Hello,

Here's a scenario:

You have a 3 phase full wave power rectifier with one SCR open circuited (not firing).

What is the effect on the load?

Is it possible that this condition would cause abnormal heat buildup if the load was a battery being charged?

I'm also trying to understand the current flow - current rating relationship of the components. For example, we are using 3500amp SCRs w/ 4000 amp fuses on a piece of equipment that will conduct 8000+ amps (electroplating). How would I determine what current rating is required based on total current draw?

Thanks!

 

It would seem like you have gone from a 3 phase FWB rectifier to a single phase FWB. You should have a reduction in output voltage to about 73% of normal with a correspondingly lower current (If the load is unchanged). Your plating solution determines your current draw, correct? Take some voltage readings and give us some data to look at, as I'm just giving you an educated guess.

 

I doubt seriously that you would see a 73% reduction in output with one of 6 SCRs not firing. The SCRs are fired in pairs so you would only loose, at most, 1/3 of your output. In a plating operation, the ideal situation is to have a very smooth current supply, otherwise, whiskers and other bad things happen to the finish, if I recall properly. As for using the source as a battery charger, again, there would be a reduction of current every 120 degrees of your input frequency. Draw out your normal 3 phase rectified ripple signal then eleminate every third bump and you can see the effect.

 

Here are two simulations. First with all 6 rectifiers in the circuit and the second with one missing. As it turns out, you would get 4 bumps, miss 2, then get four, etc. In my first post, I forgot about full wave giving double frequency on ripple.. Old age brain toot.