Straightforward E-field measurement in the MV/m range
When dealing with High Voltage (HV) devices, assessing the local E-field seems to stay a real challenge. However thanks to Kapteos E-field probes, making comprehensive measurement of any E-field component with a millimeter spatial resolution becomes a child’s play.
Experimental setup
In order to illustrate that assertion, we have built a classical setup with a grounded plate and a sphere connected to a HV source.
Kapteos measurement setup for this time-domain E-field measurement is based on:
a transverse E-field probe eoProbe™ ET5-LK,
an optoelectronic converter (OEC) eoSense™ LF to feed the probe,
a Digital Sampling Oscilloscope (DSO) to digitize the signal delivered by the E-field measurement system,
the high voltage device composed itself of a tunable high voltage transformer and the sphere-plane configuration.
Electromagnetic simulations
Such simple configuration can be easily simulated using any commercial EM simulation software.
For a 25 kVrms voltage value applied to the sphere, the E field is horizontal on the symmetry axis (r = 0) with a monotonous variation of its magnitude from the lowest value on the plane surface to the highest value on the sphere surface.
Experimental results
A gauge has been used for precise probe positioning with respect to the sphere in order to get an E-field strength of 1 MVrms/m.
Then the gauge is removed while keeping the probe in same position.
Different gauges have been produced in order to get different E-field strengths according to EM simulations.
For the closest probe position to sphere with 25 kVrms applied to this latter one, the recorded signal (in blue) is shown hereafter with a theoretical fit (dotted red) perfectly superimposed with the measurement.
As seen, the voltage transformer presents some little harmonic distortion. Indeed, from the fit, we get the table of signal fundamental magnitude (Ref) and harmonics given hereafter.
The signal magnitude has been measured for the three probe locations and for each kVrms about the applied voltage.
Kapteos EM-field measurement system keeps a linear behavior even for 1 MVrms/m E-field strength. Let us remind here that with such ET5-LK E-field probe, measurements can be carried out down to 200 mVrms/m, leading to a useful dynamic range higher than 134 dB! The dispersion of the experimental data is given hereafter.
Below 10 kVrms, the indicative voltage delivered by our high voltage transformer is rather inaccurate. This constitutes indeed the main uncertainty of the current measurements as the intrinsic measurement repeatability of Kapteos EM-field measurement system is only 0.15 dB.
Using best fits (horizontal dotted lines) for applied voltage higher or equal 10 kVrms, we get the table given below.
Key features of the E-field assessment in High Voltage devices
LF optoelectronic converter covering 6.7 decades of frequency: 10 Hz → 50 MHz
Perfectly adapted for: Partial Discharge, Corona Discharge, Dielectric Barrier Discharge, Lightning, Harmonic distortion assessment, Electrical transients, AC-DC HV converter...
ultra high dynamic range: > 135 dB
1dB compression point for ET5 probe response: > 1 MV/m
ultra high spatial resolution: < 5 mm
full dielectric, high permittivity, non-magnetic electric field probe
voltage withstand (direct contact to live metallic element): > 1 MV (unknown upper limit)