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Original question:

DRV421 application

DRV421: Residual current measurement in AC distribution system 1Phase or 3Phase

Tirumalesh Peedi
Prodigy 30 points
Part Number: DRV421

We would like to use  DRV421 device to measure Residual current in AC distribution system. We only wants to measure residual current in the range of 6mA to 100mA and display the value(AC/DC). There is no need for measuring line currents. Actual line current would be less than 32A (Single phase /3Phase).

Can DRV421 be used for this type of application. If yes, please share reference designs or design calculations if available.

Regards

Tirumalesh

  • 0
    TI__Mastermind 29710 points

    Hello Tirumalesh,

    We do not have any reference designs and there are many design challenges to use the DRV421 in this case.

    This measurement will be very difficult to do and there will be a few issues you will need to deal with.  First the DRV421 has an offset of 8µT.  If your core generates a field at the DRV421 at about of 500µT/A then this would create an error from offset of 16mA.

    Offset = 8µT, Core Gain 500µT/A;  Offset error = 8µT/(500µT/A)= 16mA

    The core design will be very important for several reasons. The core would need to reject outside magnetic fields from other sources such as earth’s magnetic field neighboring currents. Also magnetic coupling between your primary conductors to your air gap could cause error. For example if one current conductor is closer to the air gap then the field generated from that conductor could couple to the sensor and not give accurate results.

    The inductance needs to be 100mH and this will be determined mostly by the air gap size and your number of windings. You cannot drop your number of windings and get the inductance required. Also increasing Rshunt you need to concern yourself with Stability.  See Application Note

    The degauss may not be good enough and you would need to create your own degauss circuit. Also when increasing Rshunt the current will not degauss you core.

  • 0 in reply to Javier Contreras4
    Prodigy 30 points

    Hi Javier,

    Thanks for the detailed explanation and inputs. 

    We are afraid as we need to detect 6mA current and flag alarm. Please suggest any alternate solutions that can be used to detect currents of magnitude less than 6mA.

    Also, in earlier posts, we understand TI is working with Mangetics Vendors for development of Core. Can you please give us the references(Magnetics Vendors) for development of core.

    Thanks,

    Tirumalesh 

  • 0 in reply to Tirumalesh Peedi
    TI__Mastermind 29710 points

    Tirumalesh,

    I am afraid I do not have a simple solution available at this time.  You will run into all the challenges I mentioned above including stray magnetic fields you will need to shield from.

    There was Sumida we had worked with in the past for a design but there are many others.