Chalamchi - Electric Power Research Center
Biglar - IRANIAN UNIV. of SCI.& fech
Rahbar - IRANIAN UNIV. of SCI.& fech

In this paper, a brief theoretical study of the interfrence in protection between power plant and power system has been presented.Study of the statistical diagrams and data regarding the number of malfunct- ions of generator,step up transformer and power plant substation protective relays on the basis of fault occurence out of' protective zone in respect to the kind of relays, and year of above phenomena has been done. The unacceptable trip numbers of Rey gas power plant untis due to fault occurance on the neighbouring transmission lines, and number of transformer trips followed by the above mentioned fault has been analysed. As conclusion, possible solution for reduction of the interfrence between Rey power plant and the neighbouring 230 Kv networks, and consequently production increase and availability of power plant units has been discussed.