Star-Star Differential Protection
Star-Star Differential Protection
(OP)
15 MVA 33/11 kV YNyn0 (solidly grounded) transformer to be protected. I propose the following:
1- REF HV
2- REF LV
3- HV OC/EF
4- LV OV/EF
5- Buchholz
6- Pressure Relief.
I think these are enough, nevertheless, I wonder if I need a full differential protection on the transformer? I think that restricted earth fault on HV & LV are enough and no need for additional protection.
any clue? anything I missed?
1- REF HV
2- REF LV
3- HV OC/EF
4- LV OV/EF
5- Buchholz
6- Pressure Relief.
I think these are enough, nevertheless, I wonder if I need a full differential protection on the transformer? I think that restricted earth fault on HV & LV are enough and no need for additional protection.
any clue? anything I missed?






RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
I have read that it is common to provide diff. protection for transformers greater than 5 MVA and some say it is crucial at 10+ MVA. Well, but I have seen some applications at 15 MVA without any. As cranky mentioned, it is like insurance.
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
I have read somewhere that it is sometimes advisable to have separate relays for reliability issues. I see no much gain here as at the end you have the same CT so any failure in it will lead to same result with any number of relays!. The only gain will be to avoid issues if the one relay failed...
RE: Star-Star Differential Protection
You may not need it now but also consider adding trip coil monitoring to HV/LV breakers and lockout relay (if used). The SEL and GE relays mentioned previously have sufficient inputs to these and other quantities. If someone wants SCADA in the future, you are ready for it.
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
RE: Star-Star Differential Protection
Today, newer protective terminals is "zero" price.
Put full redundancy scheme with full functionality.
RE: Star-Star Differential Protection
It also depends on the system operating configuration such as down stream and upstream supply system configuration (bus tie-open/close etc.), how important to save the network itself, is it a distribution transformer or a generator transformer. Hence a generic solution may not be appropriate.