2.2 ANSI
Commissioning manual
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