Main Issues Regarding HVDC Overhead Transmission Lines Insulation Coordination: VSC Technology and Dedicated Metallic Return

This paper evaluates how VSC technology and DMR use affect tower insulation coordination compared to traditional LCC (Line Commutated Converters) methods. It considers both internal and external overvoltages, dielectric strength, pollution, and weather in optimizing tower design. Key factors include the impact of terminal components, such as filters and smoothing reactors, on internal overvoltages resulting from pole short-circuits, as well as the role of various converter types (half-bridge, full-bridge, hybrid).

Insulation coordination for neutral conductors, specifically, DMR insulator configurations under lightning and internal overvoltages, is assessed due to the risk of induced voltages exceeding insulation levels. Both bipolar and monopolar operations are simulated, focusing on how protective devices like spark gaps and surge arresters impact overvoltage limitations in

DMR installations.

This paper presents a new approach to selecting tower line insulation for operating voltages, considering pollution and wet conditions, with results from laboratory tests on dielectric strength. The discussion covers glass, porcelain, and composite DC insulators, recommending suitable types and numbers based on regional pollution and moisture. Steps for optimizing

HVDC tower configurations are proposed, using statistical risk-of-failure methods to determine insulation distances and account for withstand voltage. These findings may enhance current standards, highlighting the need for ongoing evaluation of new components in insulation coordination.

It is important to emphasize that this contribution is the genesis of the Technical Brochure under development in the WG C4.73