Differential Protection

[EECR7]

There is a 10KVA, 23KV - 4.16KV, PAD MTD Transformer. My question is, Does this transformer need differential protection? And is it common to see transformers of this size to have differential protection?

 

[jraef]

10kVA???? Are you sure that wasn't 10MVA?

As a general rule, I have only seen differential protection used at 2500kVA (2.5MVA) and above. So if it is 10MVA, sure. 10kVA, no.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

Never seen it on a 10 KVA nor on a 100 KV.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

You mean neither 10 kVA nor 100 kVA?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[EECR7]

My bad. I meant 10MVA. Thanks for the feedback!

 

[RRaghunath]

Some utilities specify differential protection for transformers rated 5MVA and above.

 

[JG2828]

IEEE C37.91-2000
"6.2 Differential protection
Current differential relaying is the most commonly used type of protection for transformers of approximately 10 MVA three-phase (self-cooled rating) and above."

 

[cranky108]

I believe the type of protection depends on the need you have.

At the time of a fault internal to the transformer, what is the need? It's failed already.
Do you need to disconnect it to reduce the impact? To customers, other equipment, or because it is typical.
What if the fault is on the transformer bushing? Do you have the same needs?

If you truly want to protect a transformer, you need to keep the oil clean, and reduce the number of through faults, and reduce the through fault magnitudes, and reduce clearing times.

So if the goal is to remove the transformer after it has failed, then you only need fuses.