Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Transformer Differential Protection (87) 1
- Thread starter sky2020
- Start date
RRaghunath
Electrical
Transformer differential protection can detect SLG faults.
Only thing is that the zero sequence filtering that is adopted in the protection settings desensitises the protection to some extent (makes it less sensitive in other words) against SLG faults.
Only thing is that the zero sequence filtering that is adopted in the protection settings desensitises the protection to some extent (makes it less sensitive in other words) against SLG faults.
-
1
- #3
davidbeach
Electrical
Need to back up to the "It Depends" stage of answering the question. What's the transformer? What are the "primary" and "secondary" winding configurations? (I like high-side and low-side much better than primary and secondary, they don't change with application.) Where in the winding is the fault?
Assuming that the "secondary" is a solidly grounded wye, most SLG faults will be detected by a phase 87 element. More can be detected by a negative sequence 87 element (called 87Q sometimes). But the closer you get to the neutral the harder it is for a phase 87 to detect. If the transformer is high impedance grounded, or capacitively grounded (aka ungrounded) then a SLG may not be picked up by the 87.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
Assuming that the "secondary" is a solidly grounded wye, most SLG faults will be detected by a phase 87 element. More can be detected by a negative sequence 87 element (called 87Q sometimes). But the closer you get to the neutral the harder it is for a phase 87 to detect. If the transformer is high impedance grounded, or capacitively grounded (aka ungrounded) then a SLG may not be picked up by the 87.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
davidbeach
Electrical
That’s the theory anyway. Just found out the hard way just how susceptible REF can be to CT saturation on external L-L faults with a bit of neutral current. There is certainly a class of fault for which REF is the most definitive protection element, but to date I’ve seen more REF mistrips than correct operations. A bit jaded at the moment. But I must not be the only one, a major relay supplier recently revamped the REF in their advanced transformer relay. Firmware revision time…
I’ll see your silver lining and raise you two black clouds. - Protection Operations
I’ll see your silver lining and raise you two black clouds. - Protection Operations
Palletjack
Electrical
David Beach said:
Maybe a dumb question, but isn’t that what the stabilizing resistor is supposed to stop misoperations due to CT saturation??
davidbeach
Electrical
Low impedance REF, one of many functions of a transformer relay all using the same set of CT inputs. No way to include a resistor.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
I’ll see your silver lining and raise you two black clouds. - Protection Operations
- Status
Similar threads
- Question
- Locked
- Question
- Locked
- Question