Where did you get those costs?
They seem a little out of proportion.

Look at a transformer catalog or detailed specifications sheets, and the answer will become clear. Size, mass, and complexity make a difference. Also, there may be other differences between the models compared. BUT a single 3-phase transformation CAN BE DONE with three single phase transformers.

 

The reason for the higher voltages, and three-phase power, will be clear when you do the math for a 20 HP or a 50 HP electic motor. Use a textbook for the examples, not an online fraudster site.
A revelation: not everything you read on the internet is correct!! In addition, some stuff is totally false.

Really? I spent 25 years in that facility. Really interesting was the 3 phase 4160 VAC pumps in the pump house. The old Amplidynes had 40 and 50 HP motors, those were 3 phase 480 VAC.

Ron

 

BUT a single 3-phase transformation CAN BE DONE with three single phase transformers.

Often:
Actually a 3 ph transformer is made up of three separate 1ph ver, on the same frame.

 

There is an even weirder power delivery, the Scott-T connection.
In the city of Monterrey, Mexico, American investors installed the very first electrical grid in the early 1920s. For some reason(*), they used a two-phase system and continued to do so for a few decades. Eventually the superiority and ubiquity of the three-phase won the day, but the question was what to do with the legacy distribution lines? So they used the Scott connection to marry the two different systems.

Up until the mid 1980s one could still find in the old town, el barrio antiguo, many streets where this weird system was still being used. One knew that a location was being supplied with a three-phase 220V line-to-line Scott connection, because on a pair of the phases each would show 110V to neutral, but the remaining phase would be 190V to neutral!
Ask me how I found out!
My understanding is that everything nowadays has been upgraded to proper three-phase.

(*) never found the real reason, but back then an engineer told me that they had installed surplus equipment removed from somewhere else.

 

There is an even weirder power delivery, the Scott-T connection.
In the city of Monterrey, Mexico, American investors installed the very first electrical grid in the early 1920s. For some reason(*), they used a two-phase system and continued to do so for a few decades. Eventually the superiority and ubiquity of the three-phase won the day, but the question was what to do with the legacy distribution lines? So they used the Scott connection to marry the two different systems.

Up until the mid 1980s one could still find in the old town, el barrio antiguo, many streets where this weird system was still being used. One knew that a location was being supplied with a three-phase 220V line-to-line Scott connection, because on a pair of the phases each would show 110V to neutral, but the remaining phase would be 190V to neutral!
Ask me how I found out!
My understanding is that everything nowadays has been upgraded to proper three-phase.

(*) never found the real reason, but back then an engineer told me that they had installed surplus equipment removed from somewhere else.

I recall that quite a few years ago I had to work on prototype model cars for two weeks in Mexico City. Yes, the power was strange to me, but fortunately my laptop power supply was set for universal power, so I had no problems with that.

 

Look at a transformer catalog or detailed specifications sheets, and the answer will become clear.

This from Google AI:
So is that not correct (clear)?

AI Overview

A new 100 kVA transformer generally costs between $1,600 and $7,000 for oil-immersed units and $2,000 to $8,000 for dry-type units, with single-phase and three-phase units of the same 100 kVA rating falling into similar initial price brackets ($3,500 to $5,000 on average for standard pole-mounted or pad-mounted distribution models)

 

The Mexico City electric grid was financed and engineered by a British company.
That meant it was powered at 50Hz, while the rest of the country was 60Hz.
In the late 1960s the Mexican government unified the whole country to 60Hz.

 

Where was the power generated?

 

Within Mexico City’s metropolitan area, which wasn’t connected to the rest of the country.

 

As for google pricing, it is unwilling to look at the same sources as I use, and so it always arrives with totally different answers from totally non-related sources. Perhaps I offended it on some occasion, so now it never stays on my topic when asked about anything, for me.