current transformers

[thedoc298]

I am using 3 current transformers 1000:1                     one for phase, one for ocd or current and the third for a scope to monitor.    Should the phase and ocd be in phase together and for the scope connection would I need some value of a load..?    I had them in phase and then I trimmed the wires and lost track.   Thanks

[flyingperson23]

I don't think the ocd and phase CTs need to be in phase. You probably want some sort of load (ie resistor) for the scope connection

[thedoc298]

I don't think the ocd and phase CTs need to be in phase. You probably want some sort of load (ie resistor) for the scope connection

Thanks for feedback.

[Mads Barnkob]

OCD feedback signal is converter to a DC level signal for the op-amp/comparator, so phasing does not matter. It could properly only mean if you switch off a single cycle later.

Load your monitor CT with the same shunt resistor as your phasing CT. So you see the same signal as your driver uses for ZCS.

[thedoc298]

OCD feedback signal is converter to a DC level signal for the op-amp/comparator, so phasing does not matter. It could properly only mean if you switch off a single cycle later.

Load your monitor CT with the same shunt resistor as your phasing CT. So you see the same signal as your driver uses for ZCS.

That is a good idea never gave that a thought, thanks. So close for test firing, be sending some videos soon

[davekni]

Load your monitor CT with the same shunt resistor as your phasing CT. So you see the same signal as your driver uses for ZCS.

Yes, I can see an advantage to that.  Or scope across CT burden resistor of driver.

There is one advantage to using a lower burden resistance for scoping, such as 10 ohms instead of 51 ohms of standard UD2.7.  In case CT inductance is low enough to add significant phase lead, scope measurement would be closer to actual current phase.