Improvement of the INRiM calibration capabilities for lighting impulse voltages higher than 200 kV

A lighting impulse (LI) is an impulse voltage with a front time shorter than 20 μs. Measurement systems for LI are established to evaluate dielectric stress of transient over voltages caused by lightning strikes, disruptive discharges to validate electrical components or devices. At the Istituto Nazionale di Ricerca Metrologica (INRIM) the “Laboratorio Alte Tensioni e Forti Correnti” (LATFC), equipped with two measurement systems for LI calibrations with two voltage dividers for voltages till to 200 kV and to 600 kV respectively, participated with satisfactory results, to the EURAMET.EM-S42 comparison of LI. An improvement of the INRIM calibration capabilities (CMCs) of LI voltages up to 600 kV is proposed. The INRIM measurements of the most critical waveforms at voltages higher than 200 kV are submitted to a refinement by means of a discrete deconvolution method. The comparison results are then recalculated inserting the INRiM measurements with and without deconvolution (these last for less critical waveforms) taking into account new uncertainties. The recalculation still shows a satisfactory agreement of the INRiM measurements with the key comparison value also for short impulses (0.84 µs) where the size of the used divider was not optimal. The recalculation does not affect the results of the other participants and the comparison consistency. The new uncertainties span from 0.5 % of Ut for the long impulse at 600 kV to 2 % of T1 for short impulse at 400 kV and at 600 kV. A validation of both the new uncertainties and of the discrete application of the deconvolution is also proposed