# 3 phase rectification questions - Help needed!

#### Spow

Joined Apr 13, 2009
2
Hi there..
I have a problem with these two questions.. I need help in solving them, what equation do I use etc..

A three-phase half-wave rectifier circuit is supplied from a 120/208 V 3phase, 60 Hz source. Determine the average DC output voltage of the rectifier.

A three-phase half-wave rectifier circuit is supplied from a 120/208 V 3phase, 60 Hz source. What is the frequency of the output ripple voltage.

I spent 2h looking for the equations and explanation but with no results..

Can someone briefly explain how to solve them?

/Peter

#### jasperthecat

Joined Mar 26, 2009
20
Spow

Have a look at this

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

and the AAC AC tutorials particularly the polyphase systems

Are you having problems with rectifiers or 3 phase systems or both?

J

=^..^=

#### Sambodc

Joined Dec 22, 2014
1
I'm looking to answer some of my own questions on 3 phase rectification but i couldn't resist giving this one a go even if the thread is 5 years old!...
I don't know about the second question but i shall give the first one a try.

120V is the RMS phase to earth voltage whist 208V is the phase to phase voltage. 208V is the one we want to work with.

So if 208V is the RMS voltage phase to phase, we want to convert this into the maximum voltage for just one phase using the equation below.

Vmax = (208 x √2) / √3 = 169.831VAC The √2 is used to find the max V, whilst the √3 is needed because it is a 3 phase system.

We then use Vmax in the final equation.

Vdc = (3 x √3 x Vmax) / 2 x π = 140.449VDC

I know the final answer is off by 0.149 but i think it is right...

Sam