Hi,

The circuit attached is just a fragment of a whole design. It shows a three phase rectifier with 3 filter inductors at the input side, and a capacitor, a MOV, and fuse at the output side. I wonder what the differences are in protecting the AC side vs the DC side. I've seen designs where they use 3 fuses, 3 MOVs at the input side. This seems like an increase in cost if we compare it to using just one fuse and one MOV at the DC side. I've also seen the use of TVS diode after the bridge. What approach would you use and why? Are there actually differences whether we choose to protect just one side or both?

 

Having fuses on the mains input will protect again further damage should a rectifier diode or associated parts fail. The fuse on the output will only blow with over current in the load.

 

In many HV 3ph rectifiers that are mains or AC mains derived, it is definitely normal to include fusing in each phase, this protects from lightening induced spike etc on the supply.
If this is directly from the output of a alternator, Auto etc, then it is not customary to do so.
Max.

 

So how can this circuit be improved in terms of protection? What can be added/removed? I don't know if TVS diode after the bridge would be a good idea to help against voltage transients. In this case the MOV is in the DC side for that reason, right?

 

Where is the 3 phase derived from? What voltage?
Max.

 

It comes from the grid through isolation transformers. The line to line voltage can go up to 415 VAC.

 

All the three phase full wave SCR/rectifier bridge drives/supplies that I have worked on in industry, usually had fast sweep-Rectifier fuses in each incoming phase.
Max.