Alternative approaches and dynamic analysis considerations for detecting open phase conductors in three phase power systems

Abstract

Open phase conductors in three-phase power systems can be difficult to detect with conventional protection relay schemes. Such events can have adverse consequences to power system equipment reliability and performance. The resultant voltage unbalance associated with open phase events can cause excessive heating in transformer core and coil assemblies and tanks, reduce the available starting and running torque of motors, increase motor acceleration time, cause inadvertent tripping of critical loads, and thermally damage plant equipment.Power system response to an open phase condition is highly dependent on a number of factors, including the type of open phase condition (events involving one or two phase conductors, coupled with or without a ground), the location of the open phase, the topology of the power system, transformer core design and winding connections, and type and magnitude of system loading.This paper briefly describes industry operating experience with open phase events. It summarizes the various alternative approaches for detecting open phase conductors on large station service transformers. Dynamic modeling considerations and techniques are described and a summary of analytical results which convey the challenges, advantages, and disadvantages associated with different detection strategies are presented. The role symmetrical components and sequence components can play in understanding the impact of open phase conditions on power system equipment also is discussed.