uciradiuzivaj | elektrotehnika

ELEKTROTEHNIKA

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Electric Power Plants

Power Plant known also as a Power Station, is an industrial facility used to generate electricity. To generate power, a power plant needs to have an energy source. One source of energy is from the burning of fossil fuels, such as coal, oil and natural gas. Then we also have nuclear power, and finally renewable energy sources such as wind, solar and hydroelectric. Originally, the only source of power was Direct Current, or DC systems, but it wasn’t until Alternating Current, or AC systems were introduced that the power could be carried the distances necessary to be suitable for distribution to the masses.
Thermal Power Plants generate electricity by converting heat into electricity, essentially by burning a fuel. One example of this is a nuclear power plant. Nuclear power plants use reactors heat to turn water into steam. The steam is then sent through a turbine, which generates movement of a generator, which in turn generates electricity. A coal power plant works in much the same way, but instead of a nuclear reactor heating water to make steam, the heat from the burning coal powers a steam turbine.
Hydroelectric Power Plants generate power by converting the force of water to turn large generators. Hydroelectric Power Plants fall into three different categories. First up is “Impoundment”. An Impoundment facility typically uses a store of river water from a dam in a reservoir. When water is released from the reservoir, it flows through a turbine which generates motion. This turning motion activates a generator to produce electricity. Next up we have “Diversion”. A Diversion is fairly similar to an Impoundment facility, but may not need the use of a dam, but works by channeling a portion of a river through a canal or a penstock. The last type of Hydroelectric Power Plant is “Pumped Storage”. Pumped Storage stores its energy by pumping water uphill to a reservoir at a higher elevation. When there is a demand for power, the water is released from the high elevated reservoir into a lower reservoir. This generates electricity when it flows through a turbine generating motion, and electricity.
The next type of power plant is a solar power plant. This type of plant uses the suns energy to convert into electricity. This is achieved by using Photovoltaic, or PV panels, made up from a number of semiconductor cells that release electrons when they are exposed to the energy of the sun. Solar energy is one of the cleanest ways of generating electricity. The solar panels get connected to the grid and can be used to supplement a thermal power plant resources. They can be used in domestic environments too, and with the aid of batteries, can reduce households energy consumption drastically, without burning any fossil fuels.
Last, but not least, we have Wind Power Plants. Wind Power Plants, or Wind Turbines, get their energy from the wind by connecting a generator to the blades. The rotational movement of the blades caused by the wind, powers a generator. Like solar power, they are a clean source of energy, but require much more hardware to work effectively, and with many more parts, are more likely to fail.
Like many things nowadays, Power Plants are controlled using a PLC, Programmable Logic Controller, or DCS, Distributed Control System. The ability for condition monitoring of all the plant items enables us to determine what is running efficiently, and what could fail. This enables us to proactively maintain plant equipment before it fails, rather than reactively fixing broken equipment. From within a control room, a full SCADA, or a Supervisory Control And Data Acquisition system can monitor and control temperatures, speeds of pumps and motors and open and close valves. This can be especially useful in the case of fossil fuel burning plants where the precise control of system devices can increase the plant availability. Availability is the amount of time that the plant is able to produce electricity over a certain period of time, divided by the amount of the time in the period, which is often a Key Performance Indicator, or KPI. This also ensures the most efficient use of the plant which maximizes power generation. By monitoring the demand, and trending at which times of the day the demand is highest, plants can adjust the speed of pumps automatically according to the time of the day, something that wouldn’t be possible without the use of an automation control system.

Thermal Power Plant

The energy conversions that take place inside a fossil fuel plant change the energy stored in coal, oil or natural gas into electricity. It does so by utilizing the chemical energy stored in the fuel, burning it and then converting it into mechanical energy. This mechanical energy is utilized to operate an electrical generator to generate electricity. Such thermal power plants are designed on a large scale for continuous operation for years. The term fossil fuel refers to the fact that the sources of the fuels are the fossilized remains of plants and animals. Most of the energy conversions take place in three main components. These components are the boiler, the steam turbine and the generator. In a typical fossil fuel plant boiler, the tubes that form the walls of the boiler are filled with water that is under pressure. Fuel is fed in to the boiler where it is ignited and burned. As the fuel burns it releases thermal energy which is absorbed by the water in the tubes. As the water absorbs the thermal energy its temperature increases and it begins to boil. The boiling water changes into steam which is heated even more and then routed out of the boiler and sent to the turbine. So in the boiler the energy and fuel is converted into thermal energy and then the thermal energy goes into the steam that flows out of the boiler. Inside the turbine there are two kinds of blades: the blades that are attached to the casing are called stationary blades; the blades that are attached to the turbine shaft are called moving blades. When the steam strikes the blades that are attached to the shaft it causes them to move which makes the shaft rotate. In the process some of the energy and the steam is converted into mechanical energy in the turbine. Since the turbine shaft is connected to the generator this mechanical energy is transferred to the generator. In the generator the mechanical energy is converted into electricity. The steam that passes through the turbine next enters the condenser. In the condenser additional energy is removed from the low-pressure and low-temperature steam to cool it and convert it back into water. The water is then pumped through a series of heaters and back to the boiler where it's used again to produce more steam. The entire steam and water loop from the boiler through the turbine into the condenser back to the boiler is called the steam cycle. Like all power plants, fossil fuel plants have advantages and disadvantages. One of their biggest disadvantages is that fossil fuels are expensive and companies that operate fossil fuel plants have to keep buying fuel. Another disadvantage of fossil fuel plants is that the exhaust gas produced by burning fuel often contains harmful substances that must be removed before the gases can be released to the environment. Removing these substances can be costly and it can affect the efficiency of the plant. One of the advantages is that unlike hydroelectric plants fossil fuel plants aren't required to be located only where a dam can be built, for example.

A nuclear power plant works to a large extent like a conventional thermal power plant. Water is converted into steam which drives a turbine connected to a generator. This generator converts the mechanical energy into electrical energy; the only difference is that the heat which converts water into steam is produced by nuclear fission and not by burning coal, natural gas or biomass. The fission of the uranium begins by bombarding it with neutrons. In each fission two or three neutrons are released; they in turn cause new fissions and thus creating a chain reaction. Neutrons released by fissioning uranium atoms hit other uranium nuclei, causing them to split and release more neutrons. In a nuclear reactor it's important that this chain reaction is controlled. To control this, reactors use control rods made of materials like boron or cadmium, which absorb neutrons. By inserting these rods into the reactor core, the rate of the chain reaction can be slowed or even stopped. It's a delicate balance between keeping the reaction going to produce energy and making sure it doesn't go too far.

Hydroelectric Power Plant

Hydropower or hydroelectricity refers to the conversion of energy from flowing water into electricity. It is considered a renewable energy source because the water cycle is constantly renewed by the sun. One of the first uses of hydroenergy was for mechanical milling such as grinding grains but today modern hydro plants produce electricity using turbines and generators. The mechanical energy created by moving water spins rotors on a turbine - this turbine is connected to an electromagnetic generator which produces electricity when the turbine spins. There are two main types of hydroelectricity production: dams and run of river. Hydro dams utilize the potential energy from dammed water to produce electricity. A dam is a large barrier constructed to raise the level of water and control its flow. The elevation created by the dam creates gravitational force for turning the turbine when water is released. Some dams also contain an additional reservoir at their base where water is stored to be pumped to the higher reservoir for release when electricity is in demand. This is referred to as pumped storage hydro. The second form of hydroelectricity production is run of river hydro. Run of river still uses turbines and generators but relies on natural water flow rates of rivers diverting just a portion of the water through turbines. Because run of river hydro is subject to natural water variability, it is more intermittent than dammed hydro.

There are various sizes of hydro plants that produce electricity: large hydro greater than 30 megawatts, small hydro 100 kilowatts to 30 megawatts and micro hydro less than 100 kilowatts. Of all renewable energy sources hydropower holds the largest share of worldwide electricity production. Hydropower has several benefits; it is a cost competitive form of electricity even though the initial building cost can be high, it is quite reliable compared to other renewable options and pairs well with other sources as it can be used as base load power in some cases, dammed reservoirs can also help with flood control and be a reliable water supply for communities. There are also some concerns with hydropower especially when it comes to large dams. Damming a river has a major impact on the local environment changing wildlife habitats, blocking fish passage and often forcing people in riverside communities to move out of their homes. In addition dam failures can be catastrophic claiming the lives of those living downstream. Hydro plants are also not completely free of greenhouse gas emissions. As with most forms of energy carbon dioxide emissions happen during construction particularly due to the large quantities of cement used and plant matter in the flooded areas makes methane, another greenhouse gas as it decays underwater.