What is a solid insulation switchgear (SIS)? Benefits of SIS vs AIS/GIS.

You all know what an indoor air insulted metal cald switchgear is?

It has bus bar vacuum circuit breaker, CT, PT, relays, meters, switches for breaker operation, indication bulbs and cable compartment.

Solid insulation switchgear also has all of this. There is no change.

So, what is the change ?

As the name suggests, it has solid insulation instead of air insulated.

But what is the solid insulation and where it is?

Solid insulation means epoxy insulation.

And where, all the bus bar, CT, PT, cable termination are enclosed in epoxy insulation.

So, why we want to enclose the bus bar in the epoxy insulation…

Answer is very simple .

When the bus bar is separated(enclosed/insulated) by epoxy than less space is required for housing of the bus bar so panel dimensions reduced, that is overall goal of SIS switchgear.

just like, we save space in case of GIS switchgear, in-comparison to AIS switchgear.

See below cross-section diagram of a SIS panel.

Credit: Schneider Electric

Now what we find in the above picture, bus bar is enclosed in epoxy, breaker and isolator is in epoxy and cable terminals are in epoxy. it means, entire main circuit is in epoxy i.e. solid insulation

Can you answer why this is called Solid insulation switchgear, not by any other names…

Because we have already two switchgears i.e. Gas insulated switchgear and Air insulated Switchgear (Air is just a mixture of atmospheric gases) and in old days, oil type switchgear had been used.

So, to distinguish and more appealing, it is termed as solid insulation switchgear. Aso, not only epoxy is used, but also EPDM is also being used as insulation in solid state switchgear

Benefis of Solid insulation switchgear :

a) Panel dimensions are drastically reduced. so, the floor area required will be less.

b) Since SF6 gas is not used so it is environmentally friendly.