Performance of phasor measurement units for wide area real-time control

Phasor measurement units (PMU) are becoming a basic building block of modern wide area power system protection, monitoring and control schemes. Such systems rely on accurate time synchronized measurements. PMU operation is governed by the IEEE C37.118 standard. The standard sets out the performance requirements for valid phasor measurements under steady state conditions, but does not specify the response of PMUs under transient system conditions. Since most events requiring action by protection and control systems arise from transients it is important that PMUs report these anomalies in an understood and universal manner. This paper discusses the problem of determining phase during a transition from one cyclic state to another.