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TIDA-010232: Can it be applied in AC split phase L/N insulation?

Ryan Lin
Prodigy 10 points
Part Number: TIDA-010232

Tool/software:

Hello TI supports,

The reference design about this product is using in DC Insulation monitor. I'm wondering if this circuit can be applied in AC L-N split phase insulation monitor as well?

Currently, I have AC split phase 240volt PCB. And the SP/SN relays are at line/neutral. But the calculation of equation (13)(14) in the reference is weird.

The number is like Vn=202volt, Vp=372volt, Vdc=161volt. (I switch the relay at the AC angle 90 degree). And then one of the Riso is negative. Please help me if any suggestion or what part of detail should I provide? Thank you in advance.  

  • 0
    TI__Expert 4400 points

    Hi,

    Thanks for reaching out and sorry for the delay during the holidays.

    First, a few  general comments on AC line insulation monitoring.
    This approach can work for AC insulation monitoring in certain conditions. The main challenges for insulation monitoring on AC lines ate the Y-CAPS which are typically present on the AC Lines. If these caps are big the cause an impedance parallel to the measured  insulation resistance which will impact the the accuracy. For y-Caps smaller than 5nF the impact is limited and it can be ignored. Otherwise this needs to be compensated in away.

    in your comments the first thing I recognize is that VDC is smaller than VP which should never be the case.
    In the AC case VDC needs to be the instantaneous value of the AC voltage at the time of the measurement of VP or VN.
    You should trigger the measurement at the peak of the AC voltage. So in your case VDC should be around 340 V. 
    The voltages VP and VN should always be smaller than VP. 
    Please refer to figure 2-14 for the recommended timing of the sampling of VP and VN during the AC cycle and refer to figure 1-5 and 1-6 for the equivalent circuit during measurement of VP and VN. The DC source drawn in 1-5 and 1-6 has to be replaced with the AC grid and VBUS+ and VBUS - has to be replaced with L and N.

    Hope this helps.

    Best regards,

    Andreas