Constant AC voltage supply

[Variac200]

I want to design a voltage optimisation device using a transformer approach. Is it possible (practically) to control the taps such that the output voltage stays at a CONSTANT value irrespective of the supply voltage?

Need wild Ideas.
Thanks

 

[Skogsgurra]

Does it have react very quickly to input voltage changes? Or is it acceptable that output voltage deviates for around a second?

In the former case, a resonant constant voltage transformer does the job.

In the second case, there are Variacs with servo motors that keep the output voltage constant within one or two volts when input changes. Is that why you chose your nick?

Of course, it also depends on what power levels you are talking about. If more than a few kilowatts, none of the above is practical.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[DRWeig]

Constant for how long? 5 milliseconds, 5 seconds, 5 days? Amps? Volts? Three-phase or single-phase? Load varies how much from lowest to highest? Load varies from lowest to highest how fast? Are you powering a city, a hospital, a house, a window air conditioner, a toaster, a desk lamp, an LED night light?

More info please!

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[DRWeig]

Forgot to ask: How much will the supply voltage vary, and how fast?

Skogs, you were typing same time I was. I agree with a resonant transformer for quick blips.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[VEBill]

We once had one of those servo controlled variac systems. Three phase, three variacs, all on a common vertical shaft. Each variac was large, about 50cm diameter. The whole system was in a six foot tall, 19-inch rack. I seem to recall it was rated at 15 amps per phase, but that's a vague memory. It was a monster.

These days UPS systems seem to be default solution. In spite of the fact that they're a pain and seem to fail almost as often as the power.

 

[VEBill]

There's an old trick of using a spare winding (e.g. 6.3 volt filament winding) on the transformer to boost or buck the other secondary output(s). In addition to the buck, nothing, or boost options, one can employ a variable voltage.

The advantage of this approach is you're dealing with lower voltages. The disadvantage is less range (e.g. +/- 6.3 volts).

 

[Skogsgurra]

A combination of VE1BLL's idea and a triac controlling the primary of such a transformer seems to be a good compromise. Reasonable fast and without the large transients that plagues a regular "All Power" triac/thyristor version.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Variac200]

Thanks for the responses.

The idea is to keep the voltage at a fixed value of say, 230V despite changes in the supply. Ultimate goal is to save energy by keeping the voltage low instead of supply voltages that goes way high.

 

[Variac200]

Also should the supply voltage fall below the desired output, for eg 230V, mechanisms must operate to step-up the voltage. In DC-DC converters, SEPIC works exactly like that.

But I am thinking of using a transformer either with taps or some other mechanism

 

[ScottyUK]

Speak to Watford Controls. They make the servo-type regulators with some very high outputs. The larger ones probably use some sort of tapchanger rather than a variac - a multi-MW variac would be difficult to construct using the conventional brushed design.

 

[Skogsgurra]

A so-called "induction regulator" will do what you want. Without tap changers. Available in tens or hundreds of MW.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Variac200]

Great suggestions. Thanks for the lovely ideas. I am really interested in the operation of voltage optimisation devices that employ variable transformer circuits. Looking to build one. I dont want to consider servo-tap switching due to drawbacks such as slow response.

 

[Skogsgurra]

If you want to go without moving parts and fast response, a magnetic amplifier can also be used to control ten percent or so of your incoming voltage. Really simple and low cost.

Simple description here:

http://www.youtube.com/watch?v=lB3HBoKPbOQ

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

This book might be of interest

http://books.google.no/books?id=PuJ...ce=gbs_ge_summary_r&cad=0#v=onepage&q&f=false