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Mechanical circuit breakers (MCB) are the limiting component for current injection HVDC circuit breakers. Improving their interruption performance reduces the requirements for capacitance and inductance needed in the injection circuit and thus space use and costs. Higher interruption performance can be achieved by creating a period of low current gradient before zero crossing in the MCB, for example by using a saturable inductor (SI).In this article, the impact of duration and steepness during the low current-gradient phase is linked to arc parameters of the investigated model gas circuit breaker. It is shown in a scaled experimental setup that an optimum design of the saturable inductor can be derived from arc time constant and interruption limits for constant current gradients. This optimization results in a considerable increase of interruption performance.Based on experimental results, the feasibility of implementing a saturable inductor in a full scale HVDC circuit breaker is demonstrated by means of simulation. Using an improved injection scheme, the stresses for the mechanical interrupter can be reduced significantly in terms of rate of rise of current before and voltage after zero crossing. As a result, it is possible to scale down the components of the injection circuit, making the topology more economical. The reduced interruption requirements might also make it possible to use a single gas interrupter instead of a series connection of vacuum interrupters, reducing the complexity of the mechanical switch., High Voltage, 4 (2), ISSN:2397-7264