Indian Experience on Impact of Leap Second in Synchrophasor Systems

Synchrophasor data is highly dependent on Global Positioning System (GPS) for its synchronized measurement as well as correct time stamping. Synchronized Time stamping is crucial when power system parameters of two or more locations are being correlated / calculated. Angular separation between any two locations of electric grid indicates the stress of the grid and is generally calculated from the phase angles measured by Phasor Measurement Units (PMU). Any time errors among these location PMUs results wide variations in angular difference pairs and may mislead the operator. In general PMU internal clock is always synchronized with GPS time, in case of time synchronization loss or drift with GPS time PMU flags the data as invalid. But during time discontinuities like leap second addition/deletion it does not flag the out-of-sync alarms. Hence, any improper handling of leap second event may distort the measurement presented to the power system operator, which may be detrimental to the power grid operation & control. This paper presents practical experiences of leap second events in Indian WAMS implemented under different pilot projects and discusses the issues associated with last three leap second events occurred on 30th June'12, 30th June'15 and 31th Dec'16. The paper also presents identification of leap second occurrence by power system operators through data and its handling by PMUs.