GPS and IEEE 1588 synchronization for the measurement of synchrophasors in electric power systems Andrea Carta, Nicola Locci, Carlo Muscas ⁎, Fabio Pinna, Sara Sulis University of Cagliari, Department of Electrical and Electronic Engineering, Piazza d'armi s.n., 09123 Cagliari, Italy abstract article info Available online 1 July 2010 Keywords: Synchrophasors Phasor Measurement Unit GPS IEEE 1588 Distributed measurement systems In modern transmission and distribution networks, monitoring, control and protection tasks are usually performed by Intelligent Electronic Devices (IEDs), that are often connected to each other by suitable communication links. Many of the procedures implemented require that the acquired data have an extremely accurate common time reference, with typical synchronization specifications ranging from milliseconds to a few hundreds of nanoseconds, according to the different use foreseen for the measured data. The strictest synchronization requirements lead to the need of highly accurate clock settings, such as the ones bases on satellite systems (e.g. the Global Positioning System, GPS). As an alternative, in situations where many devices are located in a geographically limited sub-area of the system, it could be advantageous to distribute the time reference to the remote stations through suitable network synchronization protocols. Between them, the PTP (Precision Time Protocol) defined in the Standard IEEE 1588 offers the best accuracy. This possibility is investigated in this paper, with special reference to one of the most challenging measurement problems, that is represented by the measurement of synchrophasors. Experimental results will be provided to evaluate the performance achievable with this solution. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Economical, political and social requirements push a continuous technological evolution in modern electric power systems. As an example, the diffusion of “Distributed Generation” (DG), i.e. small production plants, often supplied through renewable energy sources, gives rise to significant transformations in electric distribution systems. Indeed, the presence of DG has implications on both energy management (since “active networks” are needed to take into account bidirectional energy flows by means of innovative devices [1]) and protection systems (since adaptive protections can be used to automat- ically reconfigure the network in the case of fault occurrence [2]). In addition, the liberalized energy market makes more and more important to assess the responsibility of power quality disturbances among the different subjects. In the last years opportune parameters, frequently based on distributed and simultaneous measurements [3], have been proposed as a possible metric to characterize the quality of the service provided by System Operators. In general, in both transmission and distribution networks, moni- toring, control and protection tasks are usually performed by Intelligent Electronic Devices (IEDs). From an operative point of view, in this field it should be also taken into account the strong impact of the recent standards of the IEC 61850 series. These standards refer specifically to communication networks and systems in electric substations, but they are now taken as a de facto reference in all those circumstances where an electric system is managed with the help of inter-communicant IEDs (e.g. active networks for DG management, smart grids, etc.). In this way, control and protection schemes practically become algorithms, whose correct behavior is determined firstly by the avail- ability of data measured in strategic points of the network. The critical role of the above mentioned applications, which clearly emerges from their implications on safety, as well as from economical considerations, makes it of fundamental importance the evaluation of correctness and trustworthiness of the information on which such actions are based. Given that in many applications it is required that measurement, control and protection devices act in a strictly synchronized way, this paper focuses on the aspects related to the synchronization between IEDs. Synchronization requirements vary according to the tasks such devices should perform, ranging from milliseconds, for breaker operations and event reconstruction [4], to microseconds, for synchrophasor measurements [5–9], to a few hundreds of nanose- conds, for fault detection [4,10]. The tightest synchronization requirements lead to the need of highly accurate clock settings, that can be accomplished by means of GPS satellite systems. On the other hand, equipping each measure- ment station with a dedicated GPS receiver can be an optimal solution from a technical perspective, but can be impractical from the economic point of view. Therefore, the study of possible alternative Computer Standards & Interfaces 33 (2011) 176–181 ⁎ Corresponding author. Tel.: +39 070 6755860; fax: +39 070 6755900. E-mail address: carlo@diee.unica.it (C. Muscas). 0920-5489/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.csi.2010.06.009 Contents lists available at ScienceDirect Computer Standards & Interfaces journal homepage: www.elsevier.com/locate/csi