With the developments of substation automation and local installation of controldevices, the electromagnetic environments of substation become more severe than before.First, the typical feature and coupling channel of disturbance source are considered. Andthen, the prominent problems about uncorrectable action of protective relays fordisturbance are discussed. Furthermore, in order to solve surge problem, the variousearthing modes of system earth in protection devices are analyzed. And some usefulconclusions had been got through the experimentations with CSL-101B and CSC-163,typical UHV transmission line protections. In the end, according to the limitation ofcentral power supply system, the distributed power supply system was put forward,and its effect had also been proved by experimentations.
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