Standard Fuse Link Selection

[mbrooke]

Does anyone know how to apply "standard" type fuse links to an overhead distribution system?

https://www.sandc.com/globalassets/sac-electric/documents/sharepoint/documents---all-documents/tcc-number-123-6.pdf?dt=637197562667792661

As its done now type K fuse are applied in series secession as 200K, 140K (recloser coordinated with fuse saving curves) 100K, 65K, 40K, 25K and 15K. 6K for transformers. 8, 12, 20, 30, 50 and 80K links are considered intermediate and thus never used. This achieves 100% selective coordination throughout all branches and their associated spurs.

However, I'm unsure as how or if this pertains to type "S" links.

Do I go 200S, 125S, 80S, 50S, 30S? Or 150S, 100S, 65S, 40S, 25S? Or am I way off?

 

[Hv&Lv]

Where did you read 8, 12, and 20s are never used???

some systems use T fuses, some use standards, some use K with KS intermixed.

there are a LOT of things to take into account when picking a fuse or deciding which type to use on any given system.
there really isn’t one “rule of thumb” fits all answer.

before light table and other programs, we had a book with the TCC printed on onion paper. Overlay, look at separation and choose.

to quote many, “protection isn’t a science, it’s an art”
here is a speed comparison.

 

[mbrooke]

Where did you read 8, 12, and 20s are never used???

Don't see them being used to be honest except for maybe the occasional odd ball bank that needs them.

some systems use T fuses, some use standards, some use K with KS intermixed.

In the old days they even used N links I know T is common too.

there are a LOT of things to take into account when picking a fuse or deciding which type to use on any given system.
there really isn’t one “rule of thumb” fits all answer.

This is where my brains conks out lol.

before light table and other programs, we had a book with the TCC printed on onion paper. Overlay, look at separation and choose.

to quote many, “protection isn’t a science, it’s an art”
here is a speed comparison.
View attachment 2551751

Its more complicated than that. S links start under 200% of the rating, K and T start above it. N is around 200%. Which the above graph does not show except in relation to the N link. This in particular confuses me, especially what effect pre-loading has on each link type.

Worse case is a link loaded to its emergency rating and some guy sticks in a "coordinated link" that is stone cold into a faulted line or cable. Hate to have the TCC of the hot link touch the cold link.

 

[Hv&Lv]

Don't see them being used to be honest except for maybe the occasional odd ball bank that needs them.

based on what?
Experience or here say

 

[mbrooke]

based on what?

Looking at poles and engineering documents. The links I mentioned are intermediate links and have no purpose in branch to branch selective coordination.

 

[mbrooke]

If you were to design a distrbution system from scratch, or for that matter a power company with no set of yet established standards what fuse type would you choose, pick and standardize on?

 

[mbrooke]

based on what?
Experience or here say

I guess I should just pick K links. K links start at 200-220% which fits the 2X pickup rule for max load, and the curve is faster than that of T links. If you ask me a lot of it is arbitrary.

 

[mbrooke]

Alright, some comparison. This is interesting.

Type 200T and 200K links both start at around 480 amps when cold, mostly identical except for the shift towards to bottom.

 

[mbrooke]

Now, here is the interesting part. N links start at 408 amps, less than T or K links -BUT- the lower part of the curve is is nearly identical to the K link closing following it.

 

[mbrooke]

Finally the S link, starts at 366 amps, and is faster than than the 3 other fuses.




My question is, why the different pickup settings? I can understand the speed factor, but why start some links below 200% while others at 250%? Why would this be important?

 

[mbrooke]

Made a discovery- I'm dead serious... A 150 S link is identical to a 140K link. Does that mean some links are 100% identical but just labelled differently?




Now the 140K overlayed:



140T overlay just for comparison.





And, here, is where I'm 150N fuse... identical to 140K and 150S huh?

 

[Hv&Lv]

Which is why different places use different fuses.
we use T

 

[mbrooke]

Which is why different places use different fuses.
we use T

I get that each fuse variety is different in some way- but my question is why? Why would one utility need a link that starts at 180% while another at 250% of the same ampere rating? I can get K vs T in terms of inrush, but why all the other kinds, some which appear to be 100% identical just labelled differently.

Or I'll ask it like this: why did your POCO pick T links over say N links?