Abstract: The 35kV direct - current distribution technigue is an item popularized by CNPC. But there are partial breakdowns, which have caused rapid decline in the bus voltage of substations (the remaining voltage was too low). These problems should have been discovered after electric network was put into operation in Henan oilfield in 1989. Lots of oil raising engines have stopped because of release of alternating current contactor, too, there have been serious problems in relay protection. The stability of supply network and the output of crude oil have been impired by above defects. This article analyses these problems, takes reliable measures, such as increasing and seting up a limited current reactor, etc, and acheived tangible result.