A Reactive Solution to Renewables’ Growth on the Grid

The post A Reactive Solution to Renewables' Growth on the Grid appeared first on POWER Magazine.

Electricity transmission network operators are being tasked with adding more renewable energy resources to the power grid. The use of static VAR compensators (SVCs) is growing as a means to control voltage fluctuations and improve power quality and efficiency.

The power grid continues to evolve, particularly as transmission system operators look to integrate more intermittent renewable resources into the electricity supply.

The use of static VAR compensators (VAR stands for volt-ampere reactive), known as SVCs, is growing as a means to suppress voltage fluctuations. SVCs provide dynamic voltage support, and help maintain the reliability and efficiency of the power supply. The technology is being integrated into both existing and new power infrastructure (Figure 1), helping reduce the investment that would be required to build new network extensions.

1. Static VAR compensators (SVCs) can be integrated into existing power infrastructure, such as at this substation. SVCs are a key component of facilitating the addition of renewable energy resources to the power grid, helping control voltage fluctuations. Courtesy: Siemens Energy

The importance of SVCs grows as more renewable energy resources come online, and more conventional power sources such as coal-fired and natural gas-fired generation are retired. Renewable resources lack any automatic frequency response mechanism, such as those found in large rotating thermal turbine-generators. SVCs mimic the action of rotating thermal turbines, and provide the ability to respond quickly, usually within milliseconds, to reactive power transients on high-voltage electrical transmission lines.

The technology includes a static synchronous compensator (STATCOM), or static synchronous condenser (STATCON), a regulating device used on alternating current (AC) electricity transmission networks. It is based on a power electronics voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If connected to a source of power, it can also provide active AC power. SVCs are part of the flexible AC transmission system (FACTS) device family.

In today's environment, thermal power plants are being decommissioned and replaced by wind and solar," said Fabrice Jullien, Global FACTS Business Leader for Grid Integration Solutions, in GE Renewable Energy's Grid Solutions business. Jullien told POWER, When this happens, the grid can become weaker'... meaning that it is not as stable and is prone to larger voltage swings based on changes in both generation and load. SVCs can be helpful in these scenarios to stabilize the voltage on the network."

Jullien said the SVC is a reactive power source that uses complex control systems and thyristor switches to dynamically control reactive power output," which he noted is measured in mega-VAR, or Mvar. SVCs can either generate or absorb reactive power, which helps maintain the voltage level on the local grid, thereby improving the stability and reliability."

Reactive Power Compensation

The differing types of technology that provide reactive power compensation include both the SVC and the STATCOM, said both Jullien and Dmitriy Anichkov, chief technology officer for Merit Controls and Merit SI, groups that provide power control systems and grid integration solutions for renewable energy installations. Anichkov told POWER, STATCOM is a power-electronics device typically used for reactive power control supporting electrical networks with a poor power factor or inadequate voltage regulation."

Anichkov said SVC has become an important technical means of overcoming the bottleneck of power transmission," and said that in his company's opinion, STATCOM has better operational characteristics than SVC."

Anichkov said, SVC and STATCOM are expensive since they are proprietary and unique. Replacing expensive proprietary SVC and STATCOMs with a single-cycle phasor-based control system and off-the-shelf inverters is a viable and appealing alternative. Modern grid benefits of a phasor-based control combined with inverters delivers full value stack optimization of energy storage," which he said includes the following benefits:

• Demand charge and energy cost reduction through real-time optimization of energy storage.

• Time-of-use (TOU) energy shifting.

• Power factor management within utility requirements, and voltage and frequency stability improvements.

• Seamless islanding and reconnection to a main grid with multiple distributed energy resources, such as solar and wind power.

Phasor-based control, in our opinion, should be applied wider, bringing above-mentioned and other benefits to the whole range of renewable generators such as wind, solar, and their hybrids with the battery storage," Anichkov said. Besides, phasor-based control should be used not only for distributed energy resources, small-scale power generation, or storage technologies typically in the range of 1 kW to 10,000 kW, but also for large utility-scale generating assets."

SVC Applications

There are many players in the global SVC market. Along with GE and Merit, they include well-known names such as Hitachi ABB Power Grids, Siemens Energy, Mitsubishi Electric, and S&C Electric. Other companies in the market include AMSC, Ingeteam, Comsys AB, and Merus Power.

Practical applications of SVC technology are in operation at several sites worldwide. VT Transco, Vermont's transmission utility, uses GE's technology; a 115-kV connected SVC from GE provides from +50 Mvar to -25 Mvar to VT Transco's network, improving reliability and voltage performance in the area.

Another large GE SVC is at Santa Barbara D'Oeste, Brazil (Figure 2). It operates at 440 kV and supplies +/-300 Mvar of power compensation at that site. The Power Grid Co. of India uses a GE SVC, operating at 500-kV, -500/0-Mvar system at a site in Kurukshetra, India.

2. The SVC technology from GE at this site in Santa Barbara D'Oeste, Brazil, operates at 440 kV and supplies +/-300 Mvar of power compensation. Courtesy: GE Renewable Energy

GE in July 2019 collaborated with Statnett, Norway's electrical transmission system operator, to upgrade existing SVC technology at the Rod and Verdal substations. At the time, Espen Bostadlokken, Norway country manager at GE Renewable Energy's Grid Solutions business, said, The upgrades to the Rod and Verdal substations will be the largest SVC revamp project Statnett has ever undertaken and one of the largest in the industry. Statnett's most recent contract with GE ensures a secure supply and improves the reliability and availability of the electrical transmission grid."

Jullien told POWER that while SVCs have been in service for years, STATCOM is a newer, but well-proven technology, which is based on a power electronics device known as an IGBT [insulated-gate bipolar transistor]." He said STATCOM and SVC both have their place depending on the particular customer problem that is trying to be solved.

SVC is a mature technology based on power electronics devices known as thyristors," Jullien said. Upgrades are somewhat limited on this mature technology, and are typically found in the thyristors themselves ... with improvements in voltage and current capability. One major improvement to SVCs was introduced by GE, and is referred to as GE's Main Reactor SVC. This technology is unique to GE as we have patented the core design attributes.

The Main Reactor SVC is different from traditional SVCs in that it improves harmonic performance [blocks harmonics from entering the grid], [and] has a smaller footprint and improved operational performance," Jullien said. GE has six Main Reactor SVC's operational, including our first project, which was completed in 2013."

Hitachi ABB Power Grids noted STATCOM is faster than SVC, and continuously provides variable reactive power in response to voltage variations, supporting the stability of the grid." The group on its website said, STATCOM operates according to voltage source converter [VSC] principles, combining unique PWM [pulse width modulation] with millisecond switching." It said STATCOM functions with a very limited need for harmonic filters, contributing to a small physical footprint. If required, switched or fixed air core reactors and capacitors can be used with the VSC as additional reactive power elements to achieve any desired range."

As for practical applications, Hitachi ABB said, Installing a STATCOM at one or more suitable points in a grid will increase power transfer capability by enhancing voltage stability and maintaining a smooth voltage profile under different network conditions. Its ability to perform active filtering is also very useful for improvements in power quality."

The high-power STATCOM market includes Hitachi ABB's SVC Light STATCOM, along with the PCS 6000 STATCOM, where PCS 6000 STATCOM is applicable for unit ratings up to 40 Mvar, and SVC Light STATCOM is applicable for ratings exceeding 40 Mvar. The group said that SVC Light is a VSC concept, based on a chain-link modular multilevel converter [MMC], particularly adapted for power system applications. Physically, SVC Light can be considered a voltage source behind a reactance. It generates and absorbs reactive power by electronically processing voltage and current waveforms in the VSC, rendering unnecessary to include physical capacitor and reactor branches for generating/absorbing reactive power. It is capable of yielding a high reactive power input to the grid more or less unimpeded by possible suppressed grid voltages, and with a high dynamic response."

The group said that technology can help support weak grids," and improve the performance of large wind farms under varying grid conditions, as well as of grids loaded by a large percentage of air conditioners in hot and humid climates."

Project Phoenix

Hitachi ABB is working with SP Energy Networks (SPEN) on a trial of a new hybrid synchronous compensator (HSC) in the UK. Project Phoenix, as the trial is known, involves monitoring the HSC over the next year at the Neilston substation, on SPEN's transmission network near Glasgow, Scotland. Other groups involved include National Grid ESO, the University of Strathclyde, and the Technical University of Denmark.

The groups said the compensators will provide dynamic voltage control, inertia, and short circuit level to help manage the reduction in synchronous generation from coal- and natural gas-fired power plants. The hybrid will combine synchronous condensers and static compensators.

SPEN said combining the rotating power source with the static, and the fast response time with the stable power supply, will enable the two technologies to complement each other. This will help provide services such as inertia that are being lost as the UK transitions away from fossil fuel-powered generation to the use of more renewable energy resources.

The Project Phoenix trial will provide data that will be collected and analyzed, with the goal of proving the hybrid concept and subsequently validating its commercial application. SPEN has said the project will increase grid stability, even as more renewable resources come online, and reduce network operating costs by between 53 million ($70 million) and 66 million ($87 million).

-Darrell Proctor is associate editor for POWER (@POWERmagazine).

The post A Reactive Solution to Renewables' Growth on the Grid appeared first on POWER Magazine.