Nearly all usecases for a power transformer are now better served by a switched mode power supply.
They tend to be much smaller, lighter, more efficient, cooler and cheaper. They also have features like adjustable output voltage, current limits, and overheat protection. Some can input and output AC or DC, at a configurable frequency and sometimes waveform. Some offer the same galvanic isolation that a transformer offers too.
The core of a switched mode supply usually is a transformer, or at least an inductor, but the key difference is that it operates at far higher frequencies than classic uses of transformers, which allows them to be far far smaller, and therefore cheaper for the same power output.
Those properties are all positive, but there is one glaring negative: rf radiation. I know some ham radio station builders that will not allow any switched mode power supply on their property, including wall warts and smartphone chargers.
That's a problem, especially with low-end power supplies.
I designed a switching power supply a few years ago for a specialist application - driving 1930s Teletype machines which need 120VDC 60mA.[1] A switching power supply is a spike generator. Here's the schematic.[2]
This is reasonably RF-quiet. The transformer of the switching power supply is a toroid in a metal can, so you don't get too much RF from the transformer itself. But that's not where it usually comes from. The important thing is to keep spikes out of both the input and output wiring. That's dealt with by using LTSpice to simulate the circuit, and adding small capacitors and inductors until the spikes have disappeared in both voltage and current. At the output end, note the snubber C7, R1, D10, and D11, to soak up any spikes from the inductive load, and L2, to soak up output side current spikes. There's L1 and C12, to soak up kickback from the switched input side of the power supply. Plus C10 at the power input, which is from a USB port. They're all tiny surface mount components. The inductors are ferrite beads in surface mount form.
So there are eight extra components, just to prevent unwanted RF generation.
The LTSpice simulation shows that they're all needed. The simulation was used to choose the values.
This is why good switching power supplies have more parts than bad ones. You see that in teardown videos.
Are you saying large Transformers 1 mva, 10 mva, 100 mva, 500 mva are obsolete and should be replaced by switched mode power supplies? What mva is the threshold?
For new installation, yes, for any size a switched mode supply will usually be better in all dimensions. For the largest sizes, you can't buy them off the shelf, and there design costs may dominate. But after the thing is designed, in component costs, switched mode will win. Everything scales linearly with kVA, so there is no economics crossover point for the fundamental materials.
Eventually it will be worth switching out old transformers - they contain a massive amount of valuable copper and quite valuable steel, and their lower efficiency means every year they remain in service they are wasting $$$'s of electricity.
Transformers in cities can often be replaced with much smaller switched mode units underground, allowing the building housing the old transformer to be rebuilt as luxury flats to make the project much more profitable too!
Large power transformers have efficiencies in the 98-99.75% range.
I don't doubt switch mode could be smaller and cheaper up to some size, but I am struggling to see transformers larger than about 5 mva being replaced with power electronics.
Solar farms etc have inverters in modules I believe 500 kva each - and of course the power electronics are necessary there, there is no substitute.
I have a 20 MVA transformer that is nearly at end of life and would be open to cheaper replacements.
For 5-20 MVA you're talking about 67 kV substations or similar, where a transformer costs in the low 6 figures. HVDC converter stations in the same range would cost somewhere around 8 figures, although that's mostly a guess- you typically need maintenance and supervision in a way that you don't with transformers. 1%+ downtime is pretty common, which absolutely sucks if you aren't a full grid and can't pull extra generation.
Yeah, but that price tag is mostly due to the fact that HVDC isn't a widespread technology yet. Once factors of scale come into play, the situation will look different and the prices come down.
Additionally, the price of copper is already at an/near the all-time high and it's not going to get cheaper, and the land on which huge transformers sit is shooting up in value... so in the end, market forces may push towards solid-state technology anyway.
They tend to be much smaller, lighter, more efficient, cooler and cheaper. They also have features like adjustable output voltage, current limits, and overheat protection. Some can input and output AC or DC, at a configurable frequency and sometimes waveform. Some offer the same galvanic isolation that a transformer offers too.
The core of a switched mode supply usually is a transformer, or at least an inductor, but the key difference is that it operates at far higher frequencies than classic uses of transformers, which allows them to be far far smaller, and therefore cheaper for the same power output.