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This is the so called vector group matching for the per-unitized currents of the transformer. This
matching is necessary when either of the transformer side is connected to delta but another is
connected to star. In non numeric relays this matching was done with interposing CTs which were
connected in the power transformer star side to delta and delta side to star to get the HV and LV side
vectors matching each other. When these got currents were summed in the relay inputs HV and LV
side currents negate each other when there is no difference thus not causing trip. If the currents would
have difference then current should flow to relay input and if there is enough difference it would cause
pick-up and trip. This is not the case with modern differential relay, which does this transformation by
calculating internally the corrected vectors.
Figure. 5.4.10. - 100. Expected phase shifts from HV side to LV side in symmetrical situation.
Now the direction of the CTs starpoint on the HV side and LV side has effect on how to set the
differential calculation method. It is possible to set either “add” or to “subtract” which means that the
CTs “current direction” has to be taken into account. Now in this example the correct setting would be
“add” since the CTs in the main circuit are connected to opposite each other “the starpoints /
groundings are “opposite” thus the measured currents from the CTs are opposite to each other. Now
this is again up to the user which way the signals are wanted to be shown, it is possible also to negate
the CTs currents when the “subtract” mode can be used for differential calculation and the both sides
measurements could be shown as one star connected vector diagram.
As mentioned now the differential algorithm itself, it has calculating formula per each phase difference:
Subtracting formula:
Or Additive formula:
Can be selected based into the CTs connections.
AQ-T216
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
128
Содержание AQ 200 Series
Страница 1: ...AQ T216 Transformer protection IED Instruction manual ...
Страница 243: ...Figure 7 1 162 AQ T216 variant with binary input modules AQ T216 Instruction manual Version 2 00 Arcteq Relays Ltd 242 ...
Страница 264: ...Figure 8 11 184 Panel cut out and spacing of the IED AQ T216 Instruction manual Version 2 00 263 Arcteq Relays Ltd ...
Страница 284: ...10 Ordering information AQ T216 Instruction manual Version 2 00 283 Arcteq Relays Ltd ...
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