Improvement of the INRiM calibration capabilities for lightning impulse voltages from 200 kV to 600 kV

In this paper, an improvement of the calibration measurement capabilities (CMCs) of the Istituto Nazionale di Ricerca Metrologica (INRiM) for measurements of Lightning impulse (LI) voltages from 200 kV to 600 kV, is proposed. This improvement is the result of a more detailed characterization of the INRiM measurement system for LI measurements. The INRiM LI measurements of the most critical waveforms at voltages up to 600 kV for the EURAMET.EM-S42 comparison were submitted to a refinement with a discrete deconvolution method. The comparison results were then recalculated by inserting the INRiM measurements, both with and without deconvolution, (the latter for less critical waveforms) and the updated uncertainties. The INRiM measurements after recalculation were still in agreement with the comparison reference value, even for short impulses (0.84 µs), where the size of the used divider was not optimal. The recalculation did not affect the degrees of equivalence of the other participants and the consistency of the comparison. The new INRiM uncertainties range from 0.5 % of Ut (test voltage) for the long impulse at 600 kV to 2 % of T1 (front time of the impulse) for the short impulse at 400 kV and 600 kV. A validation of both the new uncertainties and the selected discrete application of deconvolution is also proposed, together with a verification of the compliance of the INRIM measurement system up to 600 kV with the requirements of a reference system.