Communication Delays in Wide Area Measurement Systems (WAMS) Biju Naduvathuparambil, Matthew C. Valenti, and Ali Feliachi Lane Department of Comp. Sci. & Elect. Eng. West Virginia University

Preview of Talk Idea: Communication delays in WAMS due to the usage of phasor measurement units (PMUs). Motivation: The use of innovative techniques like PMUs in wide area protection systems in a deregulated power industry. Technique: PMU processing time, PMU data format (IEEE 1344) length, and communication link involved.

Wide Area Protection  Technical Advantage:  Wide area protection (WAP) systems (with the help of Phasor Measurement Units) enhance system reliability by early detection and immediate avoidance of possible catastrophic events.  Economics:  WAP is an appropriate system for business support in an unbundled and open-access utility environment.  WAP is designed for an open-access market where production and transmission patterns will more often change than in a closed market.  WAP creates maximum profitability by reducing downtime and by optimizing system performance.

System Setup of WAMS

Phasor Measurement Units

PMU Facts PMU uses discrete Fourier transform (DFT) to obtain the fundamental frequency components of voltage / current. Data samples are taken over one cycle / multiple cycles. Currently, sampling is done at 12 samples/cycle (IEEE C Std.). Resolution of the A / D converter is 16 bits.

Technique behind PMU Samples are used to calculate the fundamental frequency component – phasor magnitude and phasor angle. X = phasor, N = total number of samples, x k = waveform sample The positive sequence phasor is then calculated as:

Applications of PMUs State estimation Instability prediction Adaptive relaying Improved control of power systems

PMU Data Communication PMU communicates using the IEEE 1344 data format. IEEE 1344 –Data frame Information regarding phasor data –Header frame Identification information about the PMU –Configuration frame Number of phasors and digital channels

IEEE 1344 Type of frame Nature of dataAverage length (bits) Data Frame Phasor information Channel digital input data Trigger status of frequency, angle, Over-current, under-voltage Rate of frequency change 640 Header Frame PMU identification code Data source information Algorithms and filter data 200 Configuration Frame PMU information Number of phasors and channels Nominal line frequency Transmission period of phasors 2800

Communication Options Telephone lines Fiber-optic cables Satellites Power lines Microwave links

Communication Delay Causes Transducer delays Window size of the DFT Processing time Data size of the PMU output Multiplexing and transitions Communication link involved Data concentrators

Delay Calculations The total delay can be expressed as: fixed delay link propagation delay L amount of data transmitted R data rate of the link associated random delay jitter

Delay Calculations…… Fixed delay –Delay due to processing, DFT, multiplexing and data concentration –Independent of communication medium used –Estimated to be around 75 ms Propagation delay –Function of the communication link and physical separation –Ranges from 25 ms in case of fiber-optic cables to 200 ms in case of low earth orbiting (LEO) satellites

Delay Calculations…… The data length L of the PMU message is assumed to be around 3640 bits (including data, header and configuration frames) The data rate R is assumed to be around 33.6 kbps for telephone lines and power lines. The data rate R, for fiber-optic cables and microwave links, is considered to be infinity for all practical purposes

Delay Calculation Table Communication link Associated delay – one way (milliseconds) Fiber-optic cables~ Microwave links~ Power line (PLC)~ Telephone lines~ Satellite link~

Conclusion Communication delays play an important role in determining the effectiveness of control procedures Delay parameters presented can be integrated with power systems design and analysis. –Distributed control with outdated measurements.