solid state voltage stabiliser

http://en.wikipedia.org/wiki/Voltage_regulator

Having trouble with Google, eh?

It takes unstable voltage in...and puts out a stable voltage.

It does this using solid-state components.

Really quite ingenious.

Since the extra low voltage and current version has been explained in post #1 here is an example for the high voltage high current version

33kV Grid solid-state voltage stabiliser

As you can see there is quite a difference between the two.

I think you need to define the nature of your question better. There is a difference between a voltage regulator, and what a lot of people are selling as "voltage stabilizers" or "voltage optimizers", the latter two of which are often part of an "energy saver" scam.

In essence, they monitor the incoming 3 phases and use SCRs to phase back the RMS voltage of the two higest phases to the level of the lowest. In other words they reduce everything to the lowest common level. It's a very old scheme despite their saying they "invented" it, it's been around since the late 1960s or early 1970s as far as I know. The "energy saving" idea is that unbalanced 3 phase voltage creates what are called "negative sequence currents" in 3 phase AC motors, which create counter-rotating torque and increase the current consumed by a motor for a given amount of work performed. The problem is that it looks good on paper, but in reality it reduces the motor output torque as well so it also DECREASES the amount of work the motor does. If it is doing something like pumping water, it pumps less and therefore has to run longer to accomplish the same task. There are a very FEW applications where it makes sense, but not enough to justify buying one in my opinion.