Countermeasures on preventing backup protection mal-operation during load flow transferring

Removal of transmission lines in power systems may result in load flow transferring and unreasonable operations of backup protections, which may develop into cascading tripping accidents and even blackouts. Traditional backup protection based on local measurement information has disadvantages in preventing from cascading trip because it cannot distinguish the over load reason between due to faults and due to load flow transferring. On the premise that the load flow transferring can be identified based on wide-area coordination system, concise adaptive adjustment methods for the operation characteristics of zone III distance protection and overcurrent protections are proposed to avoid the maloperation caused by load flow transferring. Meanwhile, their backup protection functionality can be reserve to a great extent. The simulation test results illustrate the validity of the proposed method. (C) 2015 Elsevier Ltd. All rights reserved.