Using Dynamic VAR Technologies to Boost Grid Reliability

By John B. Howe, American Superconductor


Today’s competitive pressures and siting obstacles make sound planning for transmission system expansion more important-yet more uncertain-than ever before. To manage these challenges cost-effectively, new tools are required. Recent material advances have resulted in a new generation of distributed, dynamic reactive power technologies to improve grid reliability and capacity. Modular and scalable, they enable a flexible “just-in-time” approach by which planners and operators can achieve reliability targets and limit financial risk in the face of the constantly evolving uncertainties inherent in an open, competitive supply market.

Challenges and Uncertainties Facing the Grid

In recent years, rising burdens on our nation’s aging power grids have caused widespread congestion and reliability problems. The high cost of years of shortchanged grid investment is now evident. Today’s grid planners and operators require new tools and strategies that restore network flexibility while meeting today’s land use and environmental concerns. Our technology-intensive economy depends on electricity, which has powered more than 85 percent of our nation’s economic growth since 1980 and supplies more than 40 percent of today’s end-use energy consumption. Far from diminishing in importance as some industry pundits forecasted in the 1990s, the high-voltage transmission grid has emerged as the indispensable energy infrastructure of the 21st century.

Based on current trends in generation, our need for a secure, high-capacity, stable and flexible grid will only grow in the future. As North American natural gas supplies dwindle and concerns mount about the national security and balance-of-payments impacts of high levels of energy imports, industry leaders are calling for a larger role for domestic coal, nuclear and renewable energies. These resources, while abundant, share an important attribute: They are found, or must be sited, in areas remote from metropolitan load centers and will require major grid reinforcement to reach markets.

But what about siting? Despite broad agreement in principle on the need for grid expansion, gaining support “on the ground” from local communities to implement actual grid upgrades remains one of the toughest challenges facing today’s utilities. Siting new high-voltage lines is especially difficult in and around the metropolitan areas where much of today’s economic growth is concentrated.

A solution to this dilemma must be found. At stake is the realization of the Congressional goal, set forth in the Energy Policy Act of 1992, of robust, open and non-discriminatory wholesale electricity markets. Efforts by the Federal Energy Regulatory Commission (FERC) to implement this vision have hit many roadblocks. It has proven difficult to develop fair, non-discriminatory processes to integrate the “queue” of large numbers of proposed generators whose effects on power flows are highly interactive, and whose timing is highly uncertain. Sharp volatility in fuels markets has disrupted the economics and predictability of generator dispatch. Globalization has driven sudden shifts in patterns of industrial activity and electrical load. Rising surpluses have pressured some grid operators to retire older, dirtier urban generators that support voltage inside hard-to-serve load pockets. A recent study by Energy Security Analysis Inc. (ESAI) described operator interventions to delay or prevent the retirement of these high-cost plants as “one more piece of friction that prevents the electricity market from behaving like ordinary markets.”

All of these factors beg the question: How can grid reliability be maintained, without the construction of costly, controversial and possibly redundant facilities, when basic grid topology is subject to so many uncertainties?

In Physics We Trust: The Renewed Focus on Reactive Power

The key to achieving this goal lies in a renewed focus on the basic physics of electricity. After years of declining system margins, mounting complexities and a spate of costly blackouts, industry leaders and policymakers are re-examining the link between reactive power management practices and grid reliability. The reason is simple. Within a regulated monopoly structure or an open, competitive environment, grid operators face the same imperative: to maintain near-constant frequency and voltage, or electrical “pressure,” at all points across the grid and through all moments in time, for a non-storable product-or else risk sudden and severe consequences.

Other networks take advantage of forgiving physical characteristics to maintain reliability. For example, gas pipelines have “linepack” storage; long-distance telecom networks have massive redundancy; and local telecom networks can employ a “fast busy” signal to avoid overloads. Operators of AC power networks, however, must closely and continuously balance real power (megawatt) and reactive power (volt-ampere reactive, or VAR) flows. Unfortunately, VARs “don’t travel well” and must be supplied close to load centers. Moreover, VAR support needs have grown with the steady spread of air conditioning and other types of inductive motor loads. Political desires to move generation away from populated areas must be balanced with the physical need to maintain local voltage support with sources of fast-acting, dynamic VARs to counter random grid disturbances. Where VAR support is inadequate, grids must be operated with heightened caution; many lines are rated well below their full thermal capacity because when grids are stressed, even brief voltage drops caused by transient events (e.g., line outages, plant trips, lightning strikes) can trigger instability and collapse.

Why is this issue coming to the fore now? Initially in the 1990s, electricity restructuring debates focused on the development of markets for real power because, as Willie Sutton would say, that’s where the money is-or was. Reactive power management, an arcane topic addressed internally by yesterday’s integrated utilities, largely slipped through the cracks. No longer is this the case. Especially after the massive and costly Northeast blackout of August 2003, VAR management is receiving high-level attention on many fronts:

“-The Final Report of the U.S.-Canada Blackout Task Force found that inadequate management of reactive power and voltage was among the principal causes of that event.

“-In its February 2004 response to the blackout, the North American Electric Reliability Council (NERC) issued guidance to grid operators urging re-evaluation of their reactive power and voltage control practices.

“-New NERC standards that went into effect in April 2005 establish, for the first time, clear responsibility for reactive power planning in today’s unbundled environment.

“-These industry-led standards could soon have the bite of federal enforcement authority under pending national energy legislation.

“-FERC staff issued a report on reactive power supply and consumption in February 2005 that outlines a range of new pricing and policy approaches to better ensure that reactive power needs are met cost-effectively.

Dedicated, Dynamic, Distributed: The Emergence of New VAR Technologies

Meeting the reactive power requirements of today’s system is more than a matter of setting clear, enforceable standards, pricing reforms and other policy initiatives. Ultimately, new technology solutions are the key to achieving proper VAR management within a competitive market framework and with the least siting and environmental impact. New materials developed within the past few decades, including power semiconductors and superconductors, have led to a range of new technology tools that are well suited to this challenge. These devices operate by enabling the instantaneous injection of VARs, at dispersed and optimized locations on the grid, to dampen out voltage disturbances. This capability, in turn, allows higher loadings on existing, stability-constrained lines. These new technologies combine high performance and cost-effectiveness with minimal siting impacts, speedy installation and, in many cases, mobility. Some examples include the following:

FACTS: Broadly speaking, the concepts underlying Flexible AC Transmission System (FACTS) technology originated in the early 1970s with the development of high-power thyristors or power semiconductor chips. The first FACTS devices entered service in the late 1980s, and, today, a wide range of FACTS technologies are in use around the world.

D-VAR: Further advances in power electronics have resulted in a new generation of modular FACTS devices with even greater power density and responsiveness that are being used in applications previously dominated by Static VAR Compensators (SVC). The D-VAR (Dynamic Volt-Ampere Reactive) voltage regulation system is a FACTS device that employs Insulated Gate Bipolar Transistor (IGBT) based inverters and, in some applications, superconducting magnetic energy storage (SMES) to inject leading or lagging voltage precisely where it is needed in a grid. D-VAR systems can be customized to meet specific customer needs and changing grid conditions through variations in operating software and in the number of inverters required for the proper level of VAR support. Employed in U.S. grids since 2000, compact D-VAR systems can be packaged in mobile, redeployable trailers or installed permanently within substations. A larger, centralized version of the D-VAR is called the Dynamic VAR Compensator (DVC) system.


D-VAR solution at a wind farm in the Orkney Island region of Scotland. This recent project was installed inside a permanent building for protection from the harsh ocean air environment. Click here to enlarge image

Several dozen D-VAR systems are now in use on utility grids throughout the United States, Canada and in Great Britain to enhance power transfers into, across and out of congested areas while improving grid reliability and power quality. The D-VAR solution can be used to reduce or eliminate operation of costly “reliability must run” generation, to mitigate local generation market power, and to minimize the need to invoke under-voltage load shedding-traditionally the operator’s reliability tool of last resort. Many D-VAR systems also operate at the grid interfaces of wind farms, where wind gusts can result in acute voltage management issues.

SuperVAR: Advances in the field of high-temperature superconductor (HTS) wires are further expanding the range of dynamic VAR solutions. The SuperVAR dynamic synchronous condenser is a new application that helps to stabilize grid voltage, increase service reliability and maximize transmission capacity by acting as a “shock absorber” for grid voltage fluctuations. The first SuperVAR prototype is currently undergoing evaluation in an application to mitigate flicker caused by an arc furnace at a steel mill on the Tennessee Valley Authority (TVA) grid. Adapted from designs for ultracompact HTS ship propulsion motors, the SuperVAR employs a standard set of stator coils married with power-dense HTS rotor coils. This package is able to supply large amounts of reactive power support very efficiently and can operate at several times its nominal rating for short periods to dampen out more severe transient disturbances. Within the next year, SuperVAR will become the first utility-scale application of revolutionary HTS wire technology to reach full commercialization.

A “Just-In-Time” Grid: Using Dynamic VARs to Narrow Planning Uncertainty

Many of the difficulties facing grid operators arise from the need to maintain reliability in real-time with facilities planned many years in advance on the basis of uncertain forecasts. Today’s dynamic VAR technologies offer new ways to reduce this risk of forecast uncertainty. Modular and compact, they are easily studied, sited and installed within a single annual planning cycle. The ability to install pad-mounted equipment, or to place it in standard containers or mobile trailers, enables these assets to be relocated as system needs change-minimizing exposure to stranded investment. Modular design allows flexible, large-scale solutions based on multiple units to be placed at diverse locations on the grid. This distributed approach has been shown to provide more effective-and cost-effective-protection against random grid disturbances caused by plant trips, lightning strikes and other events whose location cannot be pinpointed in advance.

Today’s high-performance dynamic VAR technologies, in short, offer a flexible “just-in-time” approach to grid planning. As never before, transmission networks can be “tuned” to meet voltage stability challenges resulting from deviations from the long-term plan, whether those deviations are caused by generator additions and retirements, load growth, delays in planned line construction and upgrades, or other changes in topology. Modular dynamic VAR systems can be installed on a permanent or relocatable basis as best meets system needs. This approach can help operators maintain reliability in real-time while planners defer costly and irreversible commitments to major grid resources (e.g., larger generators, overhead high-voltage lines) until it is clear they are needed. In turn, as these resources are operational, mobile dynamic VAR resources can be freed-up and redeployed to other locations at low incremental cost, further leveraging their value.

Helping Competitive Markets Flourish

The long period of regulatory uncertainty and investment paralysis that has gripped the electric transmission sector has proven costly to the nation’s economy and to the industry’s confidence-both in itself and in the Congress’s vision of a robust, competitive electricity marketplace. In recent months, some skeptics have voiced doubts that a truly competitive electricity marketplace is even achievable, at least along FERC’s current pathway. The American Public Power Association, the Progress and Freedom Foundation, Cato Institute, and ELCON (Electricity Consumers Resource Council) have all issued position papers questioning the basic direction of competitive market reforms under FERC’s framework of open access and institutionalized regional markets.


Interior view of the climate-controlled building that houses the Orkney Island D-VAR solution. Click here to enlarge image

The political debate over restructuring is certain to continue. Opponents of restructuring will challenge the basic logic of competition and reliance on market forces. Meanwhile, pro-market defenders will point to successes elsewhere and focus on deficiencies in the market model implemented thus far in the United States. But the best pathway forward is to adopt rules and implement technology solutions that reflect the unique physical realities of electric power networks.

In this regard, the recent upsurge in policy attention to reactive power issues is an important and welcome development. Today’s dynamic VAR technologies-dedicated, dynamic and distributed-target the real need for voltage support that is cost-effective, fast-acting and that can be located precisely where it is most urgently needed. The “just-in-time” planning capability offered by these technologies gives grid operators the flexibility they need to better manage long-term capital expenditures, maintain reliability and master key planning uncertainties so that long-envisioned competitive markets may finally flourish.௣à¯£

John B. Howe is vice president of electric industry affairs for American Superconductor Corp. For more information, visit www.amsuper.com.

Author

  • The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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