Scheme for accelerated trip for faults in the second zone of protection of a transmission line

A principle of trip acceleration which reaches to the end of the protected line in a multizone impedance protection is described. An impedance unit with zero sequence current as the polarization value which meets performance requirements against over-reach onto the next transmission line, has been developed. The difficult case where the next transmission line is short is discussed. Test results with a prototype device on a dynamic power system model verify the proposed principle. An operational prototype which has been installed on a 110 kV, 60 km transmission line is described.<
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