You can’t “join up transformers”, a single-phase transformer is an iron core with two sets of copper or aluminum windings around it. As far as I know, the only way to increase the volt-amp rating is more iron and copper/aluminum. Wiring them in series doesn’t increase the volt-amp rating but you can use (3) paralleled single-phase transformers for a three-phase circuit, I occasionally see a set of three medium-voltage to 480V ‘pineapple’ transformers (with visible live parts!) at the service entrance for older buildings.
I know you can wire transformers in series, but doesn’t that just change the voltage? As far as I understand it, if you have a 75kva 7.2kV -> 480V wired in series with a 75 kva 480V -> 208V transformer, you still only have 75 kva at the secondary of the second transformer.
Could you parallel two (or more) sets of three single-phase transformers into a single circuit on the secondary side assuming they were all identical and the conductors are all the same length? I assume it’s more economical to just have one three-phase transformer for instrumentation/control and switching reasons, just wondering on a theoretical level.
Not an EE, but if transformers are at all like smaller scale power supplies, the issue with using multiple smaller components is it works right up until it doesn't. If you lose one or it gets overloaded, it puts more strain the rest, increasing the failure risk. Then another one pops, and the load shifts to the smaller pool, in a cascade failure.
To an extent, you can do this, as long as you have systems in place to shed load and prevent the components from failing in quick succession by circuit breaking.
Also i believe transformers are much more graceful handling overcurrent than silicon. But everything has its limits.
Since kva literally just means ‘kilovoltamps’ and is calculated by multiplying volts * amps, and transformers convert step up and down voltages while keeping amperage roughly the same (to the first order approximation), then yes. Minus losses.
And yes, you could parallel sets of even series transformers together. It will work fine, until something happens and then it doesn’t (or explodes). Making that not happen is relatively non trivial and is a lot of why keeping a working power grid working is non trivial and a lot of work.
At larger scales, when this goes wrong it can cause grid blackouts. Smaller scales, fires.
Since a single transformer rated for the load it will carry is pretty simple and ‘just works’ in almost all scenarios, it’s more economical just using a single one when you can.
No sane way to do that with two different power plants on opposite sides of the state, of course.
Why can’t we mass manufacture aircraft carriers by making a lot of small boats and joining them up?
It’s the same kind of problem.
(And notably, it’s not that it’s actually completely impossible to do it that way - just impractical compared to the alternative. You could actually make something that kind of sorta worked for an aircraft carrier by joining tens of thousands of small pontoons and support ships. Operationally, it would just suck compared to the alternative.)
> You could actually make something that kind of sorta worked for an aircraft carrier by joining tens of thousands of small pontoons and support ships.
In fiction: "Tom Swift and his Ocean Airport" (1934) [1]
In reality, a floating pontoon airport, with over 10,000 pontoons, was built during WWII, as "Project Sock".[2] It worked OK in a protected bay. Once large planes could cross the Atlantic, and small carriers with small planes were built for convoy protection, there was no military need. Floating airports have been tried a few times since, but it's never been worth the trouble.
Prefabricated pontoons were a big thing in WWII. Used for bridges, barges, docks, etc.
Useful when you really need a temporary structure in a hurry, and aren't too concerned about
its long term lifespan.
Putting multiple transformers in series is quite possible, but
it's rarely done because it's less efficient than a larger transformer and takes up more space.
Dumb question: why can’t we mass manufacture smaller transformers and join them up?