Why dont use the restricted earth fault protection for autotransfo?

[ngminhtrung]

Hi everyone, I'm reading the technical manual of numerical relay (SIPROTECT 7UT6), and they say that" Note that the restricted earth fault protection (cannot be applied for busbars or auto-transformers". Someone could tell me the reason?

 

[slavag]

Hi.
It seems strange. Maybe it say about LI REF, in this case possible that this relay isn't included LI REF for the AT, only for trafos. For AT's LI REF need function included
currents from HV side, LV side and neutral point.
But, I sure possible option for the HI REF function into this relay.
We'll wait response from guys, who know this relay.
Regards.
Slava

 

[ngminhtrung]

Thank Slavag for ur consideration, but now I understand,it's fault of 7UT6 relay technical manual. In manual of version 4.0, they wrote like above " Note that the restricted earth fault protection (cannot be applied for busbars or auto-transformers". Then in version 4.6, they correted it, just "cannot be applied for busbars". I dont know why they were so careless. Problem solved

 

[ngapeisue]

Hi all,
To Trung – in the past I had got the question like you. In fact, restricted earth fault function is also available in all kinds of 7UT6x relays. Then you can set the function provided that the CTs at HV, LV sides and neutral point of trans. is available.
The reason why the SIPROTECT 7UT6 manual document wrote "Note that the restricted earth fault protection cannot be applied for auto-transformers" is that for auto-transformers, Siemens provides a standard protection scheme using 7VH600 as a 50 REF (or 87TE or Restricted Earth Fault) so that the similar function in 7UT6x is not be used any more. In practice, if a separated relay like 7VH600 is not used then 50REF in 7UT613 should be set.
I hope that the answer is useful for you. Anybody has an idea, pls share with us!

Regards,