Phasor measurement applications in smart grid

In Power systems, high voltage transmission and distribution lines are vital links to achieve the reliability of service to the end users. Today, the bulk power system is designed to meet customer demand in real time meaning supply and demand must be constantly and precisely balanced. As electricity cannot be presently stored on a large scale, changes in customer demand throughout the day and over the seasons are met by controlling conventional generation, using stored fuels to generate electricity when needed. Even with global climate change initiatives and the potential for changes in fuel mix and technologies, this continuous balancing of resources and demand will be required to maintain the reliability of the bulk power system. A significant challenge is to reliably integrate smart grid technologies while maintaining reliability.

Phasor data and applications are valuable for grid reliability because they give grid operators and planners unprecedented insight into what is happening on the grid at high resolution, over a wide area. in time synchronized mode, and where needed, in real-time. Synchro phasor systems allow the co1lection and sharing of high-speed, real-time, time-synchronized grid condition data across an entire system or interconnection. These data can be used to create wide-area visibility across the bulk power system in ways that let grid operators understand real-time conditions, S86 early evidence of emerging grid problems, and better diagnose, implement and evaluate remedial actions to protect system reliability.

Electricity growth in fast growing economy like India needs to match the pace of economic growth for sustained developmental efforts. Peak demand is expected to increase more than 157 GW by 2012 which requires installed capacity of about 210 GW as against present installed capacity of 167 GW. Further, to meet the growth rate of Indian Economy, installed capacity of Power Generation shall be about 600 GW by 2025. The distinct feature of power system development after Independence has been continuous growth of Interconnections giving rise to complex and integrated Electric Power Systems in States, Regions and Country as a whole. In recent past, there have been a number of initiatives taken to improve the Power System monitoring by implementing IT enabled tools. In this paper, the Voltage and Cummt Phasor measurements using Phasor Measurment Units and monitoring of Power Systems by applications of these phasor quantities is given.

Synchro-phasors are useful in improved visibility of Power System by observing System Voltage, Current, Fault Current and rate of change of frequency. PMU based measurements are required for preemptive control of any evolving abnormality in the Grid. Transmission Une capacity utilization can be optimized leading to cost optimization and enhanced efficiency of Transmission Networlc. PMU based Wide Area Monitoring System (WAMS) is like neural view of Power system. A synchronized phasor measurement provides the real possibility ofproviding a dynamic state estimator. Mostly Transmission Un. capability is limited by stability and not by thermal capacity. Synchro-phasors enable Grid operators to raise the stability limit by increasing the line load-ability and leading to better congestion management. In addition, PMU's are being used for applications such as On Line Computation of Transmission line Parameters, Differential Protection of Transmission line, Zone-3 Protection Blocking, Detection of Permamnent or Transient Faults in the Une using PMU based differential relays, Fault Location in Transmission Unes etc. and these have been described in this paper. Use of PMU's in other applications such as Low Frequency Oscillation Monitoring and Detection and Model validation, Transient Stability Monitoring are under development. The protective relay performance can also be monitored by monitoring variations in the Voltage and Current waveforms.

Measured voltages from PMU's can also be used for calibration of Capacitive Voltage Transformers and Current Transformers. As there are issues with the performance of CVTs in Indian Power Networlc and there have been many cases of CVT being out of Calibration after failures of Capacitor Elements, use of PMUs for real time calibrations of Capacitive Voltage Transformers by comparing output of precalibrated Potential transformer with other Capacitive Voltage Transformers/Voltage Transformers is being considered. This can be very useful for taking corrective and preventive actions.