Connect two MV switches in series

aelkhatib

Member
Location
Minneapolis
Occupation
Electrical Designer
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?

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Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
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

Senior Member
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

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
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.
 
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