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Voltage Regulation: Tapping Distributed Energy Resources

Voltage Regulation
Fortnightly Magazine - September 2004

receive an availability payment and an enabling payment when they are dispatched, and generators receive a compensation payment when they are restrained from operating according to market conditions. In France, EdF has found that distributed generators provide a powerful tool for regulating voltage and a concept of local controllers to manage the system in real time is being developed. Bonneville Power Administration is developing a new concept called "Energy Web," which includes local smart voltage regulation. As the causal factors of the Northeast blackout are more fully explored, the authors suspect that much greater emphasis will be placed on providing dynamic reactive power reserves, and that DER will play a large role in providing these reserves. Classifying the DER technologies as a regulated T&D resource could greatly hasten their development.

Endnotes

    1. P. Overholt, "Measurement Practices for Reliability and Power Quality, A Tool Kit of Reliability Measurement Practices," U.S. Department of Energy, www.ornl.gov/sci/btc/apps/Restructuring/pub.htm.

    2. M. W. Davis, "Distributed Resource Electric Power Systems Offer Significant Advantages over Central Station Generation and T&D Power Systems," IEEE Power Engineering Society Summer Meeting, 21-25 July 2002, pp. 54-69.

    3. G. Huang, H. Zhang, "Dynamic Voltage Stability Reserve Studies for Deregulated Environment," IEEE Power Engineering Summer Meeting, 15-19 July 2001, pp. 301-306.

    4. N. G. Hingorani, L. Gyugi, Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems, IEEE Press, 2000.

    5. C. W. Taylor, "Line Drop Compensation, High Side Voltage Control, Secondary Voltage Control - Why not Control a Generator Like a Static Var Compensator?", IEEE Power Engineering Summer Meeting, 16-20 July 2000, pp. 307-310.

    6. I. Kamwa, R. Grondin, Y. Hebert, "Wide-Area Measurement Based Stabilizing Control of Large Power Systems, A Decentralized/Hierarchical Approach," IEEE Transactions on Power Systems, vol. 16, no. 1, February 2001, pp. 136-153.

    7. J. Zhong, K. Bhattacharya, J. Daalder, "Reactive Power As An Ancillary Service: Issues in Optimal Procurement," IEEE International Conference on Power System Technology, 4-7 Dec 2000, pp. 885-890.

    8. Ibid., Huang and Zhang.

    DER Defined

    Distributed energy resources (DER) are small power sources such as microturbines, fuel cells or engine generators installed throughout the distribution system. An important role for these small power sources may be the supply of reactive power. Reactive power could be supplied dynamically, that is, it could be increased or decreased quickly. Reactive power could be used to regulate voltage at the distribution level. Reactive power supply currently is unevenly distributed and is typically available only in limited quantities in distribution systems. Having a dynamic supply of reactive power available from the distribution system would make the entire grid more efficient and reliable.

    Voltage Instability and Reactive Power

    Voltage instability is a growing concern in modern power systems. Restructuring of the power system has reduced voltage security margins for a number of reasons.

  1. To reduce capital investment cost, generation companies are buying generators with lower reactive support capability since they have a lower cost per megawatt;
  2. To minimize reactive power payments, system planners are relying more and more on capacitor banks instead of the more expensive dynamic reactive sources such as generators, synchronous