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With the development of modern power systems, the overvoltage protection and high current fast bypass of important electric equipment or parts in EHV grids put forward a great demand for high reliable fast bypass techniques. The triggered spark gaps now used in H.V. grids are still confronted with many difficulties. This paper proposes a conceptual design of a new multi-gap spark switch connected with a frequency-dependent network. The device is composed of series gaps and a chain RC network for producing frequency-dependent voltage distribution along the gaps. An even voltage distribution under power frequency operating voltage while an extremely uneven voltage distribution under trigger impulse can be achieved by proper parameter setting. The even voltage distribution enables the multi-gap spark switch to withstand much higher voltage than that in operation, thus avoiding false firing. On the contrary, extremely uneven voltage distribution could initiate cascade discharge at low amplitude impulse, insuring reliable triggering. The working principle of the new multi-gap spark switch differs considerably from that of the current spark gaps in H.V. and pulsed power systems. It has high reliability and no dead zone of trigger control, which can be sufficiently used as a high speed bypass switch for overvoltage protection applications in EHV grids. The conceptual design of the multi-spark gap switch, simulation of the frequency-dependent voltage distribution, cascade discharge of the spark gaps as well as the experimental performance verification on the prototype are presented in this paper.