Insulation Coordination Process for HVDC Converter Stations: Preliminary and Final Designs

Insulation coordination of hvdc converter stations is a critical part of the overall system design process. Insulation levels for system components must be determined, and a scheme must be established for protecting equipment constructed to these insulation levels. This task involves consideration of several key factors and requires significant engineering effort. The purpose of performing an insulation coordination study as part of the design process for an hvdc transmission system is twofold: * To establish the maximum steady-state, temporary, and transient voltage levels to which the various equipments within the terminals will be exposed and thereby determine the required voltage withstand capabilities of the equipment. * To determine the characteristics of the protective devices (i.e., surge arresters) required to ensure that equipment is not subjected to voltages in excess of the specified protective levels. This involves not only defining the number and location of the surge arresters within the system, but also determination of the protective and durability requirements for each surge arrester. Insulation coordination for hvdc converter stations is, in principle and methodology, similar to insulation coordination of ac substations. Differences exist primarily due to circuit topology, involving series-connected arresters between ungrounded terminals, the complex hvdc control system-power system interactions, and the presence of large var sources and harmonic filters. This paper reviews some of the major findings of an EPRI-funded research project [1] that developed a handbook for insulation coordination of hvdc converter stations.