This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON POWER SYSTEMS 1 Inertia Estimation of the GB Power System Using Synchrophasor Measurements Phillip M. Ashton, Student Member, IEEE, Christopher S. Saunders, Member, IEEE, Gareth A. Taylor, Senior Member, IEEE, Alex M. Carter, and Martin E. Bradley Abstract—A novel procedure for estimating the total inertia of the Great Britain (GB) power system is presented. Following an instantaneous in-feed loss, regional variations in the estimate of in- ertia are obtained from measured frequency transients using in- stalled synchronised phasor measurement units (PMUs). A method is proposed to first detect a suitable event for analysis, and then filter the measured transients in order to obtain a reliable estimate of inertia for a given region of the GB network. The total inertia for the whole system is then calculated as a summation, with an es- timate also provided as to the contribution to inertia from residual sources, namely synchronously connected demand and embedded generation. The approach is first demonstrated on the full dynamic model of the GB transmission system, before results are presented from analyzing the impact of a number of instantaneous transmis- sion in-feed loss events using phase-angle data provided by PMUs from the GB transmission network and also devices installed at the domestic supply at 4 GB universities. Index Terms—Frequency response, inertia, phasor measure- ment unit (PMU), power system dynamic stability, synchrophasor, wide area monitoring system (WAMS). I. INTRODUCTION I N line with the U.K. and European parliaments’ legislation on CO reduction, the generation pattern in Great Britain (GB) is rapidly evolving. The GB system is required to accom- modate an increasing volume of renewable energy, predomi- nantly in the form of offshore wind, asynchronously connecting to the periphery of the transmission system. This displacement of traditional thermal generation is leading to a significant re- duction in system inertia, thus making the task of system oper- ation more challenging. The inevitable shift towards a more dynamic system com- pounds the existing issues of calculating generator response and reserve requirements, which traditionally assume that system inertia varies linearly with demand. With demand being met by a growing percentage of asynchronous generation, such as renewables and HVDC interconnectors, this assumption is be- coming increasingly invalid. Frequency services are becoming more complicated and less predictable throughout the day, Manuscript received November 09, 2013; revised April 21, 2014; accepted June 17, 2014. Paper no. TPWRS-01442-2013. P. M. Ashton and G. A. Taylor are with Brunel University, London, U.K. C. S. Saunders is with Brunel University, Brunel Institute of Power Systems, Uxbridge, U.K. (e-mail: cssaunders@ieee.org; cssaunders@gmail.com). A. M. Carter and M. E. Bradley are with National Grid U.K., Wokingham, U.K. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPWRS.2014.2333776 forcing reassessment of generation patterns and limitations on single circuit risks, making it more difficult to maintain security for all credible contingencies. It is therefore necessary to gain an improved understanding of both the inertial frequency response of the power system and the security of the system in near to real-time. This will ensure the impact of incidents to specific areas of the network is un- derstood, facilitating more economically efficient operation of the power system. Importance is therefore placed on the pro- vision of time-synchronized frequency measurements that are now vital for this analysis. To that effect, the inclusion of phasor measurement units (PMUs) in the transmission system of England and Wales, with their high-resolution measurements and improved accuracy of data, is providing greater detail on the dynamic behavior of the power system in both real-time and during post-event analysis. With synchrophasor data made available at 50 Hz on the GB system, both transient and dynamic events occurring on the network are now captured. However, it has been shown [1] that the placement of a PMU with respect to a system event can greatly affect the post-fault frequency measurement and any corresponding analysis of that event. In addition, the stan- dard for synchrophasor measurements (IEEE C37.118.1-2011) leaves both the method of frequency measurement and the devices performance under transient conditions unspecified [2], meaning that under such conditions devices from different manufactures could produce widely varying results. In this paper a method is proposed for estimating the total inertia of the GB power system, by dividing the network into groups or regions of generation based around the constraint boundaries of the GB network [3]. The inertia is first estimated at a regional level before it is combined to provide a total esti- mate for the whole network. This estimate is then compared with the known contribution to inertia from generation, to provide an estimate for the currently unknown contribution to inertia from residual sources; namely synchronously connected demand and embedded generation. The approach is first demonstrated on the full dynamic model of the GB power system before results are presented from analyzing the impact of 22 instantaneous trans- mission in-feed loss events, using phase-angle data provided by 3 PMUs from the GB transmission network and also devices in- stalled at the domestic supply at 4 GB universities. The remainder of this paper is organised as follows. In Section II, the GB transmission system is described in addition to the existing and future frequency response requirements. In Section III, an overview is provided on the existing PMU deployment on the GB system. Section IV details the litera- ture-based methods of inertial frequency response estimation 0885-8950 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.