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Gas Turbine Coupled to Asynchronous Generator
It it possible to use an asynchronous generator coupled to a gas turbine in isolated system?
0 out of 1 members thought this post was helpful...

Hello All,

I'm working in a project for an oil company. The idea is couple a gas turbine to asynchronous generator for use in offshore application. The asynchronous generator have a narrow range of rpm where it work as generator. It is about 7 rpm for a two pole generator (3600 rpm in Brazilian system).

My question is: could the the gas turbine maintain control the rpm in this narrow range of rpm? The reactive power to the asynchronous generator will be provided from other two synchronous generators synchronized to it.

The structure of the system is: two synchronous generators 30MW each in parallel with the asynchronous generator of 25MW.

Thanks in advance
vladimircobas@gmail.com

1 out of 2 members thought this post was helpful...

vladimir36,

MANY off-shore applications use multiple gas turbine-driven synchronous generators from less than 3 MW to more than 40 MW--with no issues whatsoever. The governors of most gas turbines these days are very good at controlling speed (which is how frequency is controlled).

MANY ships use gas turbines for electric power generation as well as for main propulsion.

The biggest difficulties I have encountered with paralleling two, three, four or more synchronous generators is caused by choosing a supplier of a "power management system" to automatically control the units--and the supplier, while they may have excellent programmers and extensive experience with one or two of the major control systems, has very little--if ANY--experience with small power systems and controlling multiple synchronous generators and their prime movers. It can really be very ugly, and seldom gets properly resolved, much to the detriment of the owners, operators and technicians who have to struggle to find work-arounds--or even try to get a different company to come in, assess the situation and take on the task of righting a sinking ship.

Choose the supplier of a power management system based PRIMARILY on their proven experience of implementing successful power management systems. Do the really hard work of calling the references the prospective supplier(s) should gladly give you to ask about the installation, commissioning and after-sales service of the prospective supplier(s). It's not easy, but it's the best thing you can do to ensure a successful project--and a happy Customer. Choosing a supplier based on cost or reputation with applications other than power management systems will lead to headaches and heartaches for years.

Hope this helps!

1 out of 2 members thought this post was helpful...

vladimir36,

I've been doing some investigating because I don't really understand how an induction (asynchronous) generator could remain synchronized to a grid, or not disrupt a small independent power system (sometimes called a power island because it's isolated from a larger "infinite" grid).

Many modern wind turbines are a special kind of asynchronous generator with a wound rotor, called a doubly-fed induction generator. This allows them to remain synchronized to a grid when the wind turbine speed causes the frequency of the generator output to be higher (when the wind speed suddenly increases) or lower (when the wind speed is low). Reactive power can also be more easily controlled with a doubly-fed induction generator. (I'm NO expert on these machines as I've had EXACTLY zero training or exposure to them, so you'll have to search the World Wide Web for more information or visit your local library for reference books or texts on the subject.)

I still don't understand why an asynchronous generator is required for the application (and maybe you're not free to explain all the details). But I am a curious person by nature and I still like learning new things.

Hope this helps!

0 out of 1 members thought this post was helpful...

Thanks for your attention. My answers to your questions:

I've been doing some investigating because I don't really understand how an induction (asynchronous) generator could remain synchronized to a grid, or not disrupt a small independent power system (sometimes called a power island because it's isolated from a larger "infinite" grid).

I think the induction engine can generate synchronized to the grid because the rotating magnetic field of the estator have the same frequency of the small power island. The rotor is only to produce the torque inversion.

Many modern wind turbines are a special kind of asynchronous generator with a wound rotor, called a doubly-fed induction generator. This allows them to remain synchronized to a grid when the wind turbine speed causes the frequency of the generator output to be higher (when the wind speed suddenly increases) or lower (when the wind speed is low). Reactive power can also be more easily controlled with a doubly-fed induction generator. (I'm NO expert on these machines as I've had EXACTLY zero training or exposure to them, so
you'll have to search the World Wide Web for more information or visit your local library for reference books or texts on the subject.)

Yes the double feed induction generator is the best choice. the problem is the customer is reluctant to increase auxiliaries and weight.

My main question is how sensitive is the speed control of a Gas turbine? It can control the speed in a narrow range of rotations: let say between between 3600 and 3610?

I still don't understand why an asynchronous generator is required for the application (and maybe you're not free to explain all the details). But I am a curious person by nature and I still like learning new things.

If the assyncronous generator can operate in this isolated application (oil platform) it could reduce cost, weight, complexity. As on wind turbines.