Connect two MV switches in series

[aelkhatib]

Can we have design where an MV switch (with feeder fuse 100A) is feeding another MV switch, which is feeding multiple sections of a facility through distribution feeds?
(Pic for reference.)
I was made aware that chaining MV switches in series like this is not a good practice. Can someone explain to me why?

 

[zbang]

Dunno, putting them in series like that seems like good practice- much easier to do maintenance on the downstream switches and bus work.

(Any time someone tells me that what seems sensible is "bad", I gotta ask why; often the reason is nonsense.)

 

[Hv&Lv]

It’s done on utility lines every day. It’s normal practice. Just make sure coordination works.
we have some lines that from station to end, could have 7-8 in- series protections.

 

[paulengr]

That is called metal enclosed gear. It even has its own ratings. It is also often built as MVCCs with class E2 starters or transformer feeders.

You might be thinking of ferroresonance or problems with current forcing to zero which causes switching transients. There are solutions to both even at medium voltage such as “soft” contacts and switching resistors but that’s more of a switch design issue.

 

[Jraef]

Maybe someone is thinking that every switch has resistance, so switches in series is like having resistors in series?

That said, the safety and reliability benefits of sectionalization can far outweigh any minor issue with causing a tiny amount of voltage drop. As said, this is done all the time.