Experience in superimposed impulse voltage testing of HVDC cables using coupling capacitor

The increasing deployment of HVDC cable systems, driven by the global energy transition, necessitates robust testing methodologies capable of accurately assessing both electrical and mechanical performance under actual operating conditions. Among these, the superimposed impulse voltage test represents one of the most critical procedures for evaluating insulation integrity in HVDC cables. This study presents a validated EMT model of the test circuit based on actual equipment parameters, thereby enhancing the reliability and predictive accuracy of the proposed simulation framework.
A central aspect of the work was the practical implementation of the coupling capacitor using a symmetrical charging impulse generator, with a comparative analysis between the manufacturer-recommended configuration and a proposed configuration employing additional stages of the impulse voltage generator. The EMT simulations, supported by experimental measurements, confirmed that the proposed configuration provides lower electrical stress on the coupling capacitors and a more favourable voltage distribution by utilizing a greater number of capacitors.. Additionally, the proposed configuration simplifies laboratory operations by eliminating complex spark gap adjustments, thereby reducing operational risks. Moreover, this work serves as an important reminder of the value of EMT simulations. Before conducting the actual test, a 10-hour simulation, or longer to account for time to perform superimpose test, can be performed to verify the feasibility of the test and to check whether the voltages will exceed allowable limits.
Nevertheless, despite these advantages, the simplest and most robust solution remains the use of an external, standalone coupling capacitor. Although it requires additional laboratory floor space, this approach reduces complexity, minimizes risk, and is more cost-effective than employing larger impulse generators for dual functionality. Ultimately, the choice between configurations should account for laboratory space limitations, equipment availability, and the balance between test reliability, operational simplicity, and cost.