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

• The load flow transferring incident criterion is proposed in this paper.
• The circle operation features is adjusted to a lens-shaped feature.
• The inverse-time operating characteristic is adjusted to avoid the malfunction.
• Longer operating time for operation of emergency control devices can be obtained.

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 mal-operation 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.