Communication Delays in Wide Area Measurement Systems (WAMS)

1. 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

2. 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.

3. 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.

4. System Setup of WAMS

5. Phasor Measurement Units

6. 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 C37.111 Std.). • Resolution of the A / D converter is 16 bits.

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

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

9. 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

10. IEEE 1344

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

12. 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

13. 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

14. 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

15. 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

16. Delay Calculation Table

17. 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.