A transformer is a static electrical device that transfers electrical energy between two or more circuits. A varying current in one coil of the transformer produces a varying magnetic flux, which, in turn, induces a varying electromotive force across a second coil wound around the same core. Electrical energy can be transferred between the two coils, without a metallic connection between the two circuits. Faraday's law of induction discovered in 1831 described the induced voltage effect in any coil due to changing magnetic flux encircled by the coil. Transformers are used for increasing or decreasing the alternating voltages in electric power applications, for coupling the stages of signal processing circuits. Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission and utilization of alternating current electric power. A wide range of transformer designs is encountered in 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 the power grid.
An ideal transformer is a theoretical linear transformer, lossless and coupled. Perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force. A varying current in the transformer's primary winding attempts to create a varying magnetic flux in the transformer core, encircled by the secondary winding; this varying flux at the secondary winding induces a varying electromotive force in the secondary winding due to electromagnetic induction and the secondary current so produced creates a flux equal and opposite to that produced by the primary winding, in accordance with Lenz's law. 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 load impedance connected to the secondary winding, the transformer currents flow in the indicated directions and 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 windings. Thus, referring to the equations shown in the sidebox at right, according to Faraday's law, we have primary and secondary winding voltages defined by eq. 1 & eq. 2, respectively. The primary EMF is sometimes termed counter EMF; this is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field. The transformer winding voltage ratio is thus shown to be directly proportional to the winding turns ratio according to eq. 3. However, some sources use the inverse definition. According to the law of conservation of energy, any load impedance connected to the ideal transformer's secondary winding results in conservation of apparent and reactive power consistent with eq. 4. The ideal transformer identity shown in eq. 5 is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.
By Ohm's law and the ideal transformer identity: the secondary circuit load impedance can be expressed as eq. 6 the apparent load impedance referred to the primary circuit is derived in eq. 7 to be equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer model neglects the following basic linear aspects of real transformers: Core losses, collectively called magnetizing current losses, consisting of Hysteresis losses due to nonlinear magnetic effects in the transformer core, Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. Unlike the ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: Joule losses due to resistance in the primary and secondary windings Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance. Similar to an inductor, parasitic capacitance and self-resonance phenomenon due to the electric field distribution.
Three kinds of parasitic capacitance are considered and the closed-loop equations are provided Capacitance between adjacent turns in any one layer. 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 the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths; such flux is termed leakage flux, 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 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 under heavy load. Transformers are therefore designed to have low
Three-phase electric power
Three-phase electric power is a common method of alternating current electric power generation and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power, it is used to power large motors and other heavy loads. A three-wire three-phase circuit is more economical than an equivalent two-wire single-phase circuit at the same line to ground voltage because it uses less conductor material to transmit a given amount of electrical power. Polyphase power systems were independently invented by Galileo Ferraris, Mikhail Dolivo-Dobrovolsky, Jonas Wenström, John Hopkinson and Nikola Tesla in the late 1880s; the conductors between a voltage source and a load are called lines, the voltage between any two lines is called line voltage. The voltage measured across any one component is called phase voltage. In a symmetric three-phase power supply system, three conductors each carry an alternating current of the same frequency and voltage amplitude relative to a common reference but with a phase difference of one third of a cycle between each.
The common reference is connected to ground and to a current-carrying conductor called the neutral. Due to the phase difference, the voltage on any conductor reaches its peak at one third of a cycle after one of the other conductors and one third of a cycle before the remaining conductor; this phase delay gives constant power transfer to a balanced linear load. It makes it possible to produce a rotating magnetic field in an electric motor and generate other phase arrangements using transformers; the amplitude of the voltage difference between two phases is 3 times the amplitude of the voltage of the individual phases. The symmetric three-phase systems described here are referred to as three-phase systems because, although it is possible to design and implement asymmetric three-phase power systems, they are not used in practice because they lack the most important advantages of symmetric systems. In a three-phase system feeding a balanced and linear load, the sum of the instantaneous currents of the three conductors is zero.
In other words, the current in each conductor is equal in magnitude to the sum of the currents in the other two, but with the opposite sign. The return path for the current in any phase conductor is the other two phase conductors; as compared to a single-phase AC power supply that uses two conductors, a three-phase supply with no neutral and the same phase-to-ground voltage and current capacity per phase can transmit three times as much power using just 1.5 times as many wires. Thus, the ratio of capacity to conductor material is doubled; the ratio of capacity to conductor material increases to 3:1 with an ungrounded three-phase and center-grounded single-phase system. Constant power transfer and cancelling phase currents would in theory be possible with any number of phases, maintaining the capacity-to-conductor material ratio, twice that of single-phase power. However, two-phase power results in a less smooth torque in a generator or motor, more than three phases complicates infrastructure unnecessarily.
Three-phase systems may have a fourth wire in low-voltage distribution. This is the neutral wire; the neutral allows three separate single-phase supplies to be provided at a constant voltage and is used for supplying groups of domestic properties which are each single-phase loads. The connections are arranged so that, as far as possible in each group, equal power is drawn from each phase. Further up the distribution system, the currents are well balanced. Transformers may be wired in a way that they have a four-wire secondary but a three-wire primary while allowing unbalanced loads and the associated secondary-side neutral currents. Three-phase supplies have properties that make them desirable in electric power distribution systems: The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load; this makes it possible to reduce the size of the neutral conductor because it carries little or no current. With a balanced load, all the phase conductors so can be the same size.
Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations. Three-phase systems can produce a rotating magnetic field with a specified direction and constant magnitude, which simplifies the design of electric motors, as no starting circuit is required. Most household loads are single-phase. In North American residences, three-phase power might feed a multiple-unit apartment block, but the household loads are connected only as single phase. In lower-density areas, only a single phase might be used for distribution; some high-power domestic appliances such as electric stoves and clothes dryers are powered by a split phase system at 240 volts or from two phases of a three phase system at 208 volts. Wiring for the three phases is identified by color codes which vary by country. Connection of the phases in the right order is required to ensure the intended direction of rotation of three-phase motors. For example and fans may not work in reverse. Maintaining the identity of phases is required if there is any possibility two sources can be connected at the same time.
At the power station, an electrical generator converts mechanical pow
Flywheel energy storage
Flywheel energy storage works by accelerating a rotor to a high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy. Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are being developed. Advanced FES systems have rotors made of high strength carbon-fiber composites, suspended by magnetic bearings, spinning at speeds from 20,000 to over 50,000 rpm in a vacuum enclosure; such flywheels can come up to speed in a matter of minutes – reaching their energy capacity much more than some other forms of storage. A typical system consists of a flywheel supported by rolling-element bearing connected to a motor–generator; the flywheel and sometimes motor–generator may be enclosed in a vacuum chamber to reduce friction and reduce energy loss. First-generation flywheel energy-storage systems use a large steel flywheel rotating on mechanical bearings.
Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and can store much more energy for the same mass. To reduce friction, magnetic bearings are sometimes used instead of mechanical bearings; the expense of refrigeration led to the early dismissal of low-temperature superconductors for use in magnetic bearings. However, high-temperature superconductor bearings may be economical and could extend the time energy could be stored economically. Hybrid bearing systems are most to see use first. High-temperature superconductor bearings have had problems providing the lifting forces necessary for the larger designs, but can provide a stabilizing force. Therefore, in hybrid bearings, permanent magnets support the load and high-temperature superconductors are used to stabilize it; the reason superconductors can work well stabilizing the load is because they are perfect diamagnets. If the rotor tries to drift off center, a restoring force due to flux pinning restores it.
This is known as the magnetic stiffness of the bearing. Rotational axis vibration can occur due to low stiffness and damping, which are inherent problems of superconducting magnets, preventing the use of superconducting magnetic bearings for flywheel applications. Since flux pinning is an important factor for providing the stabilizing and lifting force, the HTSC can be made much more for FES than for other uses. HTSC powders can be formed into arbitrary shapes so long. An ongoing challenge that has to be overcome before superconductors can provide the full lifting force for an FES system is finding a way to suppress the decrease of levitation force and the gradual fall of rotor during operation caused by the flux creep of the superconducting material. Compared with other ways to store electricity, FES systems have long lifetimes, high specific energy, large maximum power output; the energy efficiency of flywheels known as round-trip efficiency, can be as high as 90%. Typical capacities range from 3 kWh to 133 kWh.
Rapid charging of a system occurs in less than 15 minutes. The high specific energies cited with flywheels can be a little misleading as commercial systems built have much lower specific energy, for example 11 W·h/kg, or 40 kJ/kg. Here m is the integral of the flywheel's mass, n m is the rotational speed; the maximal specific energy of a flywheel rotor is dependent on two factors: the first being the rotor's geometry, the second being the properties of the material being used. For single-material, isotropic rotors this relationship can be expressed as E I = K, where E is kinetic energy of the rotor, I is the rotor's moment of inertia, K is the rotor's geometric shape factor, σ is the tensile strength of the material, ρ is the material's density; the highest possible value for the shape factor of a flywheel rotor, is K = 1, which can only be achieved by the theoretical constant-stress disc geometry. A constant-thickness disc geometry has a shape factor of K = 0.606, while for a rod of constant thickness the value is K = 0.333.
A thin cylinder has a shape factor of K = 0.5. For energy storage, materials with high strength and low density are desirable. For this reason, composite materials are used in advanced flywheels; the strength-to-density ratio of a material can be expressed in Wh/kg. Several modern flywheel rotors are made from composite materials. Examples include the carbon-fiber composite flywheel from Beacon Power Corporation and the PowerThru flywheel from Phillips Service Industries. Alternatively, Calnetix utilizes aerospace-grade
A power inverter, or inverter, is an electronic device or circuitry that changes direct current to alternating current. The input voltage, output voltage and frequency, overall power handling depend on the design of the specific device or circuitry; the inverter does not produce any power. A power inverter can be electronic or may be a combination of mechanical effects and electronic circuitry. Static inverters do not use moving parts in the conversion process. Circuitry that performs the opposite function, converting AC to DC, is called a rectifier. A typical power inverter device or circuit requires a stable DC power source capable of supplying enough current for the intended power demands of the system; the input voltage depends on the purpose of the inverter. Examples include: 12 V DC, for smaller consumer and commercial inverters that run from a rechargeable 12 V lead acid battery or automotive electrical outlet. 24, 36 and 48 V DC, which are common standards for home energy systems. 200 to 400 V DC.
300 to 450 V DC, when power is from electric vehicle battery packs in vehicle-to-grid systems. Hundreds of thousands of volts, where the inverter is part of a high-voltage direct current power transmission system. An inverter can produce a square wave, modified sine wave, pulsed sine wave, pulse width modulated wave or sine wave depending on circuit design; the two dominant commercialized waveform types of inverters as of 2007 are modified sine wave and square wave. There are two basic designs for producing household plug-in voltage from a lower-voltage DC source, the first of which uses a switching boost converter to produce a higher-voltage DC and converts to AC; the second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage. This is one of the simplest waveforms an inverter design can produce and is best suited to low-sensitivity applications such as lighting and heating. Square wave output can produce "humming" when connected to audio equipment and is unsuitable for sensitive electronics.
A power inverter device which produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter. To more distinguish the inverters with outputs of much less distortion than the modified sine wave inverter designs, the manufacturers use the phrase pure sine wave inverter. All consumer grade inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave output at all, just a less choppy output than the square wave and modified sine wave inverters. However, this is not critical for most electronics. Where power inverter devices substitute for standard line power, a sine wave output is desirable because many electrical products are engineered to work best with a sine wave AC power source; the standard electric utility provides a sine wave with minor imperfections but sometimes with significant distortion. Sine wave inverters with more than three steps in the wave output are more complex and have higher cost than a modified sine wave, with only three steps, or square wave types of the same power handling.
Switch-mode power supply devices, such as personal computers or DVD players, function on quality modified sine wave power. AC motors directly operated on non-sinusoidal power may produce extra heat, may have different speed-torque characteristics, or may produce more audible noise than when running on sinusoidal power; the modified sine wave output of such an inverter is the sum of two square waves one of, phase shifted 90 degrees relative to the other. The result is three level waveform with equal intervals of zero volts; this sequence is repeated. The resultant wave roughly resembles the shape of a sine wave. Most inexpensive consumer power inverters produce a modified sine wave rather than a pure sine wave; the waveform in commercially available modified-sine-wave inverters resembles a square wave but with a pause during the polarity reversal. Switching states are developed for positive and zero voltages; the peak voltage to RMS voltage ratio does not maintain the same relationship as for a sine wave.
The DC bus voltage may be regulated, or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variations. The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called pulse width modulation; the generated gate pulses are given to each switch in accordance with the developed pattern to obtain the desired output. Harmonic spectrum in the output depends on the width of the modulation frequency; when operating induction motors, voltage harmonics are not of concern. Numerous items of electric equipment will operate quite well on modified sine wave power inverter devices loads that are resistive in nature such as traditional incandescent light bulbs. Items with a switch-mode power supply operate entirely without problems, but if the item has a mains transformer, this can overheat depending on how marginally it is rated. However, the load may operate less efficiently owing to the harmonics associated with a modified sine wave and produce a humming noise during operation.
This affects the efficiency of the system as a whole, since the manufa
An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson in 1904 for the generation of high-frequency alternating current for use as a radio transmitter. It was one of the first devices capable of generating the continuous radio waves needed for transmission of amplitude modulation by radio, it was used from about 1910 in a few "superpower" longwave radiotelegraphy stations to transmit transoceanic message traffic by Morse code to similar stations all over the world. Although obsolete by the early 1920s due to the development of vacuum-tube transmitters, the Alexanderson alternator continued to be used until World War II, it is on the list of IEEE Milestones as a key achievement in electrical engineering. After radio waves were discovered in 1887, the first generation of radio transmitters, the spark gap transmitters, produced strings of damped waves, pulses of radio waves which died out to zero quickly. By the 1890s it was realized. Efforts were made to invent transmitters that would produce continuous waves, a sinusoidal alternating current at a single frequency.
In an 1891 lecture, Frederick Thomas Trouton pointed out that, if an electrical alternator were run at a great enough cycle speed it would generate continuous waves at radio frequency. Starting with Elihu Thomson in 1889, a series of researchers built high frequency alternators, Nikola Tesla and Pyke, Parsons and Ewing, Siemens, B. G. Lamme, but none was able to reach the frequencies required for radio transmission, above 20 kHz. In 1904, Reginald Fessenden contracted with General Electric for an alternator that generated a frequency of 100,000 hertz for continuous wave radio; the alternator was designed by Ernst Alexanderson. The Alexanderson alternator was extensively used for long-wave radio communications by shore stations, but was too large and heavy to be installed on most ships. In 1906 the first 50-kilowatt alternators were delivered. One was to Reginald Fessenden at Brant Rock, another to John Hays Hammond, Jr. in Gloucester and another to the American Marconi Company in New Brunswick, New Jersey.
Alexanderson would receive a patent in 1911 for his device. The Alexanderson alternator followed Fessenden's rotary spark-gap transmitter as the second radio transmitter to be modulated to carry the human voice; until the invention of vacuum-tube oscillators in 1913 such as the Armstrong oscillator, the Alexanderson alternator was an important high-power radio transmitter, allowed amplitude modulation radio transmission of the human voice. The last remaining operable Alexanderson alternator is at the VLF transmitter Grimeton in Sweden and was in regular service until 1996, it continues to be operated for a few minutes on Alexanderson Day, either the last Sunday in June or first Sunday in July every year. Starting in 1942 four stations were operated by US Navy: the station at Haiku, Hawaii until 1958, Bolinas until 1946, Tuckerton. Two alternators were shipped to Hawaii in 1942, one each from Marion, MA and Bolinas, CA. Haiku received one; the other went to Guam but returned to Haiku after World War 2.
Haiku began operation of the first 200 kW alternator in 1943. The second alternator went into operation at Haiku in 1949. Both alternators were sold for salvage in 1969 to Kreger Company of California; the Marion station was transferred in 1949 to the US Air Force and used until 1957 for the transmission of weather forecasts to the arctic as well as for the Basen to Greenland and Iceland. One of the alternators was scrapped in 1961 and another one was handed over to the US office of standard, it now resides in a Smithsonian Institution warehouse; the two machines in Brazil were never used because of organizational problems there. They were returned to Radio Central after 1946; the Alexanderson alternator works to an AC electric generator, but generates higher-frequency current, in the low frequency radio frequency range. The rotor has no conductive windings or electrical connections; the space between the teeth is filled with nonmagnetic material, to give the rotor a smooth surface to decrease aerodynamic drag.
The rotor is turned at a high speed by an electric motor. The machine operates by variable reluctance; the periphery of the rotor is embraced by a circular iron stator with a C-shaped cross-section, divided into narrow poles, the same number as the rotor has, carrying two sets of coils. One set of coils is energized with direct current and produces a magnetic field in the air gap in the stator, which passes axially through the rotor; as the rotor turns, alternately either an iron section of the disk is in the gap between each pair of stator poles, allowing a high magnetic flux to cross the gap, or else a non-magnetic slot is in the stator gap, allowing less magnetic flux to pass. Thus the magnetic flux through the stator varies sinusoidally at a rapid rate; these changes in flux induce a radio-frequency voltage in a second set of coils on the stator. The RF collector coils are all interconnected by an output transformer, whose secondary winding is connected to the anten
The Diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel, injected into the combustion chamber, is caused by the elevated temperature of the air in the cylinder due to the mechanical compression. Diesel engines work by compressing only the air; this increases the air temperature inside the cylinder to such a high degree that atomised Diesel fuel injected into the combustion chamber ignites spontaneously. With the fuel being injected into the air just before combustion, the dispersion of the fuel is uneven; the process of mixing air and fuel happens entirely during combustion, the oxygen diffuses into the flame, which means that the Diesel engine operates with a diffusion flame. The torque a Diesel engine produces is controlled by manipulating the air ratio; the Diesel engine has the highest thermal efficiency of any practical internal or external combustion engine due to its high expansion ratio and inherent lean burn which enables heat dissipation by the excess air.
A small efficiency loss is avoided compared with two-stroke non-direct-injection gasoline engines since unburned fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed Diesel engines can reach effective efficiencies of up to 55%. Diesel engines may be designed as either four-stroke cycles, they were used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in ships. Use in locomotives, heavy equipment and electricity generation plants followed later. In the 1930s, they began to be used in a few automobiles. Since the 1970s, the use of Diesel engines in larger on-road and off-road vehicles in the US has increased. According to Konrad Reif, the EU average for Diesel cars accounts for 50% of the total newly registered; the world's largest Diesel engines put in service are 14-cylinder, two-stroke watercraft Diesel engines. In 1878, Rudolf Diesel, a student at the "Polytechnikum" in Munich, attended the lectures of Carl von Linde.
Linde explained that steam engines are capable of converting just 6-10 % of the heat energy into work, but that the Carnot cycle allows conversion of all the heat energy into work by means of isothermal change in condition. According to Diesel, this ignited the idea of creating a machine that could work on the Carnot cycle. After several years of working on his ideas, Diesel published them in 1893 in the essay Theory and Construction of a Rational Heat Motor. Diesel was criticised for his essay, but only few found the mistake that he made. Diesel's idea was to compress the air so that the temperature of the air would exceed that of combustion. However, such an engine could never perform any usable work. In his 1892 US patent #542846 Diesel describes the compression required for his cycle: "pure atmospheric air is compressed, according to curve 1 2, to such a degree that, before ignition or combustion takes place, the highest pressure of the diagram and the highest temperature are obtained-that is to say, the temperature at which the subsequent combustion has to take place, not the burning or igniting point.
To make this more clear, let it be assumed that the subsequent combustion shall take place at a temperature of 700°. In that case the initial pressure must be sixty-four atmospheres, or for 800° centigrade the pressure must be ninety atmospheres, so on. Into the air thus compressed is gradually introduced from the exterior finely divided fuel, which ignites on introduction, since the air is at a temperature far above the igniting-point of the fuel; the characteristic features of the cycle according to my present invention are therefore, increase of pressure and temperature up to the maximum, not by combustion, but prior to combustion by mechanical compression of air, there upon the subsequent performance of work without increase of pressure and temperature by gradual combustion during a prescribed part of the stroke determined by the cut-oil". By June 1893, Diesel had realised his original cycle would not work and he adopted the constant pressure cycle. Diesel describes the cycle in his 1895 patent application.
Notice that there is no longer a mention of compression temperatures exceeding the temperature of combustion. Now it is stated that the compression must be sufficient to trigger ignition. "1. In an internal-combustion engine, the combination of a cylinder and piston constructed and arranged to compress air to a degree producing a temperature above the igniting-point of the fuel, a supply for compressed air or gas. See US patent # 608845 filed 1895 / granted 1898In 1892, Diesel received patents in Germany, the United Kingdom and the United States for "Method of and Apparatus for Converting Heat into Work". In 1894 and 1895, he filed patents and addenda in various
An engine-generator or portable generator is the combination of an electrical generator and an engine mounted together to form a single piece of equipment. This combination is called an engine-generator set or a gen-set. In many contexts, the engine is taken for granted and the combined unit is called a generator. In addition to the engine and generator, engine-generators include a fuel supply, a constant engine speed regulator and a generator voltage regulator and exhaust systems, lubrication system. Units larger than about 1 kW rating have a battery and electric starter motor. Standby power generating units include an automatic starting system and a transfer switch to disconnect the load from the utility power source when there is a power failure and connect it to the generator. Engine-generators are available in a wide range of power ratings; these include small, hand-portable units that can supply several hundred watts of power, hand-cart mounted units, as pictured below, that can supply several thousand watts and stationary or trailer-mounted units that can supply over a million watts.
Regardless of the size, generators may run on gasoline, natural gas, bio-diesel, sewage gas or hydrogen. Most of the smaller units are built to use gasoline as a fuel, the larger ones have various fuel types, including diesel, natural gas and propane; some engines may operate on diesel and gas simultaneously. Many engine-generators use a reciprocating engine, with fuels mentioned above; this can be a steam engine, such as most coal-powered fossil-fuel power plants. Some engine-generators use a turbine as the engine, such as the industrial gas turbines used in peaking power plants and the microturbines used in some hybrid electric buses; the generator voltage and power ratings are selected to suit the load that will be connected. Engine-driven generators fueled on natural gas fuel form the heart of small-scale combined heat and power installations. There are only a few portable three-phase generator models available in the US. Most of the portable units available are single-phase generators and most of the three-phase generators manufactured are large industrial type generators.
In other countries where three-phase power is more common in households, portable generators are available from a few kW and upwards. Portable engine-generators may require an external power conditioner to safely operate some types of electronic equipment. Small portable generators may use an inverter. Inverter models can run at slower RPMs to generate the power, necessary, thus reducing the noise of the engine and making it more fuel-efficient. Inverter generators are best to power sensitive electronic devices such as computers and lights that use a ballast; the mid-size stationary engine-generator pictured here is a 100 kVA set which produces 415 V at around 110 A. It is powered by a 6.7-liter turbocharged Perkins Phaser 1000 Series engine, consumes 27 liters of fuel an hour, on a 400-liter tank. Diesel engines in the UK can rotate at 1,500 or 3,000 rpm; this produces power at 50 Hz, the frequency used in Europe. In areas where the frequency is 60 Hz, generators rotate at 1,800 rpm or another divisor of 3600.
Diesel engine-generator sets operated at their peak efficiency point can produce between 3 and 4 kilowatt hours of electrical energy for each liter of diesel fuel consumed, with lower efficiency at partial loads. Many generators produce enough kilowatts to power anything from a business to a full-sized hospital; these units are useful in providing backup power solutions for companies which have serious economic costs associated with a shutdown caused by an unplanned power outage. For example, a hospital is in constant need of electricity, because several life-preserving medical devices run on electricity, like ventilators. A common use is a railway diesel electric locomotive, some units having over 4,000 hp. Large generators are used onboard ships that utilize a diesel-electric powertrain. Voltages and frequencies may vary in different installations. Engine-generators are used to provide electrical power in areas where utility electricity is unavailable, or where electricity is only needed temporarily.
Small generators are sometimes used to provide electricity to power tools at construction sites. Trailer-mounted generators supply temporary installations of lighting, sound amplification systems, amusement rides etc. You can use a wattage chart to calculate the estimated power usage for different types of equipment to determine how many watts are necessary in a portable generator. Trailer-mounted generators or mobile generators, diesel generators are used for emergencies or backup where either a redundant system is required or no generator is on site. To make the hookup faster and safer, a tie-in panel is installed near the building switchgear that contains connectors such as camlocks; the tie-in panel may contain a phase rotation indicator and a circuit breaker. Camlock connectors are rated for 400 amps up to 480-volt systems and used with 4/0 type W cable connecting to the generator. Tie-in panel designs are common between 200- and 3000-amp applications. Standby electrical generators are permanently installed and used to provide electricity to critical loads during temporary interruptions of the utility power supply.
Hospitals, communications service installations, data processing ce