Transformer Primary Protection vs. Tap Line Protection 2

[tmaly1]

Dear Folks,

I went over Bussmann's SPD Book and Cooper's Electric Distribution Protection Handbook, they all seem to explain how to protect individual TX primary. I would like to know how to incorporate that with Tap Line fuses (in case having more than one TX's down the tap line). Do you install one fuse at the 1st TX and size it such that it protects all TXs down the line from that point or do you still have to protect each individual TX with a separate fuse?

Thanks in advance for your feedback and insight

 

[tinfoil]

Normally, each transformer is separately fused, with an appropriate size to protect the transformer (based on its damage curve), yet large enough to not blow during transformer energization (inrush effects plus connected "cold-load").

The tap fuse must be 'bigger' (i.e. slower) than the largest transformer fuse, yet small enough to coordinate with the upstream protection, such as the substation relaying.

Fuse manufacturers such as S&C or Cooper have downloadable guidelines on their sites that are pretty good tutorials on fuse-fuse and fuse-relay coordination.

 

[rconnett]

tmaly - the answer varies dramatically depending upon your application. If this is a 480 volt system with small dry type transformers, the NEC or similar standard will apply (whatever is used in your country).

If this is an overhead medium voltage (e.g 13kV) distribution system with small transformers - 50 kvA, etc, tinfoli's approach is correct.

If this is a large transmission line application, (e.g 69 kV + with larger substation style transformers - it is a differnt question, and the transformers may warrant more sophisticated protection.

I suggest the IEEE Buff Book or the IEEE Red Book (ANSI/IEEE 141-xxx) may be helpful under 'transformer protection'

 

[tmaly1]

Thank you folks, I appreciate your feedback and comments, they are very helpful for me.