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100-705: Maraetai Power Station is a hydroelectric power station on the Waikato River , in the North Island of New Zealand . It is the fifth of the eight hydroelectric power stations on the Waikato River, and at 360 MW, is the largest hydroelectric station on the Waikato. The station has two powerhouses - Maraetai I powerhouse is directly in front of the Maraetai Dam, while Maraetai II powerhouse

200-745: A greenhouse gas . According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant. In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2% to 8% of any kind of conventional fossil-fuel thermal generation. A new class of underwater logging operation that targets drowned forests can mitigate

300-463: A low-head hydro power plant with hydrostatic head of few meters to few tens of meters can be classified either as an SHP or an LHP. The other distinction between SHP and LHP is the degree of the water flow regulation: a typical SHP primarily uses the natural water discharge with very little regulation in comparison to an LHP. Therefore, the term SHP is frequently used as a synonym for the run-of-the-river power plant . The largest power producers in

400-403: A DC component flowing in the windings. A saturable reactor exploits saturation of the core to control alternating current. Knowledge of leakage inductance is also useful when transformers are operated in parallel. It can be shown that if the percent impedance and associated winding leakage reactance-to-resistance ( X / R ) ratio of two transformers were the same, the transformers would share

500-421: A flood and fail. Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Lower river flows will reduce the amount of live storage in a reservoir therefore reducing the amount of water that can be used for hydroelectricity. The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power. The risk of flow shortage may increase as

600-401: A flux equal and opposite to that produced by the primary winding. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the primary winding and a load connected to the secondary winding, the transformer currents flow in the indicated directions and

700-487: A higher speed of 187 rpm. The generators at Maraetai II produce 36 MW each at 11,000 volts. This is stepped-up by 40 MVA transformers to 220 kV for transmission. Electricity from both stations is sent to the Maraetai switchyard, between the two powerhouses. Electricity from the downstream Waipapa Power Station links into Maraetai via a single-circuit 220 kV line (MRI-WPA-A), and electricity from Maraetai and Waipapa

800-494: A hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel -powered energy plants. However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted. Construction of a hydroelectric complex can have significant environmental impact, principally in loss of arable land and population displacement. They also disrupt

900-809: A large natural height difference between two waterways, such as a waterfall or mountain lake. A tunnel is constructed to take water from the high reservoir to the generating hall built in a cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway. A simple formula for approximating electric power production at a hydroelectric station is: P = − η   ( m ˙ g   Δ h ) = − η   ( ( ρ V ˙ )   g   Δ h ) {\displaystyle P=-\eta \ ({\dot {m}}g\ \Delta h)=-\eta \ ((\rho {\dot {V}})\ g\ \Delta h)} where Efficiency

1000-670: A large transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. Transformers may require protective relays to protect the transformer from overvoltage at higher than rated frequency. One example is in traction transformers used for electric multiple unit and high-speed train service operating across regions with different electrical standards. The converter equipment and traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV). At much higher frequencies

1100-451: A larger amount of methane than those in temperate areas. Like other non-fossil fuel sources, hydropower also has no emissions of sulfur dioxide, nitrogen oxides, or other particulates. Reservoirs created by hydroelectric schemes often provide facilities for water sports , and become tourist attractions themselves. In some countries, aquaculture in reservoirs is common. Multi-use dams installed for irrigation support agriculture with

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1200-493: A nameplate that indicate the phase relationships between their terminals. This may be in the form of a phasor diagram, or using an alpha-numeric code to show the type of internal connection (wye or delta) for each winding. The EMF of a transformer at a given flux increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve

1300-432: A number of approximations. Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances. This introduces error but allows combination of primary and referred secondary resistances and reactance by simple summation as two series impedances. Transformer equivalent circuit impedance and transformer ratio parameters can be derived from

1400-433: A permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings. Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires. Later designs constructed

1500-592: A positive risk adjusted return, unless appropriate risk management measures are put in place. While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for aluminium electrolytic plants, for example. The Grand Coulee Dam switched to support Alcoa aluminium in Bellingham, Washington , United States for American World War II airplanes before it

1600-548: A relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. Managing dams which are also used for other purposes, such as irrigation , is complicated. In 2021 the IEA called for "robust sustainability standards for all hydropower development with streamlined rules and regulations". Large reservoirs associated with traditional hydroelectric power stations result in submersion of extensive areas upstream of

1700-540: A result of climate change . One study from the Colorado River in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-off by up to 40%. Brazil in particular is vulnerable due to its heavy reliance on hydroelectricity, as increasing temperatures, lower water flow and alterations in

1800-448: A small TV/radio). Even smaller turbines of 200–300 W may power a few homes in a developing country with a drop of only 1 m (3 ft). A Pico-hydro setup is typically run-of-the-river , meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream. An underground power station is generally used at large facilities and makes use of

1900-455: A source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a grid, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on

2000-414: A start-up time of the order of a few minutes. Although battery power is quicker its capacity is tiny compared to hydro. It takes less than 10 minutes to bring most hydro units from cold start-up to full load; this is quicker than nuclear and almost all fossil fuel power. Power generation can also be decreased quickly when there is a surplus power generation. Hence the limited capacity of hydropower units

2100-581: A total of 1,500 terawatt-hours (TWh) of electrical energy in one full cycle" which was "about 170 times more energy than the global fleet of pumped storage hydropower plants". Battery storage capacity is not expected to overtake pumped storage during the 2020s. When used as peak power to meet demand, hydroelectricity has a higher value than baseload power and a much higher value compared to intermittent energy sources such as wind and solar. Hydroelectric stations have long economic lives, with some plants still in service after 50–100 years. Operating labor cost

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2200-468: A transformer design to limit the short-circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative resistance , such as electric arcs , mercury- and sodium- vapor lamps and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders . Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers in circuits that have

2300-751: A year's worth of rain fell within 24 hours (see 1975 Banqiao Dam failure ). The resulting flood resulted in the deaths of 26,000 people, and another 145,000 from epidemics. Millions were left homeless. The creation of a dam in a geologically inappropriate location may cause disasters such as 1963 disaster at Vajont Dam in Italy, where almost 2,000 people died. Transformer Transformers are used to change AC voltage levels, such transformers being termed step-up or step-down type to increase or decrease voltage level, respectively. Transformers can also be used to provide galvanic isolation between circuits as well as to couple stages of signal-processing circuits. Since

2400-452: Is hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit. This may be stretched to 25 MW and 30 MW in Canada and the United States. Small hydro stations may be connected to conventional electrical distribution networks as

2500-478: Is a concrete arch dam which impounds the Waikato River behind the Maraetai I powerhouse, and creates Lake Maraetai. The dam is 133 metres (436 ft) long, 87 metres (285 ft) high, and is 15.2 metres (50 ft) wide at the base and 11 metres (36 ft) at the crest. At one time, the dam was the largest hydroelectric dam in the Southern Hemisphere . The dam's spillway is located south of

2600-635: Is also usually low, as plants are automated and have few personnel on site during normal operation. Where a dam serves multiple purposes, a hydroelectric station may be added with relatively low construction cost, providing a useful revenue stream to offset the costs of dam operation. It has been calculated that the sale of electricity from the Three Gorges Dam will cover the construction costs after 5 to 8 years of full generation. However, some data shows that in most countries large hydropower dams will be too costly and take too long to build to deliver

2700-519: Is at the expense of flux density at saturation. For instance, ferrite saturation occurs at a substantially lower flux density than laminated iron. Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components, such as caused in switching or by lightning. Transformer energy losses are dominated by winding and core losses. Transformers' efficiency tends to improve with increasing transformer capacity. The efficiency of typical distribution transformers

2800-402: Is between about 98 and 99 percent. As transformer losses vary with load, it is often useful to tabulate no-load loss , full-load loss, half-load loss, and so on. Hysteresis and eddy current losses are constant at all load levels and dominate at no load, while winding loss increases as load increases. The no-load loss can be significant, so that even an idle transformer constitutes a drain on

2900-457: Is diverted down a canal south of the dam to the powerhouse. The canal to Maraetai II is 550 metres (1,800 ft) long, 12 metres (39 ft) wide, and 12 metres (39 ft) deep. Water is taken from the canal to the powerhouse via five steel penstocks, slightly different from Maraetai I's. The penstocks are 102 metres (335 ft) long and 4.6 metres (15 ft) in diameter. The water is used to turn five Vertical Francis turbines, revolving at

3000-425: Is given by the universal EMF equation: A dot convention is often used in transformer circuit diagrams, nameplates or terminal markings to define the relative polarity of transformer windings. Positively increasing instantaneous current entering the primary winding's 'dot' end induces positive polarity voltage exiting the secondary winding's 'dot' end. Three-phase transformers used in electric power systems will have

3100-470: Is highest in the winter when solar energy is at a minimum. Pico hydro is hydroelectric power generation of under 5 kW . It is useful in small, remote communities that require only a small amount of electricity. For example, the 1.1 kW Intermediate Technology Development Group Pico Hydro Project in Kenya supplies 57 homes with very small electric loads (e.g., a couple of lights and a phone charger, or

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3200-445: Is initially produced during construction of the project, and some methane is given off annually by reservoirs, hydro has one of the lowest lifecycle greenhouse gas emissions for electricity generation. The low greenhouse gas impact of hydroelectricity is found especially in temperate climates . Greater greenhouse gas emission impacts are found in the tropical regions because the reservoirs of power stations in tropical regions produce

3300-471: Is located 550 metres (1,800 ft) downstream of Maraetai I. Although both are completely separate, both powerhouses are operated as one power station. Maraetai is owned and operated by Mercury Energy . In early 1946, the Minister of Public Works Bob Semple , announced a full development of the Waikato River, with the first three stations planned at Ohakuri , Whakamaru , and Maraetai. Although Ohakuri

3400-462: Is not an energy source, and appears as a negative number in listings. Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that only the water coming from upstream is available for generation at that moment, and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river. A tidal power station makes use of

3500-452: Is not generally used to produce base power except for vacating the flood pool or meeting downstream needs. Instead, it can serve as backup for non-hydro generators. The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost for dispatch later as high value clean electricity. In 2021, the IEA estimated that the "reservoirs of all existing conventional hydropower plants combined can store

3600-410: Is often higher (that is, closer to 1) with larger and more modern turbines. Annual electric energy production depends on the available water supply. In some installations, the water flow rate can vary by a factor of 10:1 over the course of a year. Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have

3700-421: Is rarely attempted; the 'real' transformer model's equivalent circuit shown below does not include parasitic capacitance. However, the capacitance effect can be measured by comparing open-circuit inductance, i.e. the inductance of a primary winding when the secondary circuit is open, to a short-circuit inductance when the secondary winding is shorted. The ideal transformer model assumes that all flux generated by

3800-550: Is taken from Lake Maraetai at the dam, and is conveyed to the powerhouse by five steel penstocks , each 70 metres (230 ft) long and 4.8 metres (16 ft) in diameter. The water is used to turn five Vertical Francis turbine , each revolving at 167 rpm. Water is then deposited back into the Waikato River. Each of the five turbines turns a generator, each generating 36 MW of electricity at 11,000 volts. For one megawatt of electricity to be generated, 2,000 litres (440 imp gal; 530 US gal) of water must pass through

3900-412: Is then transmitted to Whakamaru via two single-circuit 220 kV lines (MRI-WKM-A and MRI-WKM-B). From Whakamaru, electricity generated at Maraetai is distributed via Transpower 's 220 kV grid to Hamilton , Taupō , Palmerston North , and Auckland . Hydroelectric Hydroelectricity , or hydroelectric power , is electricity generated from hydropower (water power). Hydropower supplies 15% of

4000-679: The Bonneville Dam in 1937 and being recognized by the Flood Control Act of 1936 as the premier federal flood control agency. Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as "white coal". Hoover Dam 's initial 1,345 MW power station was the world's largest hydroelectric power station in 1936; it was eclipsed by the 6,809 MW Grand Coulee Dam in 1942. The Itaipu Dam opened in 1984 in South America as

4100-704: The HVDC Inter-Island ("Cook Strait cable") between the North and South Islands, following a significant increase in electricity demand. With the inter-island link completed in 1965, work recommenced on Maraetai II, with the first two turbines and generators were finally commissioned in July 1970. The last turbine and generator, and the last on the Waikato River, being commissioned in February 1971 - almost 25 years after construction of Maraetai began. Maraetai's dam

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4200-806: The International Exhibition of Hydropower and Tourism , with over one million visitors 1925. By 1920, when 40% of the power produced in the United States was hydroelectric, the Federal Power Act was enacted into law. The Act created the Federal Power Commission to regulate hydroelectric power stations on federal land and water. As the power stations became larger, their associated dams developed additional purposes, including flood control , irrigation and navigation . Federal funding became necessary for large-scale development, and federally owned corporations, such as

4300-633: The Tennessee Valley Authority (1933) and the Bonneville Power Administration (1937) were created. Additionally, the Bureau of Reclamation which had begun a series of western US irrigation projects in the early 20th century, was now constructing large hydroelectric projects such as the 1928 Hoover Dam . The United States Army Corps of Engineers was also involved in hydroelectric development, completing

4400-583: The Vulcan Street Plant , began operating September 30, 1882, in Appleton, Wisconsin , with an output of about 12.5 kilowatts. By 1886 there were 45 hydroelectric power stations in the United States and Canada; and by 1889 there were 200 in the United States alone. At the beginning of the 20th century, many small hydroelectric power stations were being constructed by commercial companies in mountains near metropolitan areas. Grenoble , France held

4500-468: The magnetizing branch of the model. Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency. The finite permeability core requires a magnetizing current I M to maintain mutual flux in the core. Magnetizing current is in phase with the flux, the relationship between the two being non-linear due to saturation effects. However, all impedances of

4600-506: The potential energy of dammed water driving a water turbine and generator . The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head . A large pipe (the " penstock ") delivers water from the reservoir to the turbine. This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand,

4700-433: The power grid . Ideal transformer equations By Faraday's law of induction: where V {\displaystyle V} is the instantaneous voltage , N {\displaystyle N} is the number of turns in a winding, dΦ/dt is the derivative of the magnetic flux Φ through one turn of the winding over time ( t ), and subscripts P and S denotes primary and secondary. Combining

4800-463: The IEA released a main-case forecast of 141 GW generated by hydropower over 2022–2027, which is slightly lower than deployment achieved from 2017–2022. Because environmental permitting and construction times are long, they estimate hydropower potential will remain limited, with only an additional 40 GW deemed possible in the accelerated case. In 2021 the IEA said that major modernisation refurbishments are required. Most hydroelectric power comes from

4900-482: The Second World War was quite surprisingly accepted by Cabinet, being one-third lower and one year faster than the lowest British offer. By mid-1951, the penstocks had been installed and the first three machines had been installed. On 31 October 1952, Maraetai generated its first electricity, producing 30 megawatts (40,000 hp)on a reduced load and half head . Temporary flumes transported water through

5000-464: The ability to transport particles heavier than itself downstream. This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation. Siltation can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam. Eventually, some reservoirs can become full of sediment and useless or over-top during

5100-595: The balance between stream flow and power production. Micro hydro means hydroelectric power installations that typically produce up to 100 kW of power. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks. There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel. Micro hydro systems complement photovoltaic solar energy systems because in many areas water flow, and thus available hydro power,

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5200-504: The constant water seepage, it was not uncommon for the workers to work in knee-high or even waist-high water. By 1948, some 800 workers were working on the site. The tunnel was completed in March 1949, when the northern portal was opened and the first water flowed through the tunnel. Work then started by building cofferdams to block the natural channel of the river and allow dam construction to begin. The Taupō control gates were shut to lower

5300-507: The core magnetomotive force cancels to zero. According to Faraday's law , since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of turns. The transformer winding voltage ratio is equal to the winding turns ratio. An ideal transformer is a reasonable approximation for a typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to

5400-456: The core, the transformer is core form; when windings are surrounded by the core, the transformer is shell form. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils. Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at

5500-400: The corresponding current ratio. The load impedance referred to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer model neglects many basic linear aspects of real transformers, including unavoidable losses and inefficiencies. (a) Core losses, collectively called magnetizing current losses, consisting of (b) Unlike

5600-404: The daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water's kinetic energy or undammed sources such as undershot water wheels . Tidal power is viable in a relatively small number of locations around

5700-463: The dam foundations. Extensive and careful grouting of the rock took place, reaching 200 feet (61 m) below the river bed, and along the sides for a length of 1,000 feet (300 m). The grouting involved drilling thousands of holes in the rock face, and 11,000 tonnes (11,000 long tons; 12,000 short tons) of cement was used in the process. Construction of the dam began in September 1950, and soon

5800-444: The dam. Because of the dam's location in a narrow gorge, there was insufficient space to construct an orthodox spillway, so the diversion tunnel used in construction was reconfigured to become the dam's spillway. The spillway tunnel is 521 metres (1,709 ft) long, and 7.6 metres (25 ft) in diameter, and is blocked by three spillway gates, each 7.1 metres (23 ft) high and 7.16 metres (23.5 ft) wide. Water for Maraetai I

5900-505: The dams, sometimes destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife. The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir. Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of

6000-705: The effect of forest decay. Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In 2000, the World Commission on Dams estimated that dams had physically displaced 40–80 million people worldwide. Because large conventional dammed-hydro facilities hold back large volumes of water, a failure due to poor construction, natural disasters or sabotage can be catastrophic to downriver settlements and infrastructure. During Typhoon Nina in 1975 Banqiao Dam in Southern China failed when more than

6100-440: The electrical supply. Designing energy efficient transformers for lower loss requires a larger core, good-quality silicon steel , or even amorphous steel for the core and thicker wire, increasing initial cost. The choice of construction represents a trade-off between initial cost and operating cost. Transformer losses arise from: Closed-core transformers are constructed in 'core form' or 'shell form'. When windings surround

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6200-448: The equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits. With sinusoidal supply, core flux lags the induced EMF by 90°. With open-circuited secondary winding, magnetizing branch current I 0 equals transformer no-load current. The resulting model, though sometimes termed 'exact' equivalent circuit based on linearity assumptions, retains

6300-399: The excess generation capacity is used to pump water into the higher reservoir, thus providing demand side response . When the demand becomes greater, water is released back into the lower reservoir through a turbine. In 2021 pumped-storage schemes provided almost 85% of the world's 190 GW of grid energy storage and improve the daily capacity factor of the generation system. Pumped storage

6400-581: The fifth and final machine in April. The lake was then raised to its full height of 200 feet (61 m) head. The construction of the Maraetai II powerhouse, the last powerhouse to be built on the Waikato River began in 1959, with a 500-metre long canal taking water down the south side of the gorge to the powerhouse. In 1961, work on Maraetai II was suspended when the newly elected National government , led by Sir Keith Holyoake , shifted priority to building

6500-424: The following series loop impedances of the model: In normal course of circuit equivalence transformation, R S and X S are in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared, ( N P / N S )  = a . Core loss and reactance is represented by the following shunt leg impedances of the model: R C and X M are collectively termed

6600-461: The following tests: open-circuit test , short-circuit test , winding resistance test, and transformer ratio test. If the flux in the core is purely sinusoidal , the relationship for either winding between its rms voltage E rms of the winding, and the supply frequency f , number of turns N , core cross-sectional area A in m and peak magnetic flux density B peak in Wb/m or T (tesla)

6700-412: The ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: (c) similar to an inductor , parasitic capacitance and self-resonance phenomenon due to the electric field distribution. Three kinds of parasitic capacitance are usually considered and the closed-loop equations are provided Inclusion of capacitance into the transformer model is complicated, and

6800-465: The ideal transformer identity : where L {\displaystyle L} is winding self-inductance. By Ohm's law and ideal transformer identity: An ideal transformer is linear , lossless and perfectly coupled . Perfect coupling implies infinitely high core magnetic permeability and winding inductance and zero net magnetomotive force (i.e. i p n p  −  i s n s  = 0). A varying current in

6900-443: The invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission , distribution , and utilization of alternating current electric power. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect

7000-501: The largest amount for the region since 1990. Meanwhile, globally, hydropower generation increased by 70 TWh (up 2%) in 2022 and remains the largest renewable energy source, surpassing all other technologies combined. Hydropower has been used since ancient times to grind flour and perform other tasks. In the late 18th century hydraulic power provided the energy source needed for the start of the Industrial Revolution . In

7100-750: The largest, producing 14 GW , but was surpassed in 2008 by the Three Gorges Dam in China at 22.5 GW . Hydroelectricity would eventually supply some countries, including Norway , Democratic Republic of the Congo , Paraguay and Brazil , with over 85% of their electricity. In 2021 the International Energy Agency (IEA) said that more efforts are needed to help limit climate change . Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%. In 2022,

7200-616: The late 19th century, the electrical generator was developed and could now be coupled with hydraulics. The growing demand arising from the Industrial Revolution would drive development as well. In 1878, the world's first hydroelectric power scheme was developed at Cragside in Northumberland , England, by William Armstrong . It was used to power a single arc lamp in his art gallery. The old Schoelkopf Power Station No. 1 , US, near Niagara Falls , began to produce electricity in 1881. The first Edison hydroelectric power station,

7300-445: The limitations of early electric traction motors . Consequently, the transformers used to step-down the high overhead line voltages were much larger and heavier for the same power rating than those required for the higher frequencies. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of

7400-455: The load power in proportion to their respective ratings. However, the impedance tolerances of commercial transformers are significant. Also, the impedance and X/R ratio of different capacity transformers tends to vary. Referring to the diagram, a practical transformer's physical behavior may be represented by an equivalent circuit model, which can incorporate an ideal transformer. Winding joule losses and leakage reactance are represented by

7500-662: The lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent. Shell form design tends to be preferred for extra-high voltage and higher MVA applications because, though more labor-intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage. Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel . The steel has

7600-488: The mid-1700s, French engineer Bernard Forest de Bélidor published Architecture Hydraulique , which described vertical- and horizontal-axis hydraulic machines, and in 1771 Richard Arkwright 's combination of water power , the water frame , and continuous production played a significant part in the development of the factory system, with modern employment practices. In the 1840s, hydraulic power networks were developed to generate and transmit hydro power to end users. By

7700-651: The natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding, dam failure can be catastrophic. In 2021, global installed hydropower electrical capacity reached almost 1,400 GW, the highest among all renewable energy technologies. Hydroelectricity plays a leading role in countries like Brazil, Norway and China. but there are geographical limits and environmental issues. Tidal power can be used in coastal regions. China added 24 GW in 2022, accounting for nearly three-quarters of global hydropower capacity additions. Europe added 2 GW,

7800-415: The nature of the site, the target completion date of 1951 became less achievable. Work on the diversion tunnel - 25 feet (7.6 m) in diameter and 1,685 feet (514 m) in length - began in late 1946 on the southern side of the site. However, work was slowed by large amounts of water that poured into the tunnel until it was extensively grouted with cement and bitumen and lined with concrete. Because of

7900-633: The plant site. Generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. The turbines also will kill large portions of the fauna passing through, for instance 70% of the eel passing a turbine will perish immediately. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed. Drought and seasonal changes in rainfall can severely limit hydropower. Water may also be lost by evaporation. When water flows it has

8000-444: The power supply. It is not directly a power loss, but results in inferior voltage regulation , causing the secondary voltage not to be directly proportional to the primary voltage, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance. In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in

8100-455: The powerhouse from the two remaining penstocks. The reduced head was maintained while the diversion tunnel was stopped with a huge 30-metre (98 ft) long concrete plug. The head was raised to 175 feet (53 m) in April 1953, and the station was officially opened on 5 September 1953 - two years after the target completion date. The fourth machine was installed in January 1954, followed by

8200-401: The primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termed leakage flux , and results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of

8300-450: The rainfall regime, could reduce total energy production by 7% annually by the end of the century. Lower positive impacts are found in the tropical regions. In lowland rainforest areas, where inundation of a part of the forest is necessary, it has been noted that the reservoirs of power plants produce substantial amounts of methane . This is due to plant material in flooded areas decaying in an anaerobic environment and forming methane,

8400-439: The ratio of eq. 1 & eq. 2: where for a step-up transformer a < 1 and for a step-down transformer a > 1. By the law of conservation of energy , apparent , real and reactive power are each conserved in the input and output: where S {\displaystyle S} is apparent power and I {\displaystyle I} is current . Combining Eq. 3 & Eq. 4 with this endnote gives

8500-492: The rock was required. Construction of Maraetai I began in 1946, with the construction of an access road from Tokoroa, and establishing services and accommodation for the workers of the dam. The service and accommodation camp formed the town of Mangakino , on the south shore of what would become Lake Maraetai . Problems were encountered right from the beginning - the Second World War had just ended, which meant there

8600-436: The same impedance. However, properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and winding weight. Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50–60 Hz) for historical reasons concerned mainly with

8700-637: The transformer core size required drops dramatically: a physically small transformer can handle power levels that would require a massive iron core at mains frequency. The development of switching power semiconductor devices made switch-mode power supplies viable, to generate a high frequency, then change the voltage level with a small transformer. Transformers for higher frequency applications such as SMPS typically use core materials with much lower hysteresis and eddy-current losses than those for 50/60 Hz. Primary examples are iron-powder and ferrite cores. The lower frequency-dependant losses of these cores often

8800-418: The transformer's primary winding creates a varying magnetic flux in the transformer core, which is also encircled by the secondary winding. This varying flux at the secondary winding induces a varying electromotive force or voltage in the secondary winding. This electromagnetic induction phenomenon is the basis of transformer action and, in accordance with Lenz's law , the secondary current so produced creates

8900-401: The turbines every second. Electricity from each generator is then conveyed to a 40 MVA transformer , where the electricity is stepped-up to 220 kV for transmission. A sixth penstock is fitted to Maraetai I, which takes water to two auxiliary turbines and generators. These generators are used to generate electricity for the requirements in both Maraetai I and Maraetai II. Water for Maraetai II

9000-555: The usual United Kingdom because of tight delivery dates, and British firms' lack of experience in constructing large turbines, generators and 220 kV equipment. Eventually, contracts were let to Canada for the generators and the United States for the turbines, both being more experienced and the price being 40% less than the British equivalent. For the spillway gates and frames, a tender from West Germany only five years after

9100-429: The water level in the Waikato, and 11 bulldozers frantically pushed spoil into the river to stop the natural flow. The process was hampered by unexpected heavy rain which caused the river to rapidly rise, with it taking 27 hours to finally dam the river's natural course. The spillway tunnel was then constructed, which dropped at a 45-degree angle to intersect with the diversion tunnel. In late 1949, work finally started on

9200-502: The work force had reached its peak of 1200. A large mechanised batching plant had been bought on site to produce in excess of 153,000 cubic metres (200,000 cu yd) of concrete that was required for the dam, which was reinforced with 5,000 tonnes (4,900 long tons; 5,500 short tons) of steel. For the first time in New Zealand, a system of cooling mass concrete was used. This involved embedded pipes through which refrigerated water

9300-524: The world are hydroelectric power stations, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations . Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundred megawatts are generally considered large hydroelectric facilities. Currently, only seven facilities over 10 GW ( 10,000 MW ) are in operation worldwide, see table below. Small hydro

9400-533: The world's electricity , almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power . Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once

9500-539: The world. The classification of hydropower plants starts with two top-level categories: The classification of a plant as an SHP or LHP is primarily based on its nameplate capacity , the threshold varies by the country, but in any case a plant with the capacity of 50 MW or more is considered an LHP. As an example, for China, SHP power is below 25 MW, for India - below 15 MW, most of Europe - below 10 MW. The SHP and LHP categories are further subdivided into many subcategories that are not mutually exclusive. For example,

9600-416: Was a great deal of shortages of labour and materials. The Public Works department's work-force was less than two-thirds of its pre-war size, with thousands of vacancies not filled. Concrete and steel were also in short supply, as steel imports were less than half their pre-war levels, and local contractors could only produce two-thirds of the required amount of concrete. Combined with industrial unrest and

9700-586: Was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In Suriname , the Brokopondo Reservoir was constructed to provide electricity for the Alcoa aluminium industry. New Zealand 's Manapouri Power Station was constructed to supply electricity to the aluminium smelter at Tiwai Point . Since hydroelectric dams do not use fuel, power generation does not produce carbon dioxide . While carbon dioxide

9800-424: Was chosen first, the choice soon shifted to Whakamaru as it would be the best location for transmission needs. However, more investigation had been done for the Maraetai site, and starting Whakamaru first would make it more complex to divert the river for Maraetai later, so it was decided to build Maraetai first. Investigations into a hydroelectric station at Maraetai had been completed between 1940 and 1945. The site

9900-454: Was in a deep narrow gorge , west of Tokoroa and 20 miles (32 km) upstream of Arapuni . Because of the narrowness of the gorge, the powerhouse took up the entire length of the base of the dam, meaning no orthodox spillway could be constructed. This meant that the spillway had to be designed as part of the diversion tunnel. The site was composed of volcanic ignimbrite , which had cracked extensively on cooling meaning extensive grouting of

10000-473: Was passed. The powerhouse was constructed rapidly to have the machines operating as soon as possible. The foundations were started in early 1950, and the powerhouse was completed within a year. It consisted of a steel structural frame with a pre-cast concrete sectional roof. The transformer station was placed at the back and on top of the powerhouse itself due to the confines of the gorge. The Public Works Department wanted to source major equipment from outside

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