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I am conducting a project to measure Breakdown Voltage and would like to use a protection resistor, please see below.

enter image description here

When breakdown happens I will have something like

enter image description here

In this case the Power dissipated by the resistor should be P=I^2 * R, which gives

P=I^2 * R=(0.1)^2*1000000= 10 KW.

However, I cannot find resistors with that power rating. I have seen that some HIGH POWER RESISTOR will reach 500 W - 2000W maximum. Others only work for 71 W .

Am I calculating this in the right way?

Any ideas?

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    \$\begingroup\$ To get 100mA through 1M\$\Omega\$ you would need a voltage of 100kV. If you are powering it from 240VAC the primary current would be more than 40A, is that a correct description of your situation? \$\endgroup\$ May 19 at 18:35
  • \$\begingroup\$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. \$\endgroup\$
    – Community Bot
    May 19 at 19:29
  • \$\begingroup\$ What about 20 50 kOhm resistors in series, each one rated for 500 W and 5 kV? \$\endgroup\$
    – Uwe
    May 19 at 20:16
  • \$\begingroup\$ Do you really need a current of 100 mA? What about 1 mA instead? \$\endgroup\$
    – Uwe
    May 19 at 21:16

1 Answer 1

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If I do parse your question correctly, this is what you are trying to do:

  1. Test a cap with high AC-Voltages at a fixed RMS current of 0.1A
  2. Crank up the voltage until the cap fails
  3. Protect your circuit from short-circuit in the event of breakdown

As you have noted, a resistor with a 10KW power rating is kind of rare - you can of course get them custom build - money can buy almost anything.

My opinion: Make it simpler. Make sure to use a so called "impedance protected" transformer. Form a direct connection on the output terminals to the DUT-Cap. No current limiting is required in case of break down, as the transformer input impedance will be high enough to prevent blowing your power supply / trafo.

Please see:

ESE-Topic-1

IEEE-Articel

Siemens Appnote

Researchgate

Webarticel

Please consider: Lots of high power application notes - correct? This was turned out by google in thirty seconds. "impedance protected transformer filetype:pdf". Feel free to read these papers or go on the hunt again.

My assumption: Under the assumption, that the 10KW figure is far beyond your actual design requirements: Just get a 1:X impedance protected transformer an test you CAP. If the test current of .1A RMS is required make sure, that you understand the energy levels you are dealing with when forcing such a current on high voltage systems (Assuming >1kV) - sinewy stuff.

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