Relay Function 87 for Transformer Protection

Merry Christmas

faresos

Senior Member
Hello Everyone,

I have a situation where we have 3750KVA transformer with 12.47KV Pri-4.16KV Sec. The primary side is protected by feeder with SEL 751 Relay using 51P function (the 50 function is disabled to provide better coordination) and SEL 51G (Residual ground fault protection). SEL 587 relay will be used to protect the transformer against internal faults between the primary and secondary side. My question is, since the 87 function only used to protect against internal faults only of the transformer, is there any coordination setting is required between the 51 function and 87?
 

faresos

Senior Member
51 is overload protection and needs to coordinate with all the downstream stuff on the secondary. 87 doesn't need to coordinate with anything. You definitely want 87 to go first.
That's what I thought but it's nice to know if someone has different opinion. Thanks Joe!
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
My question is, since the 87 function only used to protect against internal faults only of the transformer, is there any coordination setting is required between the 51 function and 87?
No. The 87 element when properly applied discriminates between internal and external faults. No need to coordinate this with other devices as it is supposed to operate with no intentional delay.
 
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