Coordination of the Back Flashover Probability of HVAC and HVDC on a Hybrid Transmission Tower

The demand for power transfer has increased throughout the green transition, especially as power generation is becoming increasingly decentralized. However, building new transmission lines and towers is met with public opposition. One
option to increase transmission capacity while minimizing the erection of new towers is to use hybrid HVAC-HVDC multicircuit towers. If not carefully designed, considerably more back flashovers could occur to the more vulnerable DC circuit. This paper investigates the effect of a change in insulator size on the ratio of back flashovers between AC and DC circuits on the same hybrid tower by using a PSCAD model with HVAC-HVDC hybrid towers. A back flashover ratio calculation method is developed and used in combination with an algorithm to provide a DC insulator length based on a predetermined back flashover ratio. The algorithm allows for faster design of the insulator sizes for a multi-circuit tower, coordinating the ratio of back flashover probabilities to either the HVAC or the HVDC circuit.