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1MRK 504 165-UEN Rev. K
3.
Check that the trip and alarm contacts operate according to the configuration logic.
4.
Decrease the current slowly from operate value and note the reset value.
5.
Repeat the procedure by injecting current in phases L2 and L3 respectively.
11.3.5.8
Verifying the operate characteristic
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.
Transformer protection RET670
Commissioning manual
IEC18000248 V1 EN-US
Figure 24:
Single-phase pickup factor when ZSCurrSubtrW2 = On
For phase angle shifts greater than ±30 degrees, actual operation will happen in
one of the other two phases where the current has not been injected.
The pickup current is dependent on the actual phase angle shift across the
protected PST.
© 2017 - 2022 Hitachi Energy. All rights reserved
Section 11
Testing functionality by secondary injection
GUID-2A65B94E-3525-4022-A237-B8ABC596DC92 v2
101
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