Adjustable Injection Currents: The Benefits of Controllable Inductors in Current Injection HVDC Circuit Breakers

Abstract

Economic and robust high voltage direct current (HVDC) circuit breakers are a strategic technology in the development of next-generation power transmission. Current injection circuit breakers require fewer complex components than other technologies, making them economically attractive. The limiting factor, however, remains the high current and voltage gradients which occur at zero current during the interruption of low fault currents. This paper investigates a novel current injection topology that generates adjustable injection currents. This is realized by controlling the injection circuit inductance via a non-linear magnetic core. The inductance varies according to the core's saturation state, which is manipulated by at least one control winding carrying a quasi-DC current. By holding inductance low at the beginning of injection, a minimal time-to-interruption may be achieved. Increasing inductance shortly before interruption reduces both the current gradient and ensuing transient voltages, thus reducing stresses on the mechanical interrupter. In this paper, a simulation model for the proposed controllable inductor is developed and compared to results of a scaled-down experiment. On this basis, the topology is dimensioned for the use in a 320 kV network. The conducted simulations illustrate both feasibility and advantages of the novel topology compared to a reference current injection circuit.