Difference between Connection code 9 and 20 (Zero Sequence)
Using ODMS10 model to extract a PSSe v32 file (Raw and seq), however when I open it in PSSe 34 Some Ynyn0 transformers extract as Connection code (CC) 9, but the program suggests it should be (in the vector group) CC 20. What is the zero sequence difference between these two CCs, as it isn't discussed in the PSSe manual.
I tried testing the same transformer in a basic Gen + Transformer + Load model. When I fault the LV bus it get a different earth fault for the two CCs. (results below
- Connection Code 9
X------------ BUS ------------X PU PU 40085 [XXXXX 33.000] 3PH 0.99 0.0781 -0.9906 LG 1.10 -0.1287 -1.0884 THEVENIN IMPEDANCE, X/R (PU) Z+:0.806215+j0.634362, 0.78684 Z-:0.806215+j0.634362, 0.78684 Z0:0.201859+j0.851560, 4.21859
- Connection Code 20
X------------ BUS ------------X PU PU 40085 [XXXXX 33.000] 3PH 0.99 0.0781 -0.9906 LG 1.41 0.0242 -1.4112 THEVENIN IMPEDANCE, X/R (PU) Z+:0.806215+j0.634362, 0.78684 Z-:0.806215+j0.634362, 0.78684 Z0:0.004812+j0.173282, 36.01337
The short circuit CC drop down menu identifies 9 as "Series path on each side, ground path at junction (auto) and 20 as "Series path on each side, ground path at junction".
Now I understand that from v33 onwards the zero sequence model for the CCs was expanded and I'm wondering if this is why the earth fault and zero sequence Thevenin equivalent model so different?
Regards,
Andrew
