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Siemens 7PA30, three phase and single phase trip circuit supervision. Go to: 7PA30

If i got this clear. Ground fault on one phase couses overvoltages in other two phases and in isolated star point. So I need higher insulation level on TR and on switchgear?

Our contractor wants to install power transformer 110/20/6kV, Y,yn9,d11 in a substation. Primary (110kV) wounding of TR is not grounded. 110kV network is directly grounded. Whats are the consequncies of connecting ungrouded primary in grounded network?

So, what is criterion for use of surge arresters? When they are needed? Do I have to place them every time when feeding motor/dry type transformer?

After reading this thread thread240-191665 and this article: http://www.netaworld.org/files/ItemFileA877.pdf, I need to ask one question to get clear something to myself. Article mentioned above, recomends grounding of CT's in protective relay house. I also found same recomendation in some...