How to set residual/remanent flux/magnetism?

[krunom]

Hi, I am carrying out some switching measurements on a one-phase transformer and it would be very important that I could set the same residual flux before each measurement.

For instance, could I use DC-source so that through the winding flows DC-current that would set residual flux to some value? Furthermore, if I decrease the DC-current to zero, would the residual flux decrease on zero also?

Namely, it is not clear to me does the flux (after aplying DC-current) depends on residual flux which existed before the applying?

 

[MagMike]

I would suggest running full (DC) current into the transformer, turn the current off, reverse the leads and then run 90% (or some other arbitrary value) of full current. Continue the process (reversing leads, running at decreasing power levels) until you reach the desired flux level.

This method would not be exact, but by doing the full pulse first, you'll erase residual flux history from the transformer.

Mike

 

[fluxedup]

You have two options and it depends on your ultimate goal for your measurement. If you want to see the effects of residual magnetism, you can saturate the core with a DC current and then remove it (be careful of the inductive spike) The core will remain at the maximum residual flux for your tests. If you then want to demagnetize the core, the easiest way to do this is to simply use an AC signal. Simply saturate the core with an AC signal and gradually decrease the voltage to 0 and you will end up with a non-magnetized core. (A variac works well for this) This will give you the two extremes and if you want to find some point inbetween to reliably set your residual flux then start with a demagnetized core and then run a specific DC current through the coil to bring the core to the desired remanent point. After each test, you can then demagnetize the core with AC and then apply the same DC current to return to the start point.

dave