Upgrading AC transmission to DC for maximum power transfer capacity

The paper describes current developments for upgrading of existing AC transmission lines for substantial increase in power transfer capacity by a new concept of conversion to HVDC transmission. Traditionally, such a conversion has been contemplated as being three phase AC to bipolar DC. Recent patents by one of the authors have introduced the tripolar DC transmission concept, which maximizes the utilization of all three phase conductors and improves N-l operational constraints. Conversion consideration issues, e.g. selection of DC voltage rating, the need for re-insulation, etc. are investigated. The paper provides an overview of an Application Guide that is being prepared by EPRI for transmission engineers and planners contemplating upgrading AC transmission lines to HVDC transmission