On the electromagnetic coupling of AC and DC circuits on hybrid transmission towers

Transmission system limits, originating from right-of-way permission processes for new corridors, can be surpassed by erecting new circuits in close proximity, or even on common structures. Especially for long distance bulk power transfer, high voltage direct current technology promises superior features. Adding a circuit to a transmission corridor is one method of significantly increasing power transfer capability. Converting an existing AC circuit for DC operation is another method that additionally decreases investment in new lines and towers. Consequences of such application are various AC/DC interaction phenomena on either AC or DC lines for both steady and transient conditions. This paper presents a study on AC/DC transmission system interactions for a hybrid tower configuration. In normal operation DC voltage showed no significant fundamental AC frequency component, while induced transient overvoltages displayed notable levels.