Synchronous Condensers: A New Trend in the Face of Power Plant Shutdowns

According to, 29 power plants have shut down worldwide in the last three years. This trend continues today, and with these power plant shutdowns, the focus is now on renewable energy to replace them. However, wind farms and solar fields cannot handle the reactive power demand from heavy industrial plants, so synchronous condensers have come to their rescue.

While synchronous condensers have been widely available for many years, they remain underappreciated and mostly unknown by the general public. With the power plant shutdowns, the rise and consistent implementation of synchronous condensers are a recent trend that is here to stay.

What is a Synchronous Condenser?

A Synchronous Condenser is a conventional 3600 rpm generator tied to a transmission system, but it doesn’t have a turbine inside the plant driving the generator. A Static Frequency Converter (SFC) is used to bring the generator up to 3600 rpm by applying power and causing the generator rotor to turn. The SFC brings the generator rotor up to 3610 rpm and then shuts off, which allows the generator rotor to start coasting down.

The automatic synchronizer will close the generator circuit breaker when the voltage, frequency, and phase angle between the generator and the grid are matched. At that point, the generator stator draws power in from the grid to keep the generator rotor turning at synchronous speed. The generator acts as a motor, and the amount of reactive power (MVARs) it produces can be varied just like any other turbine-driven generator.

The value of synchronous condensers has risen accordingly as renewable power grows. They provide voltage support and transmission line stability, especially in remote areas, but also where there are industrial plants that require a lot more power.

For example, there is a coal-fired power plant in Gary, Indiana, that is retiring. That is a heavy industrial area that needs voltage support. While it would appear that a utility could bring the needed reactive power in over transmission lines, the lines lose voltage the further it is transmitted, so it isn’t a viable option.

In that and other similar scenarios, synchronous condensers are needed to provide the voltage support industrial plants require because of their high-power usage. That voltage support is provided in the form of VARs and is measured in volt-amperes.

Critical Need for Infrastructure

This critical need for VARs to power industrial plants and their induction motors has continued to rise throughout the country as more power plants are scheduled to be shut down. In anticipation of this need for infrastructure that can replace the reactive power these plants supplied, synchronous condensers are currently being built in Gary and Valparaiso, Indiana.

Synchronous condensers are an old technology, but in today’s renewable energy environment, they have become increasingly more important. It isn’t often that something old becomes a crucial part of emerging technology. It leads to a frequently asked question—why isn’t standard renewable energy (wind, solar, battery, etc.) able to fill in and supply reactive energy in place of these power plants?

The answer is that renewables produce kilowatts, and they are limited in their ability to produce VARs. As more renewables are added to the electric grid and fewer coal-fired power plants, there is about a 90 percent shortage of the VARs needed for large industrial plants that wind and solar cannot produce.

This need to produce greater reactive power for industrial plants without coal-fired power plants has emerged in the last five years.

Building a Synchronous Condenser

From start to finish, or what we call commissioning, it takes two-and-a-half years to build a synchronous condenser. Like many industries, we have challenges due to delays in the supply chain.

It can take more than a year to get some of the larger components we need to be delivered to the job site. A project we are working on as lead project engineers has a 70-week lead time for a transformer to be delivered, which is about a 50 percent increase in lead time from what it used to be.

Compared to a traditional power plant covering hundreds of acres, synchronous condensers fit on one or less acre of land. The generator for these projects average 60-70 feet in length, and they are housed together with other components such as a transformer to connect to the transmission line and cooling fans.

The generator is the same type that would be used on a steam turbine, with the only difference being that there is nothing that drives it. It acts like a motor that is connected to the power system. It will draw power in to keep it turning, and then with the design of the generator, they can adjust the strength of the magnetic field, and the magnetic field creates the voltage and the VARs.

It will draw around three megawatts of power just to keep it turning, but they’ll be able to produce in the range of -180 to 360+ MVARs where a normal coal-fired power plant would produce +/- 100. This is a significant increase in the reactive power that can be produced from one generator replacing a power plant with eight generators. The -180 means that it can absorb VARs also. This wider range of operability is necessary because any unused energy will bounce back to the source.

Our role as lead project engineer on these types of projects is demanding and encompasses many facets of the project. This includes participation in technical and update meetings every week with the design team, suppliers, and all major stakeholders; specification and drawing reviews; assisting with action items; supporting the owner’s interests in reviewing, commenting, and questioning vendors or others involved in the project; assisting project managers; providing input on the schedule, forecast, and other elements regarding electrical components; vendor surveillance; review submittals; onsite construction support; and act as the owner’s engineer to ensure correct installation.

What does the future hold?

Synchronous condensers are a unique application for a specific problem. It’s unique that this technology was developed in the 1950s to stabilize power systems, and their rediscovery appears to be the missing link between the industrial need for reactive power and the loss of so many power plants.

As plans move forward in different areas of the country to build new synchronous condensers, we expect them to be even larger than our current project. For example, one is currently being designed to produce up to 500 MVARs.

One of the biggest challenges for this type of project is predicting the need three or four years in advance. The process begins with a feasibility study and submitting a future capital year budget, so utilities will have two years of planning invested before they can approve a budget.

There are a lot of factors that go into planning this type of project. They must predict what renewable generation will go into service, and they need to know their plans for retiring equipment, but don’t necessarily know what another utility’s plans are for retirement, even though it impacts them due to interconnections.

Examples of industries that require this additional power include refineries, steel mills, and auto manufacturers.

Everyone thinks renewable energy is solving a lot of problems, but most don’t realize that it is causing problems, too. Thankfully, transmission and utility companies have discovered synchronous condensers as an answer to the changing needs in their industry.

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