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Using Electronics to Measure Electric Potential around a High-Voltage Insulator

Discussion in 'General Electronics Discussion' started by TomP123, Mar 27, 2017.

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  1. TomP123


    Mar 27, 2017

    I am wanting to measure the electric potential around a high voltage insulator, using some electronics circuitry. To begin, I have a probe which is suspended at a particular point on the insulator and the insulator is raised to 100kV. Assuming a uniform potential distribution, if the probe is placed roughly half way down the insulator, then the probe should be raised to around 50kV.

    I have also made an electronics circuit to pick up the voltage from the probe. The circuit is a battery powered (floating) device which consists of a resistor divider network (to scale down the voltage by a ratio of 1000) and then a DMM to measure the signal.

    The problem however, is that the circuitry has its own ground (from the batteries it is powered from) and therefore has a different ground to the probe voltage (this is referenced to the HV ground). I cannot find a way to measure the probe voltage using isolated electronics circuitry, can anyone suggest a solution?

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    As I see it, any resistive divider is going to load down the input. Added to that, it will provide a conductive path that might cause the insulator to flash over.

    Detecting the gradient of the electric field might be easier. Google "electric field mill" for some information
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    That's becasue it is, afaik, not possible.
    Voltage is the difference in electric potential between twopoint. To measure voltage you therefore need to probe both point. In your case one point is HV ground, the other is the sensor.
    As Steve mentioned using a resistive divider will present a load to the sensor's output and therefore will change the measured voltage. You could minimize the effect by using veeeeery large resistors (in terms of resistance, not necessarily size).

    However, there is still the issue of safety: When your sensor slides along the length of the isolator, it will experience voltages from 0 V (at HV ground) to 100 kV (at the other end). Your sensor-divider-instrument setup needs to be safe for handling this range of voltages. A dangerous undertaking even for someone with experience.

    I strongly recommend you leave this to experts and get a specialized probe suitable for this application.

    It is for that reason that I will close this thread.
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