Knowledge of lightning impulse (LI) voltage distribution over transformer windings during the design stage of the transformer is very important. Specific design differences in inductive voltage transformers make the transient analysis approach different to the approach to the power transformers. In this paper, a methodology for acquiring lightning impulse voltage distribution over high-voltage (HV) winding of inductive voltage transformers is presented and evaluated. Resistance, inductance, and capacitance matrices are calculated using the integral and boundary element methods (BEM) approach. Additionally, in order to improve the capacitance matrix solver, adaptive cross approximation (ACA) is applied. These parameters are then used to solve the equivalent circuit model in time domain. In order to evaluate the methodology, an experimental and numerical investigation of the layer discretisation, iron core influence, and accuracy of the proposed methodology is performed. The comparison of numerical results with measurements confirms the validity of the methodology.

For calibration of the environmental monitoring field meters, a reference standard of electric field strength based on parallel plates is established in the Primary electromagnetic laboratory FER-PEL in Croatia. The plate system incorporates guard ring electrodes with a set potential distribution to improve field uniformity within the center calibration volume. In addition, the concept of the Kelvin guard-ring electrode applied to one of the plates allows the measurement of the displacement current through the guarded plate system. The reference electric field strength is derived from the nondimensional field distribution factor, calculated from the ratios of the system’s quantities, and the measured voltage and capacitance of the plates. The elaborate uncertainty budget confirms expanded uncertainty of 1.2 % for generating low-frequency reference fields up to 20 kV/m, with exclusively electrical traceability.

A lightning current measurement system for wind turbines was developed and tested in the High Voltage Laboratory at the Faculty of Electrical Engineering and Computing, University of Zagreb, to determine actual distributions of lightning current parameters in a particular wind turbine area. The output of the measurement system is a waveform of lightning current. The measurement system consists of two current sensors with different frequency and amplitude ranges and a real-time controller with two digitizers and a GPS module. The current sensors are Rogowski coils connected to integrators with coaxial cables. The prototype was installed on a wind turbine in a high winter lightning activity area. The current stage of development involves integrating the high-speed camera into the prototype measurement system to obtain the visual confirmation of the waveform measurements and help categorize lightning strikes into downward or upward strikes. The camera control application was developed in LabVIEW. The camera was set to trigger by the real-time controller. Also, a redundant trigger occurs when there is a change in motion in the camera frame in case the prototype measurement system fails to register a lightning strike and therefore fails to send a trigger signal to the camera. The camera control application was tested in the High Voltage Laboratory by recording a flashover in a spark gap and a flashover on the insulator.