Three phase full wave bridge rectifier

[cj62565]

Hi,
I was asked in school, if I have 480vac going in and 630vdc coming out, how would I come up with this dc figure. I was not given any other values, and I'm comoing up with around 678vdc. There would be some voltage drop associated with the diodes but that is minimal. Around 4.2v. So I know thats not the reason for the drop of around 48v. This is not a test or homework, but just something my instructor asked at the end of class.

CJ

 

[RCinFLA]

Are we talking about r.m.s. effective D.C. ? There is ripple associated with three phase full wave rectified D.C. The rms D.C. would not equal peak value of AC unless there is a filter cap on output to keep the peak.

 

[Sceadwian]

Doesn't this have something to do with the phase angle difference from each leg?

 

[RCinFLA]

Okay, you forced me to do the calculation.

Ignoring rectified voltage drop.

480 vac rms three phase full wave rectified

Peak = 678.82 vdc.

Minimum = 587.88 vdc

Ripple = 90.94 vpk-pk

D.C. rms = 648.62 vdc.