measuring high voltage/power

[FvM]

"Measure" (=monitor the occurance) of nanosecond waveforms with a spark gap? Please review laws of physics and reconsider.

 

[newbusofborg]

I'm talking thousands or tens of thousands of volts with the added complication of possible nanosecond pulse durations.

I'm just curious how you guys would go about getting an idea of relative output values.

Here is my thought, please comment.

I don't want to take a chance on burning out an oscope so I thought this might work.
You could measure voltage with a variable spark gap.
As for power you could run the output through some sort of disposable lamp like a 300w incandescent or even an automotive bulb and then measure that with a photocell of some sort.

Any suggestions for a bulb other than the incandescent?

Any other measurement methods that don't involve expensive equipment?
I'm not looking for high accuracy.

 

[D.A.(Tony)Stewart]

Here I used HF CT to measure current on ground strap and large Capacitance transformer ( not shown) to measure 50~100kV voltage impulse with C ratio that scales voltage down to safe levels for 50 Ohm termination inside scope. High quality coax is critical. Here V impulse is 10V input 50 Ohms or 2 watts which when concentrated in a dust particle in oil filled transformer is enough to create a finite amount of Hydrogen.

Result below is a partial discharge PD inside insulation of 5MVA transformer, known to operate normally except for rising H2 levels dissolved in oil.

Here the waveform was probably 10ps wide or less but limited to <1ns risetime from scope @ 300MHz.



In physics they use integration method with scintillation detectors. In Spectral Analyzers they use quasi-peak detectors which are not fast enough.
There are many other methods to measure peaks and duration by integration methods. Transient voltage using tapped bushings for capacitance ratio is common. We call these Cap transformers as opposed to magnetic transformers.
To detect voltage transients , easy method is to use scope ground shorted to tip and create a loop antenna for near field measurements. Resonant frequency of loop can be determined from size.
Coax loop gives better results/

If you have Hipot or HV DC generator you can measure breakdown in air, oil or any fluid and effects of contamination by PD measurements before breakdwon occurs using any scope nearby with shiorted loop nearby or around ground wire.



Be care what you dig for. High Vdc E-fields accumulate voltage and reach very far away.

 

[chuckey]

If you have a light sealed, but variable spark gap, you could include a fast photo cell which can then trigger a pulse extender, so short pulses can be detected.
There is little prospect of measuring the power in high voltage nano second pulses. One Heath Robinson way would be to allow the arc to occur in an acoustic chamber with a microphone in it and some form of peak holding volt meter on the mic. So you allow a few arcs from your unknown source, which you then replace with a capacitor charged up to the same voltage. Select capacitor for same acoustic voltage. Then do your calculations.
Frank

 

[newbusofborg]

Thanks Frank!

sunny, whats hf ct?

 

[D.A.(Tony)Stewart]

Thanks Frank!

sunny, whats hf ct?

High frequency magnetic current transformer (gapped torroid ) expensive..... All you need is one turn around ground strap for 1ns pulses. no need to buy CT.

Basically a loop antenna or shorted probe wire is easiest method. The other common methods are stripline antenna, and tiny terminated dipoles.