Synchrophasors : De fi nition , Measurement , and Application

The concept of using phasors to describe power system operating quantities dates back to 1893 and Charles Proteus Steinmetz’s paper on mathematical techniques for analyzing AC networks. More recently, Steinmetz’s technique of phasor calculation has evolved into the calculation of real time phasor measurements that are synchronized to an absolute time reference. Although phasors have been clearly understood for over 100 years, the detailed definition of a time synchronized phasor has only recently been codified in the IEEE 1344 and the soon to be voted IEEE C37.118 Synchrophasor for Power Systems standards. This paper will review the concept of a phasor and examine the proposed IEEE standard as to “how” a synchronized phasor is to be defined, time stamped, and communicated. The paper will then examine the issues of implementing such measurements in the face of off-nominal frequency components, timing errors, sensor errors, and system harmonics. Simulations of various system transients and their phasor response will be presented. Finally, this paper will review the application of synchrophasors to observe power system dynamic phenomenon and how they will be used in the real-time control of the power system. Examples of system disturbances will be presented. Introduction As the electric power grid continues to expand and as transmission lines are pushed to their operating limits, the dynamic operation of the power system has become more of a concern and has become more difficult to accurately model. In addition, the ability to effect real-time system control is developing into a need in order to prevent wide scale cascading outages. For decades, control centers have estimated the “state” of the power system (the positive sequence voltage and angle at each network node) from measurements of the power flows through the power grid. It is very desirable to be able to “measure” the system state directly and/or augment existing estimators with additional information. Alternating Current (AC) quantities have been analyzed for over 100 years using a construct developed by Charles Proteus Steinmetz in 1893 know as a phasor. On the power system, phasors were used for analyzing AC quantities assuming a constant frequency. A relatively new variant of this technique that synchronizes the calculation of a phasor to absolute time has been developed, which is known as synchronized phasor measurement or synchrophasors. In order to uniformly create and disseminate these synchronized measurements, several aspects of phasor creation had to be codified. The following text spells out the definitions and requirements that have been established for the creation of synchronized phasor measurements. Synchrophasor Definition An AC waveform can be mathematically represented by the equation: