New technology for Ameren Transmission: advanced voltage control for the grid

Ameren Transmission has activated the first two of four innovative upgrades to ensure the stability of its grid as the utility shifts to clean energy sources. Known as Static Synchronous Compensator (STATCOM), the technology helps ensure customers have safe, reliable and affordable power as fossil fuel hubs retire in Ameren’s service territory.

Fossil power centers, in addition to generating megawatts, also provide reactive power capabilities through generator excitation systems, thereby controlling the voltage of the transmission system in both steady state and transient conditions. As these plants retire, in addition to losing megawatt output, we also lose control of the voltage they supply, which could lead to system stability issues and a violation of NERC standards. . Due to Ameren’s commitment to clean energy and achieving zero net carbon emissions by 2050, Ameren Transmission has started planning for the withdrawal of several energy centers in Ameren’s service territory.

Transient conditions known as Fault Induced Delayed Voltage Recovery (FIDVR) events can cause network instability and loss of customer load. By performing a system simulation of the FIDVR events along with other transmission system planning studies, the team of planning engineers working with design engineering identified four locations in Ameren’s network that would require transient voltage control devices to operate stably and reliably. after the planned withdrawal of some coal-fired energy centers.

A team of planning, design, project management, construction and maintenance engineers was formed to develop a specification for the necessary voltage control devices taking into account steady state and transient performance, cost initial, operating and maintenance costs, safety and service life. long-term sustainability of the technology. Several types of solutions have been considered, in particular synchronous condensers, traditional static var compensation systems (SVC) and STATCOMs.

After reviewing several vendor solutions and proposals, the team decided that the STATCOM solution best met the requirements of the specification, providing significant performance advantages over SVC and synchronous capacitors in terms of increased reactive power capacity in transient conditions of low and high voltage, speed of response and reliability. The STATCOM design, based on a voltage source converter and Bipolar Insulated Gate Transistor (IGBT) power electronics, has provided the latest technology based on industry standard power electronics, providing a long-term durability, simpler design in terms of system integration (reduced harmonics) and lowest operating and maintenance costs.

A STATCOM installation has a relatively small footprint, requiring an area of ​​250 ft x 250 ft for a 250 Mvar installation. The STATCOM installation is illustrated in Fig. 1 with the design layout and a line.

Figure 1. Footprint of the STATCOM site, currently in the final construction phase before testing and commissioning.

The power and control modules (highlighted in yellow in Figure 1 a row) are located inside the building and constitute the basic building block of STATCOM. The stacks of power modules shown schematically in Figure 2 are composed of direct current capacitors and four IGBT switches per module. The power modules keep the load on the DC capacitors, which are then turned on and off to increase or decrease the voltage to inject current through a series reactor. The net effect is the positive or negative reactive power injected into the transmission grid to regulate the grid voltage.

Figure 2. Power module stack diagram and theory of operation.Figure 2. Power module stack diagram and theory of operation.

The first two of four STATCOM facilities are located near Wood River and Peoria, Illinois. These two sites provide advanced voltage control to Ameren customers affected by the decommissioning of large power plants in each region. These specific applications of STATCOM and future applications of the technology are also essential for the state of Illinois’ transition to a carbon neutral economy and for achieving its goal of 100% clean energy by 2050.

The Wood River area STATCOM provides transient voltage recovery to a highly industrialized corridor, which has a high energy demand and requires stable voltage on the system to ensure that manufacturing facilities remain online during these heavy events. ’emergency. After the installation of the Wood River area STATCOM in 2019, it has proven to meet high performance standards. An example of STATCOM performance from the Wood River region is shown in Fig. 3 for a nearby 138 kV line-to-earth fault.

Figure 3. STATCOM performance following a transmission short circuit condition.Figure 3. STATCOM performance following a transmission short circuit condition.

The above graph of the event showed that STATCOM was injecting reactive power, limiting voltage sag to less than 4% and returning the voltage to its pre-event state within 2 seconds. Ameren compared the voltage drop before and after installing STATCOM using system simulations. Without STATCOM, the voltage of 138 kV in the area would have dropped to around 90% of the nominal voltage over a long period of time. With STATCOM, the voltage of 138 kV was slightly above 96% of the nominal voltage during the disruption of the system, which would have exceeded the performance of the system before the production withdrawals in the region.

The second two of the four STATCOM facilities are located in Dupo, Illinois, and in the southern part of St. Louis County, Missouri. These STATCOMs provide transmission medium and voltage control in areas affected by the Meramec Energy Center withdrawal from Ameren located in St. Louis County along the Mississippi River. St. Louis County STATCOM is also part of the Missouri Smart Energy Plan, a multi-year plan that includes more than 2,000 projects to modernize energy infrastructure to support a cleaner, stronger energy grid.

STATCOM technology will be an integral part of Ameren’s goal of achieving net zero carbon emissions by 2050. In addition to retiring its fossil fuel hubs, Ameren is planning its largest expansion of clean wind and solar generation, while maintaining the reliability and affordability that customers expect.

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