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9 power generating units grouped by prime mover you should know about

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Power generating units

Many types of power generating plants are in use and possible for the future, including steam plants fueled by coal, oil, or gas, nuclear plants, hydro plants and plants which use renewable energy.

9 power generating units grouped by prime mover you should know about
9 power generating units grouped by prime mover you should know about (on photo: SIEMENS SGT5-8000H / SGT5-8000H gas turbine)

Most types of power generating units can be grouped by prime mover – the type of device that drives the electric generator.

For example, the types of prime movers in use in the United States today are steam turbine, combustion turbine and reciprocating engines. Different fuels may be used for the various types of primer movers. The source of heat can be from the burning of coal, oil, gas or the heat given off in a nuclear reactor.

Let’s the following power generating units:

  1. Steam Turbines
  2. Combustion (Gas) Turbines
  3. Hydro Turbines
  4. Pumped Storage
  5. Nuclear Units
  6. Reciprocating Engines
  7. Micro Turbines
  8. Wind turbines
  9. Solar units

1. Steam Turbines

In a steam turbine generating plant fossil fuels (coal, oil, gas) are burned in a furnace. (In a nuclear plant heat is produced as a result of a nuclear chain reaction.) The heat given off by this combustion is used to heat water in a boiler to such a temperature that steam is produced.

This steam (which may be as hot as 1,000 degrees F and at pressures as high as 3,600psi) is then passed through one or more turbines. Energy contained in the steam is extracted by allowing the steam to expand and cool as it passes through the turbine(s).

472-megawatt steam turbine and generator (STG) for the Allen Combined Cycle Power Plant
472-megawatt steam turbine and generator (STG) for the Allen Combined Cycle Power Plant (photo credit: businesswire.com)

This energy turns the blades of the turbine, which are connected to a shaft. This shaft is connected to the electric generator and rotates the coils of the magnetic field of the generator, thus producing electricity. After passing through the turbine, the steam passes through a condenser, where it is cooled and becomes water for reintroduction to the boiler.

The functioning of a steam plant requires many pumps, fans, and auxiliary devices, particularly important are the feed water pumps, which force water through the boilers, the forced and induced draft fans, which provide sufficient air for the combustion in the boiler, and the system that injects the fuel into the boiler.

After leaving the turbine additional heat is extracted from the steam in feed water heaters, heating water going to the boiler. The steam is then condensed and fed back into the boiler.

Differences in the fuel used to produce heat will result in design and equipment differences for each generating station.

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2. Combustion (Gas) Turbines

Combustion turbines are most often fueled by gas but can be fueled with some liquids. In a combustion turbine hot gasses (ignited fuel–air mixture) burn, are expanded through a turbine, driving a generator. An additional component of a combustion turbine is a compressor. This device increases the pressure of the air used in the combustion section by a factor of approximately 10.

When the air is compressed in this manner, its temperature is increased. The resulting combustion of this heated air and fuel mixture raises the temperature of the gas to as much as 2,000°F.

This gas is then passed through a turbine, where it is cooled and expanded. The dissipated energy turns the turbine, which, in turn, runs an electrical generator. Gas turbines are not as efficient as steam plants, but are considerably lower in capital costs. For this reason they are often used as “peaking” plants to supply peak electricity needs.

There are several variations on this basic design, each attempting to make maximum use of the energy input to the system. In some cases the turbine exhaust gases are used to preheat air prior to combustion.

In other cases, the exhaust is used to heat steam in a boiler to operate in conjunction with a small steam turbine generator. This is known as a combined cycle plant. Combined cycle plants have excellent efficiency since a considerable amount of the energy in the gas turbine exhaust is recovered.

Gas-fired combined cycle generation plants are currently the units of choice in the United States.

However, I found interesting negative comment on this video by user C.W. If anybody has similar or oposite experience, feel free to share with me.

This unit creates an insane amount of noise pollution for the people who are unlucky enough to live on Roosevelt Island. There’s absolutely no protection from the noise the unit emits which is outrageous. It begins @ 6pm and goes for the next 12 hours, how on earth is that legal?? Why does this plant not have to abide by noise pollution policies every single other industry (including the airlines) must?

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3. Hydro Turbines

Electric power is produced from water by directing a column of falling water past the “fins” of a hydraulic turbine. In a typical hydroelectric power plant, water is contained behind a dam. This dam causes the water level to rise. As a result, potential energy is stored in the water. To produce electricity, the water is made to flow through a turbine to a lower level.

The difference in elevations between the two water levels is called the “head”.

In hydroelectric generation, the amount of electric energy that a given column of water is capable of producing varies directly with the head.

In the most common configuration, the hydraulic turbines and electrical generators are located at the site of the dam.

However, it is not uncommon to have the turbines and generators located several miles downstream from the dam. Under this arrangement, water flows through a large pipe or “penstock” from the dam to the turbines.

Electric power is produced from water by directing a column of falling water past the “fins” of a hydraulic turbine.
Hydro-power generating units at the Fionnay (290 MW) and Nendaz (390 MW) plants (photo credit: alpiq.com)

There are several types of hydroelectric plants in use today. In the simplest form, a stream or river is diverted to pass through a hydraulic turbine. However, daily and seasonal variations in stream flow will cause the output of the hydro project to change. To deal with this situation, storage ponds are built. A portion of the stream flow is diverted into the storage facility during normal or high-flow conditions.

Then, at low stream flow times, the water from the storage pond is released, thus maintaining the electric output of the project.

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4. Pumped Storage

In still other configurations, water is stored in a lower reservoir and pumped to a higher elevation reservoir at night by using low-cost electrical energy produced by the utility’s thermal plants at off peak times.

During the peak load hours, the water is released from the upper reservoir and passed through a turbine or turbines, which drive electric generators.

Often these turbine generators are reversible and used to pump the water in the lower reservoir back to the upper reservoir the next night. This type of hydroelectric station is known as pumped storage. On a net basis pumped storage plants do not produce electric energy but, in fact, consume energy, since about a third of the energy stored is lost in the process.

They also perform a “relay” function. They receive low-cost energy produced at one time and place, hold it for a while, and then pass it on for use at another time in other places when alternate energy sources would be more expensive.

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5. Nuclear Units

Nuclear units utilize a nuclear reaction as a source of heat for a conventional cycle. There are two primary designs used for nuclear reactors; boiling water reactors and pressurized water reactors. At the time of this writing, there are slightly more than 100 operating nuclear power units in the United States.

No new nuclear units have been installed in the United States for many years because of concern over capital costs and safety. As nuclear units age, some owners are requesting extensions of their operation licenses.

Other nuclear units are being retired.

Beloyarsk Nuclear Power Plant Unit 4, Sverdlovsk Oblast, Russia
Beloyarsk Nuclear Power Plant Unit 4, Sverdlovsk Oblast, Russia (photo credit: mundo.sputniknews.com)

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6. Reciprocating Engines

This type of generation usually consists of a large diesel engine which uses 2 diesel fuel as a source of energy. Electricity is produced by connecting the output shaft of the engine to an electrical generator.

Diesel engine improvements have resulted in considerable reductions in weight and improvement in efficiency.

This type of generation usually consists of a large diesel engine which uses 2 diesel fuel as a source of energy.
Reciprocating Engine

7. Micro Turbines

These are small turbines that can be located at or near the customers. They can be installed on the customer’s side of the meter or on the distribution or sub-transmission system, depending on their size.

They are usually fueled from the natural gas supply available.

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8. Wind turbines

The interest in renewable energy sources has also spurred the development of improved methods for wind energy generating electricity. The wind is used to drive a turbine, which drives a generator.

Due to the variable nature of the energy source, the speed of the wind turbine is not constant and machines other than synchronous generators have been applied. These include induction generators, DC generators, and variable reluctance generators.

The further development of power electronic controls will doubtlessly result in new configurations for wind power generating systems.

The effective generating capacity from wind power is considerably less than the capacity of the generators because there are periods when wind is not available.

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9. Solar units

Producing power directly from solar energy is not currently a significant factor in electricity generation. However, this technology has attracted the attention of electric utilities and industry as an alternative for future energy production.

Photovoltaics are semiconductor devices that convert solar radiation (sunlight) directly into electricity.

While the electricity is essentially free in that there are no fuel costs, photovoltaics have not been widely used, even in attractive climates due to the high initial investment required for the devices, their inability to produce power during periods of darkness, and the lack of knowledge about how long they will last.

They are economic, however, for applications where expensive extensions of wires is needed to provide normal electric service, for example, railroad crossings.

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Both wind power and solar power may need to be complimented with energy storage of some type to increase their effectiveness in supplying electricity requirements of the system.

Reference // Understanding electric power systems by Jack Casazza and Frank Delea

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Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on