Completing The Test; Self-Adaptive Differential Protection For Two-Winding Power Transformers Pstpdif (87T); Preparing The Function For Testing - ABB Relion 670 Series Commissioning Manual

1MRK 504 165-UUS Rev. J
5. Connect a trip output contact to a timer.
6. Decrease the injected current stepwise to 50 % of the trip level and check the time delay.
7. Repeat steps 3 – 6 for phases B and C.
11.3.4.2

Completing the test

Continue to test another function or end the test by changing the test mode setting to disabled. Restore
connections and settings to their original values, if they were changed for testing purposes.
11.3.5 Self-adaptive differential protection for two-winding power
transformers PSTPDIF (87T)
11.3.5.1

Preparing the function for testing

Prepare the IED in general for verification of settings outlined in Section
settings.
Navigate to Main menu/Test/Function test mode and make sure that only the PSTPDIF function and
associated trip function blocks are enabled. All other protection functions, which may interfere with
testing or tripping shall have the setting Blocked set to Yes.
The PSTPDIF function is self-adaptive. Thus, special measures and procedures shall be used during
testing. Off-the-shelf available test sets with associated software and their testing routines for standard
transformer differential protection will not work, in general, for this function. They may work for special
case, when the phase angle shift is zero degree (i.e. as for Yy0 standard power transformer). However,
for specific phase angle shift (e.g. tap position) of the protected PST, which is different from zero degree,
this standard routines cannot be used.
To test this function, it is strongly recommended to use a test set with six current sources and then follow
the sequence-wise testing procedure as explained for the traditional transformer differential protection in
the paper Easy and Intuitive Method for Testing Transformer Differential Relays published by Hitachi
Power grids. This paper is available on the Hitachi Power grids website.
To prepare the function to be tested for specific phase angle shift (e.g. specific tap position) of the
protected PST, proceed as follows:
1. Make sure that the binary input STOPCOMP into PSTPDIF function has the logical value zero.
2. Wait for five seconds and inject the rated load using the positive sequence current systems only on
both sides of the PST, which correspond to the set default transformation ratio and phase angle
shift (typically, zero degree). Instructions on magnitude calculation and phase angles for the six
currents to be injected are available in the above mentioned paper. When currents are injected
correctly, check that all three differential currents are approximately 0% and the bias current is
100%. These values are available as outputs and service values from the PSTPDIF function.
3. Slowly (for example, one degree per second) rotate the positive sequence currents (i.e. all three
phases together) for winding two side until the required phase angle shift is achieved. Note that the
rotation in anti-clock-wise direction of winding two positive sequence current will result in
corresponding but negative value of the estimated phase angle shift displayed on the IED. When
PST is of an asymmetrical design, the magnitudes of the currents on the winding two side shall
also be adjusted accordingly. Once the desired tap is reached, make sure that all three differential
currents are still approximately 0% and the bias current is still 100%. Also, check that DIFRATIO
Transformer protection RET670
Commissioning manual
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Section 11
Testing functionality by secondary injection
GUID-BE74F565-7465-4300-B2A6-D99CE8844147 v2
GUID-8C8A342F-0819-4C6E-A32F-E01DB398B8ED v1
GUID-E2D0D0CB-FA4D-4ED0-9BBB-2D1440804F83 v2
Preparing the IED to verify
101