The importance of speed in Turbine’s measurements

previous Measurement of speed of rotation

The power output of a wind turbine is proportional the cube of the speed. The speed is the most important parameter in evaluating the power from a turbine. It is often understated by manufacturers or misunderstood by buyers that the power rating of a wind turbine is only true at a given speed, know as the rated speed, which is neither too low nor too high, but somewhere where it is trusted that the wind turbine will be able to withstand the forces of rotation. These speeds are distinguished into four different regimes (Figure 5.13):

1. Start-up Speed – This is the speed at which the rotor and blade assembly begins to rotate.
2. Cut-in Speed –
   Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 10 mph for most turbines.
3. Rated Speed –
   The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph. At wind speeds between cut-in and rated, the power output from a wind turbine increases as the wind increases. The output of most machines levels off above the rated speed. Most manufacturers provide graphs, called "power curves," showing how their wind turbine output varies with wind speed.
4. Cut-out Speed –
   At very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed, or sometimes the furling speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Shut down may occur in one of several ways. In some machines an automatic brake is activated by a wind speed sensor. Some machines twist or "pitch" the blades to spill the wind. Still others use "spoilers," drag flaps mounted on the blades or the hub which are automatically activated by high rotor rpm's, or mechanically activated by a spring loaded device which turns the machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level.

Figure 5.13 Wind speeds for a wind turbine

Measurement of speed of rotation

previous Electrical Measurements

The following methods are used to measure the speed of rotation of an object: -

• Mechanical Tachometer
• Digital Tachometer
• Stroboscopes
• Magnetic Field Angular Position Sensors
• Wheel Encoder

The choice of technique used for measurement is governed by the application range considered, degree of accuracy required, type of installation and original cost. In this section each type will be discussed and an overview of the importance of time measurement will also be discussed.

Mechanical Tachometer

This type of tachometer is a linkage of shafts, gears and rotating weights. When the input shaft which is seen horizontal rotates the vertical shaft it also rotates the weights attached to it which are hinged and free to move inward and outwards. The movement of these flyweights rotates a pointer which is calibrated to give the speed in desired units such as RPM.

Two main drawbacks of this are that the mechanical weights have inertia and hence not very accurate and secondly it does not give an indication of the direction of rotation.

Figure 5.8 Mechanical Tachometer

Electrical Tachometers

This type of tachometer could be as simple as a DC or AC generator that can determine the speed of shaft rotation by the amount of voltage the generator produces or the frequency of the output signal. The magnitude of the generator voltage and the frequency of the generated voltage will increase proportionally with speed. Frequency can also be measured by a photocell tachometer. The number of pulses produced by the photocell will increase as the speed of the shaft rotation increases.

The rotating field and the toothed rotor tachometers produce a waveform and the photocell uses a rotating disk that has a number of windows in it. A light source is positioned so that it will shine light through each window in the disk to a photocell detector as the disk spins. The disk is connected to the tachometer shaft, so when it turns the windows line up with the photocell and the photocell produces a pulse when it is struck by light. In each of these types of tachometers a pulse stream is produced and it is proportional to the speed of the tachometer shaft.

Figure 5.9 Digital Tachometer

Stroboscope

Also known as the “strobe”, is an instrument used to make a cyclically moving object appear to be slow moving, or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating strings are common examples.

In electronic versions, the perforated disc is replaced by a lamp capable of emitting brief and rapid flashes of light. The frequency of the flash is adjusted so that it is an equal to, or a unit fraction below or above the object's cyclic speed, at which point the object is seen to be either stationary or moving backward or forward, depending on the flash frequency.

Figure 5.10 Stroboscope

In order to make a measurement, a mark is made on the object when it is stationary, and the object is spun up to speed. The oscillator is set to a low frequency to start with, and the LED is shone at the object where the mark is. At first, the mark will appear at random points around the object.

When it is stationary, the LED is flashing at the same frequency as the object is rotating. Since the frequency is known, the rotational speed is also known, and can be stated in RPM using the formula:

RPM = 60 × f_strobe
Magnetic Field Angular Position Sensors

These are similar shaft encoders, with one exception. They are capable of measuring the angle direction of a magnetic field from a magnet with <0.07° resolution. The advantages of measuring field direction versus field strength include: insensitivity to the temperature coefficient of the magnet, less sensitivity to shock and vibration, and the ability to withstand large variations in the gap between the sensor and magnet.

These sensors may be operated below 3 volts with a bandwidth response of 0-5 MHz. Output is a typical Wheatstone bridge permitting balanced output signals for noise immunity.

The main application of this sensor is to determine the angular position of a rotary axis. In this case, a permanent magnet is fixed on the engine axis just above the sensor. This magnet generates a directional magnetic field parallel to the surface of the sensor (Figure 5.11). This field works as a contactless interface between the orientation of the axis and the sensor.

Figure 5.11 The permanent magnet speed sensor.

Wheel encoder

Figure 5.12 shows an example of a typical encoder wheel. The resolution of the encoder wheel is determine by the number of cycles or complete phases.

Figure 5.12 Wheel Encoder

The encoder is a sensor attached to a rotating object (such as a wheel or motor) to measure rotation. A typical encoder uses optical sensor(s), a moving mechanical component, and a special reflector to provide a series of electrical pulses. These pulses can be used as part of a feedback control system to determine translation distance, rotational velocity of a rotating component.

For instance, to measure the time it takes motor to rotate exactly 360 degrees or more or less, an encoder would be ideal. The sensor would be fixed on the shaft (the encoder wheel) would rotate with the shaft. The output of an encoder would be a square wave, so if you hook up this signal to a digital counter or microcontroller you can then count the pulses. Knowing the distance/angle between each pulse, and the time from start to finish, you can easily determine position or angle or velocity of the motor.

next The importance of speed in Turbine’s measurements

Electrical Measurements

previous Wind Energy Measurements

Energy related measurements concerned with electricity production and consumption are usually derived from three elements namely: the electrical current, voltage and resistance of the load. These three variables are directly linked with the energy or power consumption of the load and hence it is common to see a single meter combining these to give a direct reading of the energy consumption.

Multimeters are very useful test instruments. By operating a multi-position switch on the meter they can be quickly and easily set to be a voltmeter, an ammeter or an ohmmeter. Two devices can be used to measure the electrical measurements: analog and digital multimeters as shown below in Figure. 5.3.

Figure 5.3 Digital and Analog Multimeters

As far as power is concerned, the most common unit of power consumption measurement on the electricity meter is the kilowatt hour, which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules. Some electricity companies use the SI mega joule instead. Modern electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) and finding the product of these to give instantaneous electrical power (watts) which is then integrated against time to give energy used (joules, kilowatt-hours etc). The meters fall into two basic categories, electromechanical and electronic, as shown in Figure. 5.4.

The mechanical electricity meter has every other dial rotating counter-clockwise. The most common type of electricity meter is the Thomson or electromechanical induction watt-hour meter, invented by Elihu Thomson in 1888. it work by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current.

A modern digital electronic wattmeter/energy meter samples the voltage and current thousands of times a second. The average of the instantaneous voltage multiplied by the current is the true power. The true power divided by the apparent volt-amperes (VA) is the power factor. A computer circuit uses the sampled values to calculate RMS voltage, RMS current, VA, power (watts), power factor, and kilowatthours. The simple models display that information on LCD. More sophisticated models retain the information over an extended period of time, and can transmit it to field equipment or a central location.

Figure 5.4 Measurement of Power

Wind speed is the most important factor directly proportional to the power output of a wind turbine.
Various types of anemometer are used to measure the velocity, usually of air.
The ‘cup type’ air speed measurement

(Figure 5.5) is used for free air and has hemispherical cups on arms attached to a rotating shaft. The shape of the cups gives a greater drag on one side than the other and results in a speed of rotation approximately proportional to the air speed. Velocity is found by measuring revolutions over a fixed time.

Figure 5.5 Cup Type Anemometer

The ‘vane anemometer’

(Figure 5.6) has an axial impeller attached to a handle with extensions and an electrical pick-up which measures the revolutions. A meter with several ranges indicates the velocity.

Figure 5.6 Vane Anemometer

The ‘hot-wire’ anemometer’

(Figure 5.7) is a probe terminating in an extremely small heated wire element when subjected to a fluid stream it cools to an extent, which depends on the velocity of the fluid passing. The resulting change in resistance of the element is measured by a bridge circuit and is related to velocity by calibration.

Figure 5.7 Hot-Wire Anemometer

next Measurement of speed of rotation

Halt Global Warming by Stopping Fossil Fuel Combustion

After years of warning the world about global warming and its dire consequences, Al Gore, the Nobel Prize winner, has finally taken the next, logical step. He is proposing a solution.

Mr. Gore has realized that conservation measures and "Cap and Trade" measures do not work. The world can be saved only, if we completely eliminate all carbon dioxide emissions during the next forty years.

Converting the electric power generating sector first, does make the most sense. All major technologies for generating electric power from renewable energy sources are in various stages of development. Installations using wind power, solar energy, geothermal heat, and marine power have been started up and are slowly gaining a measurable foothold.

At present, coal fired power plants generate the least expensive electricity. Therefore, market forces will never lead to the shutdown of the most egregious greenhouse gas emitters. Only legislative action can prevent the construction of any new, coal fired power plants.

We must also be aware that it will be very difficult to satisfy our growing electricity demand by building only windmill farms, solar plantations, and geothermal power plants. For many years to come, there will not be enough manufacturing capacity to build an adequate number of electric power plants using renewable energies. Initially, the capital costs of these plants will be high, risks for meeting rated output will be well above average, and elevated maintenance costs will be a common experience.

We also need to address a few unresolved technical issues. The most pressing one is the fact that both wind power and solar power can supply energy only on an interruptible basis. Electric power is a fleeting commodity and we have not yet developed technologies that are capable of storing large amounts of electric energy.

It seems unavoidable that nuclear power generation must assume a more substantial role during the next decades. Nuclear power has become safer and public resistance to nuclear power plants is slowly receding. Nuclear power plants can be installed faster once we begin to rely more on standardized reactor designs.

Nuclear reactors with smaller capacities need to be built as replacements for coal fired plant boilers. Huge amounts of capital and much time can be saved if existing coal plants can be retrofitted with steam produced in nuclear reactors to replace coal fired boilers. Steam turbines, generators, substations, administrative buildings, and cooling towers can continue their operation with only minor performance reductions.

This new type of reactor must be designed to be absolutely safe by installing both passive and redundant safety systems. Retrofit reactors should become available in a very few, standardized designs and in sizes that fit up with the predominant sizes of coal fired boilers in use.

While the US will be replacing, retrofitting, or shutting down its fossil fuel fired plants, it is an opportune time to prepare the US to regain its independence from foreign oil imports.

Very soon, such activity can save the US more than one trillion dollars annually. Past experience shows that petroleum prices and consumption of transportation fuels will maintain their unstoppable growths.

Ideally, the world will continue using its fleets of cars, trucks, trains, ships, and airplanes. Ideally, the world will keep its oil refineries operating and will preserve the huge distribution systems that deliver high quality liquid fuels to all corners of the world. Replacement of transportation fleets, oil refineries, and liquid fuel distribution systems will cost too much and may break the economies of even the richest countries.

We must realize that the world cannot live for more than a few weeks without transportation of foods, goods, and commodities. Famines, riots, and economic upheavals will become unavoidable consequences of the lack of plentiful and affordable transportation fuels.

To protect against such looming, economic disasters, the US must take the lead and learn how to produce petroleum substitutes from biomass. Recent events have taught us that we must never again abuse arable lands to make ethanol or diesel from food crops.

Instead, we must find plant species with very high energy contents and must grow these plants on arid and infertile lands. By using desalinated water and novel industrial farming techniques one can grow enough biomass to supply the entire world with transportation fuels for several centuries. Arid lands are abundant. Best of all, making petroleum substitutes from renewable biomass sources will not have to cost more than $50 per barrel.

Building plants for the domestic production of electric power and of transportation fuels from renewable energies will make the US strategically more secure, will make us economically stronger, will reduce global greenhouse gas emissions by one quarter, will create a huge number of jobs, and will pay for itself by producing large, domestic revenues for many decades to come.

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THE UNIQUE ROLE OF WIND TURBINE STEP-UP (WTSU) TRANSFORMERS

Introduction:
Harnessing wind energy to perform work is not a new concept.
Since the earliest of times, wind power has been captured with sails to allow traders,merchants and explorers to ply their trades and discover the world around them.
On land, windmills have been used for irrigation, grinding grains, and performing crude manufacturing for centuries. Even the generation of electricity from wind power is not a new idea. What is new, however, is the scale at which this renewable energy source is being used today.
Early wind generation served a local need, often supplying power for isolated
equipment. Today, wind energy represents nearly 5% of the US electrical generation and is targeted to reach 20% in the foreseeable future.
For this to happen, wind turbine outputs need to be gathered, stepped-up to
transmission levels and passed across the nation’s interconnected power grid to the end users. The role of the Wind Turbine Step-Up (WTSU) transformer in this process is critical and, as such, its design needs to be carefully and thoughtfully analyzed and reevaluated in our view.
Historically this WTSU transformer function has been handled by conventional, “off the shelf” distribution transformers, but the relatively large numbers of recent failures would strongly suggest that WTSU transformer designs need to be made substantially more robust. WTSU transformers are neither conventional “off the shelf” distribution transformers nor are they conventional “off the shelf” power generator step-up transformers. WTSU transformers fall somewhere in between and as such, we believe, require a unique design standard.
Although off-shore wind farms using dry-type transformers are beginning to grow in popularity, for this discussion we will look only at liquid-filled transformers that are normally associated with inland wind farm sites.
Transformer Loading:

Wind turbine output voltages typically range from 480 volts to 690 volts. This turbine output is then delivered to the WTSU transformers and transformed to a collector voltage of 13,800 to 46,000 volts. The turbines are highly dependant upon local climatic conditions; and this dependency can result in yearly average load factor as low as 35%. Both conventional distribution transformers and power generator step-up transformers are typically subjected to more constant loading at, or slightly above, their theoretical maximum rating. This high level of loading stresses insulation thermally and leads to reduced insulation life. On the other hand, the relatively light loading of WTSU transformer has a favorable effect on insulation life but introduces two unique and functionally significant problems with which other types of conventional transformers do not have to deal.

The first problem is that, when lightly loaded or idle, the core losses become a more significant economic factor while the coil or winding losses become less significant and de-emphasized. Typically used price evaluation formulae do not apply to this scenario. NEMA TP1 and DOE efficiencies are not modeled for the operational scenario where average loading is near 30-35% and, consequently, should be cautiously applied when calculating the total cost of ownership for WTSU transformers
The second problem is that the WTSU transformer goes into thermal cycling as a
function of these varying loads. This causes repeated thermal stress on the winding,clamping structure, seals and gaskets. Repeated thermal cycling causes nitrogen gas to be absorbed into the hot oil and then released as the oil cools, forming bubbles within the oil which can migrate into the insulation and windings to create hot spots and partial discharges which can damage insulation. The thermal cycling can also cause accelerated aging of internal and external electrical connections.
These cumulative effects put the WTSU transformer at a higher risk of insulation and dielectric failure than either the typical “off the shelf” distribution transformer or the power generator step-up transformer experiences.
Harmonics and Non-Sinusoidal loads:
Another unique aspect of WTSU transformers is the fact that they are switched in the line with solid state controls to limit the inrush currents. This differs widely from the typical step-up transformer which must be designed to withstand high magnetizinginrush currents which cause core saturation, and in the extreme Ferroresonance.
While potentially aiding in the initial energization, these same electronic controls
contribute damaging harmonic voltage frequencies that, when coupled with the nonsinusoidal wave forms from the wind turbines, cannot be ignored from a heating point of view. Conventional distribution transformers do not typically see non-linear loads that require preventative steps due to harmonic loading. When a rectifier/chopper system is used, the WTSU transformer must be designed for harmonics similar to rectifier transformers, taking the additional loading into consideration as well as providing electrostatic shields to prevent the transfer of harmonic frequencies between the primary and secondary windings, quite dissimilar to conventional distribution transformers.
Transformer sizing and voltage variation:
WTSU transformers are designed such that the voltage is matched to the generator (e.g. wind turbine) output voltage exactly. There is no “designed in” over-voltage capacity to overcome voltage fluctuations, as is typically done on distribution and power transformer designs which allow for up to 10% over-voltage. Further, it should be noted that the generator output current is monitored at millisecond intervals and the generator limited to allow up to 5% over-current for 10 seconds before it is taken off the system. Therefore, the WTSU transformer size ( kVA or MVA) is designed to match the generator output with no overload sizing. Since overload sizing is a common protective practice with “off the shelf” distribution or power step-up generator transformers, the WTSU transformer design must be uniquely robust to function without it.
Requirement to withstand Fault Currents:
Typically, conventional distribution transformers, power transformers, and other types of step-up transformers will “drop out” when subjected to an under-voltage or overcurrent situation caused by a fault. Once the fault has cleared, the distribution transformer is brought back on-line either individually or with it’s local feeder in conjunction with automatic reclosures. Wind turbine generators, on the other hand, in order to maintain network stability are only allowed to disconnect from the system due to network disturbances within certain, carefully controlled network guidelines developed for generating plants. Depending upon the specific network regulations, the length of time the generator is required to stay on line can vary. During this time the generator will continue to deliver an abnormally low voltage to the WTSU transformer.Therefore, during near-to generator faults, the generator may be required to carry as low as 15% rated voltage for a few cycles and then ramp back up to full volts a few seconds after fault clearing. This means that the WTSU transformer must be uniquely designed with enough “ruggedness” to withstand full short circuit current during the initial few cycles when the maximum mechanical forces are exerted upon the WTSU transformer windings.
Since wind turbines must stay connected during disturbances in the network, the WTSU transformers must be designed to withstand the full mechanical effects of short circuits.
Conclusions:
The role of WTSU transformers in today’s wind generation scheme is unique; it’s design must be equally unique and robust. The combination of wide variations in loading; harmonic loads from associated control electronics and generators; sizing without protection for over-voltages, under-voltages or over-loading; and the requirement to “ride through” transient events and faults sets the WTSU apart from it’s more conventional, “off the shelf” counterparts. It is neither a conventional distribution transformer nor is it a conventional generator step-up transformer.
“Off the shelf” . . . doesn’t belong . . . “down on the farm”!

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Advantages And Disadvantages Of Nuclear Energy

If you have even a passing interest in the topic of the advantages and disadvantages of nuclear energy, then you should take a look at the following information. This enlightening article presents some of the latest news on the different types of energy.

Energy prices are on the rise and it is becoming increasingly difficult for households to keep monthly energy expenses on a tight leash. Comparing energy prices from different service providers and switching to the less costly ones is an option that many consumers are trying out and succeeding to some extent.

Energy is a global commodity that is integral to nearly every aspect of society. The energy sector contains some of the oldest functional mechanical equipment and technology in the nation and is currently undergoing major changes in all aspects of the energy value chain. Energy is indeed "fuel for thought" and will continue to be so for many years to come. Energy Auditors use state of the art equipment to diagnose problems that may exist. Following their in-home 2-3 hour survey, they provide you with a detailed report highlighting any trouble spots and savings opportunities that they may have discovered.

See how much you can learn about the advantages and disadvantages of nuclear energy when you take a little time to read a well-researched article? Don't miss out on the rest of this great information.

Oil companies paid little attention to natural gas companies until recently. This could be the beginning of a big move where Chevron and others acquire companies with natural gas resources. Oil thug states control the supply, and it could be cut off. There might be reason to make imported oil very expensive, so that we would decrease our use of it.

Wind power makes this possible. Water desalinization can use in the coastal dry areas of Africa. Wind power is the fastest growing alternative energy system today. It is safe, simple, and clean, making it a good renewable energy source for homeowners.

Energy Saving Site provides alternative energy news, environmental articles, and energy saving tips. We focus on alternative energy because it is now being looked at as a means of fuelling our economy as we move away from oil dependence. Energy Saving Site serves both as a tutorial for understanding technology development and commercialization issues and as a central source for resources.

Energy conversion

previous Wind Turbines

It is important to understand that losses are encountered during the transformation of energy during the different conversions into the final form for a given application, for example consider a wind turbine, the following conversions take place:

Kinetic energy of the oncoming air strikes the rotor blades, turning them, and hence the axial kinetic energy is turned into mechanical energy of the rotating blades.

Some of this mechanical energy is lost in the control mechanism, consisting of the gear box and brake to regulate the speed and match it with that of the generator. Some energy losses are encountered due to friction.

The shaft turning with the remaining energy will rotate in turn the generator; hence converting it’s the output into electrical energy (mechanical to electrical).

Some losses are dissipated through the mechanical connections between the turbine and the electrical generator.

Electricity is used by customers for lighting / heating or to operate electric devices such as radio, television, etc. electrical devices are designed to operate on an optimum condition; efficiency of the operation will vary depending on its use, age and maintenance.

The energy flow for a typical wind turbine is shown in Figure 1.1; can be analysed in a simple way by considering the energy flow diagram, which may look like this:

100 units of energy are stored in the incoming air as kinetic energy.

40 units are converted into rotational /mechanical energy by the blades.

35 units are transferred by the shaft; some units are absorbed by the brake and gear.

33 units are converted from mechanical into electrical energy in the electrical generator.

30 units is the net output, as 3 units are lost in voltage conversion, storage and distribution.

The final figure depends on many factors, including the type of turbine, efficiency of the control system, efficiency of the generator, and the quality of the transformer and the distribution system.

Figure 1.1 Energy conversions in a typical Wind Turbine.

From \ To	Mechanical	Electrical	Thermal	Chemical	Nuclear
Mechanical	Gear Nutcracker push mower	Electric generator	friction	x
Electrical	Electric motor	Light bulb	Electric fire	Electrolysis	Particle accelerator
Thermal	Steam turbine	Thermocouple	Heat exchanger	x	Fusion reactor
Chemical	jet engine Rocket	Battery fuel cell	Car engine Boiler	Intermediate reaction	x
Nuclear	x	x	Nuclear reactor	x	x

Table 1.1 Energy conversion matrix

next Environmental Impact from fossil fuels

Wind Turbines

Energy and the Environment

Energy is needed for two functions:

1. To provide heating, cooking and processing of fluids
2. To provide electricity to drive machines, or power lights.

The following sections will discuss the various forms of energy, and how energy can be converted from one form to another which convenient for heating, cooling etc.

Forms of energy

We associate energy with devices whose inputs are fuel based such as electrical current, coal, oil or natural gas; resulting in outputs such as movement, heat or light.

Unit of energy is the Joule (J). The rate of producing energy is POWER which has the unit of Joule per second or the Watt (W).

There are FIVE forms of Energy:

1.  Mechanical Energy
2.  Electrical Energy
3. Chemical Energy
4. Nuclear Energy
5. Thermal Energy

These energy forms are discussed in the following sections.

Mechanical energy

This type of energy is associated with the ability to perform physical work.

There are two forms in which this energy is found; namely potential energy and kinetic energy.

Potential energy

As the name implies is contained in a body due to its height above its surroundings, examples such as the gravitational energy of the water behind a dam, and the energy stored in batteries.

Potential Energy = mass x acceleration due to gravity (9.81) x height above datum

E_p = m x g x h

The energy produced by one kilogram of water falling from a height of 100m above ground is a potential energy, which can be calculated as follows:

Potential Energy = mass x acceleration due to gravity x height above datum

E_p = 1 x 9.81 x 100 = 981 J/kg

Kinetic energy

Kinetic energy is related to the movement of the body in question. Examples of KE such as the flywheel effect and the energy of water flowing in a stream.

Kinetic Energy = ½ mass × velocity squared

E_k = ½ × m × v²

The water stream in a river flowing at a velocity of 2 m/s has a kinetic energy of:

Kinetic Energy = ½ mass × velocity squared = ½ × 1 × (2)² = 2 J/kg

Electrical energy

This type of energy as the name implies is associated with the electrons of materials. Electrical energy exists in two forms:

1. Electrostatic electricity
   This type of electrical energy is produced by the accumulation of charge on the plates of a capacitor. Charles Coulomb first described electric field strengths in the 1780's. He found that for point charges, the electrical force varies directly with the product of the charges. The greater the charges, the stronger the field. And the field varies inversely with the square of the distance between the charges. This means that the greater the distance, the weaker the force becomes. The formula for electrostatic force, F, is given as:
   F = k (q₁ × q₂) / d²
   Where q₁ and q₂ are the charges, d is the distance between the charges. And k is the proportionality constant which depend on the material separating the charges.
2. Electromagnetic energy
   This type is produced with a combination of magnetic and electric forces. It exists as a continuous spectrum of radiation. The most useful type of electromagnetic energy comes in the form of solar radiation transmitted by the sun that forms the basis of all terrestrial life.

Chemical energy

This type of is associated with the release of thermal energy due to a chemical reaction of certain substances with oxygen. Burning wood, coal or gas is the main source of energy we commonly use in heating and cooking.

Calculation of chemical energy

The energy liberated from the combustion of a given mass of fuel, with a known calorific value in a combustion chamber of known efficiency is given by:

Chemical Energy = Mass of fuel × calorific value × efficiency of combustion

Nuclear energy

This energy is stored in the nucleus of matter, and is released as a result of interactions within the atomic nucleus.

There are three nuclear reactions:

1. Radioactive decay:
   In which one unstable nucleus (radioisotope) decays into a more stable configuration resulting in the release of matter and energy.
2. Fission:
   A heavy nucleus absorbs a neutron splitting it into two or more nuclei accompanied by a release of energy. Uranium U235 has the ability to produce 70x10⁹ J/kg
   Einstein proposed the following equation to calculate the energy produced from nuclear fissioning (i.e. conversion of matter (m) into energy, E are related to the speed of light C) :
   E = m C²
   This reaction forms the bases for current nuclear power generation plants.
3. Fusion:
   Two light nuclei combine to produce a more stable configuration accompanied by the release of energy. Heavy water (Deuterium) fusion reaction may produce energy at the rate of 0.35x10¹² J/kg.
   This reaction is yet to be realized to produce electricity on commercial basis.

Thermal energy 

Thermal energy is associated with intermolecular vibration resulting in heat and a temperature rise above that of the surroundings. Thermal energy is calculated for two different regimes:

When the substance in a pure phase, say if it is in a liquid, gas or solid, then

Thermal Energy = mass x specific heat capacity x temperature difference

During a change of phase, such as evaporation or condensation, it can be calculated by:

Thermal Energy = mass x latent heat

However, if there is a change of phase, say during the condensation of water vapour into liquid, there is an additional amount of heat released while the temperature remains constant during the change of phase. For 1 kg of water to be heated at ambient pressure from 20 to 120 oC, the requirement is

Thermal energy = heating water (20-100)° C + evaporation at 100° C + super-heating vapour (100-120)° C

Thermal energy = 1 × 4.219 × (100-20) + 1x2256.7 + 1 × 2.01 × (120-100)

                      = 337.52 + 2256.7 + 40.2

                      = 2634.42 kJ

next Energy conversion