Any idea what this step up transformer might have been designed for?

[rwgast_lowlevellogicdesin]

I found this transformer hidden on a shelf in my shop at work. It is massive, it probably weighs about 20lbs or so. The primary looks to be tapped for 120 parallel or 240 series.

When primaries 1&2 are connected to 120v

Secondary 7/8 puts out 210vac
Secondary 3/4 puts out 776Vac or 338Vac on center tap
Secondary 5/6 puts out 498Vac

I connected primaries 1&2 to a variac then connected secondary 3&4 to a beefy industrial equipment cooling fan by the time I got the variac to 120vac the fan was drawing 300ma but the voltage sagged from 776Vac to  380ish. The only secondary that didnt sag was the 210 coil. I figured for the massive size and weight the thing would have pumped out more current on the 776 coil.

Like I said im just wondering what in the world a transformer like this would generally be used for? It seems way to chunky to just power tubes. Judging from there web site it may be boat related? Anyways I looked up the part with no luck, but I did find someone selling a 5000Vac Charles branded transformer on ebay for $1800!

https://www.ebay.com/itm/304194163610?chn=ps&mkevt=1&mkcid=28

[T3sl4co1l]

Ferroresonant probably. ~800V is typical for the capacitor winding; a couple uF ought to tune it correctly, but more measurements would be needed to know for sure.  Or, any chance there was a capacitor nearby it?

Tim

[Andy Chee]

Yep I'd go with ferroresonant transformer as well.

https://www.emerson.com/documents/automation/product-guide-solahd-power-conditioners-en-us-99748.pdf

[Circlotron]

I'd also say ferroresonant. I used to work at Sola Basic in the late 80s and we manufactured them there. Also made sine wave UPSs up to 20kVA that had an SCR square wave inverter and one of these transformers to convert that into a fairly respectable sine wave.

[rwgast_lowlevellogicdesin]

No there was no cap around, it would be a few few uF at ~800v rating? I looked through the doc posted above, so it uses a tank circut to condition the power output??

If it means anything I do electrical maintenance of all kinds on a millitary base and it was tucked on a shelf in are fire alarm/traffic signal shop. It definatly could have came out of a huge UPS, what other equiptment would you find one in?

If I had an appropriate cap and connected it across the 776v coil, what would happen on the output coil? How would you figure out which coil is output vs compensation?

[rwgast_lowlevellogicdesin]

Ok i just read this

https://www.sunpower-uk.com/glossary/what-is-a-ferroresonant-power-supply/

Now i understand what these transformers do, my guess would be the 210 output is the main secondary to power 208Vac equiptment, maybe from a UPS or something. Id like to find an appropriate cap to test the thing out!