By Drew Robb

Gas turbine sales have been sluggish for years. Annual worldwide sales amounted to around 60 GW a decade or so ago. More recently, the range has sunk to 30 GW to 40 GW. 2022 saw a rebound back to 50 GW, though 2023 totals were down 12.6% at around 44 GW, according to Anthony Brough, a gas turbine analyst at Dora Partners.

One area where sales have been stronger is in the aeroderivative segment. Orders of the GE LM6000 and LM2500+ have been the major contributors, according to Brough. Worldwide, the LM2500 and the LM2500+ fleet is more than 2,500 units strong. The various models of LM6000 have accumulated around 1200 units.

The LM2500+ has found favor in LNG and other oil & gas applications around the world, as has the LM6000. But the LM6000 is also doing well in power generation applications. According to Dora Partners data, about 60 LM6000s have been sold in the last three years with many of these being the most recent model the LM6000 PF+.

“The vast majority of PF orders since 2019 have been of the PF+ variety, demonstrating the benefits and cost improvement on a $/kw basis) of its larger MW output units,” said Brough.

Many of these recent orders were converted to function both as power generators and in grid support.

The GE LM6000 PF+ gas turbine.

LM6000 evolution

The LM6000 was first introduced in the early 1990s. At the name aeroderivative implies, the LM6000 was derived from GE’s CF6 jet engine. Since its introduction, the LM6000 has been modified and upgraded several times. The PF+ gas turbine edition is the most recent upgrade, done in 2015. It increases the output as high as 57.1 MW compared to up to 51.1 MW for the LM6000 PC. The net heat rate of the PF+ is 8357 Btu/kWh (LHV) and its simple cycle efficiency is 40.8% (56% in combined cycle) with a ramp rate of 30 MW per minute and a cold startup time of five minutes. It can turn down to 50% load. It incorporates a dual-fuel Dry Low Emissions (DLE) combustor.

Morgan Hendry, President of SSS Clutch, said that LM6000 PF+ gas turbines are finding favor in applications such as synchronous condensing and grid support.

“We have delivered SSS Clutches over the past year for about 45 LM6000 PF+ to operate as synchronous condensing and to provide greater support for grids with a heavy presence of renewables,” said Hendry. “By placing the clutch between the power turbine and the generator, the machine can be turned into a synchronous condenser.” 

The clutch is there to help the unit shift its function. When not required for power production, the clutch is used to safely disconnect the turbine while allowing the generator to continue ­spinning. This provides renewable-heavy grids with much needed system stability and grid support.

As more and more coal and natural gas plants are taken offline, the grid lacks the system inertia provided by gas and steam turbines. If you remove too many of them, you can cause disruption. Power quality will drop, and a lack of inertia can lead to instability and potential blackouts.

An SSS Clutch placed between an LM6000 turbine and generator turns the machine into a synchronous condenser. Courtesy of SSS Clutch.

Understanding grid inertia

Generators and motors provide inertia as they rotate at the same frequency as the electricity grid. By doing so, gas turbines and steam turbines in natural gas-fired and coal plants act as a buffer against power spikes and changes in frequency. Such shifts come about due to the activities of the day. During peak periods, people turn on air conditioning, heating, lighting and appliances. At off-peak periods, these are not running. The ups and downs of demand cause frequency to rise and fall, sometimes rapidly.

Unseen by the consumer, a continual balancing act occurs. System operators work to maintain frequency in the correct range (60 Hz for the U.S). In extreme cases of frequency changes, utilities may have to “shed load” by disconnecting neighborhoods from the grid to avoid damaging equipment and keep the rest of the network in operation. If they fail to do this, the entire grid is in danger of collapse. This happened spectacularly in the Northeast U.S. in 2003 when 60 million people were left without power due to cascading failures in one part of the grid after another. On a smaller scale, similar events happened during blackouts in New York City and London during 2019.

The maintenance of grid inertia is one of the reasons behind the resurgence in LM6000 sales – and why others are retaining some of these turbines instead of retiring them. By repurposing their generators as synchronous condensers, they can offer grid stability and other ancillary services. If backup or peaking power generation is required in future, the plant can be restarted/recommissioned for generation.

North America already has many turbines operating as synchronous condensers. Examples include: Los Angeles Department of Water and Power (LADWP) has four GE aeroderivatives operating primarily as synchronous condensers but poised to provide generation when necessary; another four clutched LM6000 gas turbine generators operate at Commonwealth Chesapeake Power in Virginia; and a clutched GE aeroderivative is running at Calpine’s Cumberland Energy Center in New Jersey. The LM6000 PF+ appears to be the preferred model.

SaskPower in Canada has a fleet of LM6000s such as this one at its Ermine facility. The company recently ordered two SSS Clutches for its LM6000PF+ machines. Courtesy of SSS Clutch.

GT conversions

Hendry explained that it is relatively simple and inexpensive to convert a GT for use as a synchronous condenser. It can either operate purely as a synchronous condenser or can be set up to deliver real power or reactive power whenever desired.

Conversion is achieved by installing a synchro self-shifting (SSS) clutch between the turbine and the generator. The turbine brings the generator up to speed. Once the generator synchronizes with the grid, the turbine disconnects from the generator and shuts down. The generator uses grid power to keep spinning, constantly providing leading or lagging VARs as needed. The clutch disengages the prime mover and the generator when reactive power is needed. When real power is needed, the clutch automatically engages for power generation.

Repurposing existing machines can sometimes be challenging, added Hendry. One consideration is space, he said. There may not be sufficient room in the turbine hall to allow a clutch to be added. Control system modifications will also be needed. Specific to the LM6000 PF+, the clutch must be connected to a generator with a load gear built into it as these units run at a higher speed than the LM6000 PC to obtain more power.

Hendry listed a long list of recent clutch orders for the LM6000 PF+ alone: 30 for Tennessee Valley Authority (TVA), 10 of which have been delivered. Another three clutches delivered to Dominion Energy, and two more to SaskPower in Canada.

“As TVA is installing a GW of wind turbines and solar PV in Tennessee, the LM6000 PF+s will provide peaking power as well as system stability and reactive power support,” said Hendry.


About the Author: Drew Robb has been working as a full-time freelance writer in engineering and technology for the last 25 years. For more information, contact drew@robbeditorial.com.

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