11.3.5.8 Verifying the operate characteristic
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1. Connect the test set for injection of two three-phase current sets to the current terminals of the IED,
which are connected to the CTs on the winding one and winding two sides respectively of the
power transformer.
2. Inject the x-times (where, x = any value between 1.25*IdMin and 0.95*IdUnre parameters) the rated
load current using the positive sequence current systems only on both sides of the PST.
For actual secondary current magnitudes of the rated PST load, see tests for zero-sequence
current reduction given above. For more details on how to calculate magnitudes and the phase
angles for the six currents to be injected, refer to the paper Easy and Intuitive Method for Testing
Transformer Differential Relays published by Hitachi Power grids. When correct currents are
injected, check that all three differential currents are approximately 0% and the bias current is equal
to x*100%. These values are available as outputs and service values from the PSTPDIF function.
At this point, a stable condition for bias current of x*100% is being injected.
3. If the factor x has a value greater than 5, make sure that the testing is done relatively quickly to
avoid overheating of the input current transformers inside IED. Their continuous rating is 4 times
the rated current (i.e. 1 A or 5 A secondary).
4. Slowly decrease the positive sequence currents (i.e. all three phases together) for winding two side
until the PSTPDIF function gives a trip signal. At that moment, pause the injection and note down
the values of all three differential currents in percent. The bias current still should have the same
value (i.e. x*100%). Similarly, note the secondary current magnitude for winding one and two sides
injected at that point of time.
5. Stop the injection and repeat above points 1-4 for different x-values.
6. From the recorded differential and bias values in percent, draw the operating characteristic from the
measurements. Compare the values as described in the Technical Manual.
11.3.5.9 Completing the test
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Continue to test another function or end the test by navigating to Main menu/Test/IED test mode/
TESTMODE:1 and change the IEDTestMode setting to Off. Restore connections and settings to their
original values, if they were changed for testing purposes.
11.4 Impedance protection
SEMOD53525-1 v2
11.4.1 Distance protection zones, quadrilateral characteristic ZMQPDIS
(21)
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Prepare the IED for verification of settings outlined in Section
"Preparing the IED to verify settings".
Measure operating characteristics during constant current conditions. Keep the measured current as
close as possible to its rated value or lower. But make sure it is higher than the set minimum operating
current.
Ensure that the maximum continuous current to the IED does not exceed four times its rated value, if the
measurement of the operating characteristics runs under constant voltage conditions.
The test procedure has to take into consideration that the shaped load encroachment characteristic is
active. It is therefore necessary to check the setting. To verify the settings with the shaped load
encroachment characteristic the test should be carried out according to figures
25 and 26 and tables 20
and 21. In cases where the load encroachment characteristic is activated tests according to the adjusted
figures should be carried out.
Section 11 1MRK 504 165-UUS Rev. J
Testing functionality by secondary injection
106 Transformer protection RET670
Commissioning manual
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