three phase low volts use?

[sephiroth]

why are three phase low voltage power supplies used for outputs greater than 2kW or for a low output ripple?

 

[sephiroth]

any input guys?

 

[Skogsgurra]

The rectifier in a three-phase unit outputs a voltage with only a few percent ripple and needs very little smoothing. The reason is that the three phases overlap so that the rectified voltage never goes to zero.

A single phase rectifier doesn't have that property. The voltage goes to zero 120 times/second (US) or 100 times/second (Europe). That's a lot of ripple. It can be smoothed out with capacitors, but ripple increases with load.

A three-phase unit has a constant, low ripple that is almost independent of load.

Gunnar Englund

http://www.gke.org

 

[sephiroth]

so is that because of the phases being 120 degrees apart the sine wave doesnt go down to zero as one phase is going from full +ve to -ve the next one is just going to full +ve?

 

[Skogsgurra]

Yes, that's right. If you draw a diagram over the three voltages and then "fold" the negative ones up, you will get a pretty good picture of what a rectified three-phase voltage looks like.

Gunnar Englund

http://www.gke.org

 

[sephiroth]

brilliant thanks

 

[itsmoked]

That and single phase is usually an outlet that can only supply 1,500W without extra hassles.