Solar cell

A solar cell made from a monocrystalline silicon wafer

A monocrystalline solar cell

A solar cell (also called photovoltaic cell or photoelectric cell) is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect.

Assemblies of cells used to make solar modules which are used to capture energy from sunlight, are known as solar panels. The energy generated from these solar modules, referred to as solar power, is an example of solar energy.

Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.

Cells are described as photovoltaic cells when the light source is not necessarily sunlight. These are used for detecting light or other electromagnetic radiation near the visible range, for example infrared detectors, or measurement of light intensity.

SERCH about dc motors in EXTRA links

DC Motors

DC motors are fairly simple to understand. They are also simple to make and only require a battery or dc supply to make them run.

Here are some great sites which describe how DC motors work.

http://www.howstuffworks.com/motor.htm
http://www.members.home.net/rdoctors/ (misc motor information)

There are several types of basic DC motors you can build. They make super science fair projects.

http://fly.hiwaay.net/~palmer/motor.html (a simple dc motor using one battery)
http://www.exploratorium.edu/snacks/stripped_down_motor.html
http://www.hb.quik.com/~norm/motor/
http://members.tripod.com/simplemotor/ (a very clever design of a dc motor with a permanent magnet armature)
http://www.qkits.com/serv/qkits/diy/pages/QK77.asp
http://store.jalts.com/elmogekit.html Check out the SDK200 kit for $24. Looks like a nicely packaged kit.

External links

Wikimedia Commons has media related to: Electric motors

• Electricity museum: early motors
• Electric Motors and Generators, explanations with animations from the University of New South Wales.
• The Numbers Game: A Primer on Single-Phase A.C. Electric Motor Horsepower Ratings, Kevin S. Brady.
• Theory of DC motor speed control
• International Energy Agency (IEA) 4E Annex concerned with Energy Efficiency in Electric Motor Systems
• Interactive Animation of a 3-Phase AC Electric Motor
• Kinematic Models for Design Digital Library (KMODDL) - Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library of classic texts on mechanical design and engineering.
• How Printed Motors work
• Interactive Java Animation: The Rotating Magnetic Field
• Asynchronous Motor: Explanation of operation

Principles of operation in dc motors

Principles of operation

In any electric motor, operation is based on simple electromagnetism. A current-carrying conductor generates a magnetic field; when this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite (North and South) polarities attract, while like polarities (North and North, South and South) repel. The internal configuration of a DC motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion.

Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet or winding with a "North" polarization, while green represents a magnet or winding with a "South" polarization).

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. In most common DC motors (and all that BEAMers will see), the external magnetic field is produced by high-strength permanent magnets¹. The stator is the stationary part of the motor -- this includes the motor casing, as well as two or more permanent magnet pole pieces. The rotor (together with the axle and attached commutator) rotate with respect to the stator. The rotor consists of windings (generally on a core), the windings being electrically connected to the commutator. The above diagram shows a common motor layout -- with the rotor inside the stator (field) magnets.

The geometry of the brushes, commutator contacts, and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next winding. Given our example two-pole motor, the rotation reverses the direction of current through the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue rotating. In real life, though, DC motors will always have more than two poles (three is a very common number). In particular, this avoids "dead spots" in the commutator. You can imagine how with our example two-pole motor, if the rotor is exactly at the middle of its rotation (perfectly aligned with the field magnets), it will get "stuck" there. Meanwhile, with a two-pole motor, there is a moment where the commutator shorts out the power supply (i.e., both brushes touch both commutator contacts simultaneously). This would be bad for the power supply, waste energy, and damage motor components as well. Yet another disadvantage of such a simple motor is that it would exhibit a high amount of torque "ripple" (the amount of torque it could produce is cyclic with the position of the rotor).

So since most small DC motors are of a three-pole design, let's tinker with the workings of one via an interactive animation (JavaScript required):

You'll notice a few things from this -- namely, one pole is fully energized at a time (but two others are "partially" energized). As each brush transitions from one commutator contact to the next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs within a few microsecond). We'll see more about the effects of this later, but in the meantime you can see that this is a direct result of the coil windings' series wiring:

There's probably no better way to see how an average DC motor is put together, than by just opening one up. Unfortunately this is tedious work, as well as requiring the destruction of a perfectly good motor. Luckily for you, I've gone ahead and done this in your stead. The guts of a disassembled Mabuchi FF-030-PN motor (the same model that Solarbotics sells) are available for you to see here (on 10 lines / cm graph paper). This is a basic 3-pole DC motor, with 2 brushes and three commutator contacts.

The use of an iron core armature (as in the Mabuchi, above) is quite common, and has a number of advantages². First off, the iron core provides a strong, rigid support for the windings -- a particularly important consideration for high-torque motors. The core also conducts heat away from the rotor windings, allowing the motor to be driven harder than might otherwise be the case. Iron core construction is also relatively inexpensive compared with other construction types.

But iron core construction also has several disadvantages. The iron armature has a relatively high inertia which limits motor acceleration. This construction also results in high winding inductances which limit brush and commutator life.

In small motors, an alternative design is often used which features a 'coreless' armature winding. This design depends upon the coil wire itself for structural integrity. As a result, the armature is hollow, and the permanent magnet can be mounted inside the rotor coil. Coreless DC motors have much lower armature inductance than iron-core motors of comparable size, extending brush and commutator life.

Diagram courtesy of MicroMo

The coreless design also allows manufacturers to build smaller motors; meanwhile, due to the lack of iron in their rotors, coreless motors are somewhat prone to overheating. As a result, this design is generally used just in small, low-power motors. BEAMers will most often see coreless DC motors in the form of pager motors.

Again, disassembling a coreless motor can be instructive -- in this case, my hapless victim was a cheap pager vibrator motor. The guts of this disassembled motor are available for you to see here (on 10 lines / cm graph paper). This is (or more accurately, was) a 3-pole coreless DC motor. I disembowel 'em so you don't have to...

To get the best from DC motors in BEAMbots, we'll need to take a closer look at DC motor behaviors -- both obvious and not.

Photodiode cross section

1-1 Photodiode cross section

Measure Light Intensity using Photodiode

The Photodiode used is the BPW34. This is a high speed and high sensitive silicon PIN photodiode in a miniature flat plastic package. A photodiode is designed to be responsive to optical input. Due to its waterclear epoxy the device is sensitive to visible and infrared radiation. The large active area combined with a flat case gives a high sensitivity at a wide viewing angle.

Photodiodes can be used in either zero bias or reverse bias. Diodes have extremely high resistance when reverse biased. This resistance is reduced when light of an appropriate frequency shines on the junction. Hence, a reverse biased diode can be used as a light detector by monitoring the current running through it. Coupled to a 10Kohm resistor, and given the specification of the BPW34 a simple relationship between lux (light intensity) and voltage is given by

lux = 1333 * V_o

The Light Application Adaptor for the EMANT300 has the photodiode BPW34 connected to AIN0 (input analog) of the DAQ module and the resistor connected to AINCOM.

The LabVIEW VI that reads the voltage across the resistor and converts the voltage to lux is called EMANT300 Example Photodiode.VI

Front Panel

Block Diagram

Phototransistors

Phototransistors

Like diodes, all transistors are light-sensitive. Phototransistors are designed specifically to take advantage of this fact. The most-common variant is an NPN bipolar transistor with an exposed base region. Here, light striking the base replaces what would ordinarily be voltage applied to the base -- so, a phototransistor amplifies variations in the light striking it. Note that phototransistors may or may not have a base lead (if they do, the base lead allows you to bias the phototransistor's light response.

For phototransistor selection and comparison information, see the phototransistor section of the BEAM Reference Library's BEAM Pieces collection.

Note that photodiodes also can provide a similar function, although with much lower gain (i.e., photodiodes allow much less current to flow than do phototransistors). You can use this diagram to help you see the difference (both circuits are equivalent):

Photodiode

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Photodetector from a CD-ROM Drive. 3 photodiodes are visible.

Symbol for photodiode.

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.^[1] The common, traditional solar cell used to generate electric solar power is a large area photodiode.

Photodiodes are similar to regular semiconductor diodes except that they may be either exposed (to detect vacuum UV or X-rays) or packaged with a window or optical fiber connection to allow light to reach the sensitive part of the device. Many diodes designed for use specifically as a photodiode will also use a PIN junction rather than the typical PN junction.

how to connect a LDR

A photoresistor is a sensor whose resistance varies with light intensity. Most decrease in resistance as the light intensity increases. In a typical microcontroller application, this resistance must be converted to a voltage so that an A2D converter can measure it. The easiest way to do this is with a voltage divider circuit. A voltage divider is just two resistors in series connected between a voltage supply and ground. If R1 is connected to the voltage supply and R2 is connected to ground then the voltage at the junction between the two resistors is: If R1 is the photoresistor, the voltage will increase with increasing light intensity. If R2 is the photoresistor, the voltage will decrease with increasing light intensity. Sample Photoresistor Circuit

Using LDR desing circuit

design.

Figure 1 shows our initial design. As we did our lab, we noticed some of the weaknesses of the design, which we will mention in detail, and tried to improve our device.

Figure 1. Initial design for the solar seeker.

Our initial design was quite simple, we had 5V on one end of the photocell group and ground on the other end. If the same amount of light fell on both photocells the middle voltage would be 2.5V. In the second stage, we had a comparator that compared the photocell group middle voltage to 2.5V. If the photocell voltage was higher than 2.5V, meaning more light falls on the left photocell, the comparator would output 1 and then in the following step the H-bridge would force the servo to turn to the photocell group to the left, aiming to equalize the amount of incident light falling on both photocells.

Essentially, we were on the right track but we had some technical problems in our design

1- As it is, the servo motors would always turn full force! this meant that even if the photocells received slightly different amounts of light, the comparator would output a 1 or 0 and turn the motor as fast as it can. The situation is analogous to a soccer player trying to dribble the ball in a straight line but who is only allowed to kick the ball with full force.

2- The comparator typically outputs about 3.5V, but we would like to be able to have higher voltages around 12.

In order to solve problem 1, we used pulse width modulation, and for the second problem we used two buffers.

PULSE WIDTH MODULATION
So how does the pulse width modulator help us? In the previous setup, we used 2.5V only, now if we compare to a high frequency triangle wave, the output of the motor will be high for some fraction of time and low rest of the time. Effectively, this allows us to drive the motor with low voltages as well as high voltages.

Figure 2. Pulse width modulation.

As seen in Figure 2, the triangle wave results in the output voltage being high for some portion of the period and low for the rest. Analog input A causes the output to be low most of the time, this approximately corresponds to a voltage output of around 1V. Analog input B results in a 50% duty cycle that corresponds to a mean voltage output of 2.5V.

Now our analogous soccer player is able to have little touches on the ball to keep it in line.

BUFFERS
We would ideally like to have a voltage output of 12 Volts for the H-bridge, however the TTL logic high output is about 3.5V. In order to achieve 12V we used buffers.

Figure 3 shows our final design. the open-collector invertor is the 7406 and the buffer is the 7407.

Figure 3. Modified design for the solar seeker.

Applications of LDR

Applications

Photoresistors come in many different types. Inexpensive cadmium sulfide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarms, and outdoor clocks.

They are also used in some dynamic compressors together with a small incandescent lamp or light emitting diode to control gain reduction.

Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light dependent resistor) are used for the mid infrared spectral region. Ge:Cu photoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscop

Photoresistor

(Redirected from Light Dependent Resistor)

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The symbol for a photoresistor^[1]

A light dependent resistor

The internal components of a photoelectric control for a typical American streetlight. The photoresistor is facing rightwards, and controls whether current flows through the heater which opens the main power contacts. At night, the heater cools, closing the power contacts, energizing the street light. The heater/bimetal mechanism provides a built-in light level transient filter.

A photoresistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor.

A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor.

Sensors in Nature

Sensors in Nature

Further information: Sense

All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to:

• Light, motion, temperature, magnetic fields, gravity, humidity, vibration, pressure, electrical fields, sound, and other physical aspects of the external environment
• Physical aspects of the internal environment, such as stretch, motion of the organism, and position of appendages (proprioception)
• Environmental molecules, including toxins, nutrients, and pheromones
• Estimation of biomolecules interaction and some kinetics parameters
• Internal metabolic milieu, such as glucose level, oxygen level, or osmolality
• Internal signal molecules, such as hormones, neurotransmitters, and cytokines
• Differences between proteins of the organism itself and of the environment or alien creatures.

Sulfur hexafluoride circuit breaker

From Wikipedia, the free encyclopedia

Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in a medium, such as SF₆, having excellent dielectric and arc quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity.High-voltage circuit-breakers have greatly changed since they were first introduced about 40 years ago, and several interrupting principles have been developed that have contributed successively to a large reduction of the operating energy. These breakers are available for indoor or outdoor applications, the latter being in the form of breaker poles housed in ceramic insulators mounted on a structure.

Gas blast applied on the arc must be able to cool it rapidly so that gas temperature between the contacts is reduced from 20,000 K to less than 2000 K in a few hundred microseconds, so that it is able to withstand the transient recovery voltage that is applied across the contacts after current interruption. Sulphur hexafluoride is generally used in present high-voltage circuit-breakers (of rated voltage higher than 52 kV).

Into the 1980s, the pressure necessary to blast the arc was generated mostly by gas heating using arc energy. It is now possible to use low energy spring-loaded mechanisms to drive high-voltage circuit-breakers up to 800 kV.

An SF₆ circuit breaker rated 115 kV 1200 A installed at a hydroelectric generating station

Contents [hide] 1 Brief history 2 Thermal blast chambers 3 Self-blast chambers 4 Double motion of contacts 5 Comparison of single motion and double motion techniques 6 Thermal blast chamber with arc-assisted opening 7 Generator circuit-breakers 8 Evolution of tripping energy 9 Future perspectives 10 High Power testing 11 Issues related to SF6 Circuit Breakers 12 Alternatives to SF6 Circuit Breakers 13 Notes

[edit]Brief history

The first patents on the use of SF₆ as an interrupting medium were filed in Germany in 1938 by Vitaly Grosse (AEG) and independently later in the USA in July 1951 by H.J. Lingal, T.E. Browne and A.P. Storm (Westinghouse). The first industrial application of SF₆ for current interruption dates back to 1953. High-voltage 15 kV to 161 kV load switches were developed with a breaking capacity of 600 A. The first high-voltage SF₆ circuit-breaker built in 1956 by Westinghouse, could interrupt 5 kA under 115 kV, but it had 6 interrupting chambers in series per pole. In 1957, the puffer-type technique was introduced for SF₆ circuit breakers where the relative movement of a piston and a cylinder linked to the moving part is used to generate the pressure rise necessary to blast the arc via a nozzle made of insulating material (figure 1). In this technique, the pressure rise is obtained mainly by gas compression. The first high-voltage SF₆ circuit-breaker with a high short-circuit current capability was produced by Westinghouse in 1959. This dead tank circuit-breaker could interrupt 41.8 kA under 138 kV (10,000 MV·A) and 37.6 kA under 230 kV (15,000 MV·A). This performance was already significant, but the three chambers per pole and the high pressure source needed for the blast (1.35 MPa) was a constraint that had to be avoided in subsequent developments. The excellent properties of SF₆ lead to the fast extension of this technique in the 1970s and to its use for the development of circuit breakers with high interrupting capability, up to 800 kV.

The achievement around 1983 of the first single-break 245 kV and the corresponding 420kV to 550 kV and 800 kV, with respectively 2, 3, and 4 chambers per pole, lead to the dominance of SF₆ circuit breakers in the complete range of high voltages.

Several characteristics of SF₆ circuit breakers can explain their success:

• Simplicity of the interrupting chamber which does not need an auxiliary breaking chamber;
• Autonomy provided by the puffer technique;
• The possibility to obtain the highest performance, up to 63 kA, with a reduced number of interrupting chambers;
• Short break time of 2 to 2.5 cycles;
• High electrical endurance, allowing at least 25 years of operation without reconditioning;
• Possible compact solutions when used for "gas insulated switchgear" (GIS) or hybrid switchgear;
• Integrated closing resistors or synchronized operations to reduce switching over-voltages;
• Reliability and availability;
• Low noise levels.

The reduction in the number of interrupting chambers per pole has led to a considerable simplification of circuit breakers as well as the number of parts and seals required. As a direct consequence, the reliability of circuit breakers improved, as verified later on by CIGRE surveys.

[edit]Thermal blast chambers

New types of SF₆ breaking chambers, which implement innovative interrupting principles, have been developed over the past 30 years, with the objective of reducing the operating energy of the circuit-breaker. One aim of this evolution was to further increase the reliability by reducing the dynamic forces in the pole. Developments since 1980 have seen the use of the self-blast technique of interruption for SF₆ interrupting chambers.

These developments have been facilitated by the progress made in digital simulations that were widely used to optimize the geometry of the interrupting chamber and the linkage between the poles and the mechanism.

This technique has proved to be very efficient and has been widely applied for high voltage circuit breakers up to 550 kV. It has allowed the development of new ranges of circuit breakers operated by low energy spring-operated mechanisms.

The reduction of operating energy was mainly achieved by the lowering energy used for gas compression and by making increased use of arc energy to produce the pressure necessary to quench the arc and obtain current interruption. Low current interruption, up to about 30% of rated short-circuit current, is obtained by a puffer blast.

[edit]Self-blast chambers

Further development in the thermal blast technique was made by the introduction of a valve between the expansion and compression volumes. When interrupting low currents the valve opens under the effect of the overpressure generated in the compression volume. The blow-out of the arc is made as in a puffer circuit breaker thanks to the compression of the gas obtained by the piston action. In the case of high currents interruption, the arc energy produces a high overpressure in the expansion volume, which leads to the closure of the valve and thus isolating the expansion volume from the compression volume. The overpressure necessary for breaking is obtained by the optimal use of the thermal effect and of the nozzle clogging effect produced whenever the cross-section of the arc significantly reduces the exhaust of gas in the nozzle. In order to avoid excessive energy consumption by gas compression, a valve is fitted on the piston in order to limit the overpressure in the compression to a value necessary for the interruption of low short circuit currents.

Self-blast circuit breaker chamber (1) closed, (2) interrupting low current, (3) interrupting high current, and (4) open.

This technique, known as “self-blast” has now been used extensively since 1980 for the development of many types of interrupting chambers. The increased understanding of arc interruption obtained by digital simulations and validation through breaking tests, contribute to a higher reliability of these self-blast circuit breakers. In addition the reduction in operating energy, allowed by the self blast technique, leads to longer service life.

[edit]Double motion of contacts

An important decrease in operating energy can also be obtained by reducing the kinetic energy consumed during the tripping operation. One way is to displace the two arcing contacts in opposite directions so that the arc speed is half that of a conventional layout with a single mobile contact.

The thermal and self blast principles have enabled the use of low energy spring mechanisms for the operation of high voltage circuit breakers. They progressively replaced the puffer technique in the 1980s; first in 72.5 kV breakers, and then from 145 kV to 800 kV.

[edit]Comparison of single motion and double motion techniques

The double motion technique halves the tripping speed of the moving part. In principle, the kinetic energy could be quartered if the total moving mass was not increased. However, as the total moving mass is increased, the practical reduction in kinetic energy is closer to 60%.The total tripping energy also includes the compression energy, which is almost the same for both techniques. Thus, the reduction of the total tripping energy is lower, about 30%, although the exact value depends on the application and the operating mechanism.Depending on the specific case, either the double motion or the single motion technique can be cheaper. Other considerations, such as rationalization of the circuit-breaker range, can also influence the cost.

[edit]Thermal blast chamber with arc-assisted opening

In this interruption principle arc energy is used, on the one hand to generate the blast by thermal expansion and, on the other hand, to accelerate the moving part of the circuit breaker when interrupting high currents. The overpressure produced by the arc energy downstream of the interruption zone is applied on an auxiliary piston linked with the moving part. The resulting force accelerates the moving part, thus increasing the energy available for tripping.

With this interrupting principle it is possible, during high-current interruptions, to increase by about 30% the tripping energy delivered by the operating mechanism and to maintain the opening speed independently of the current. It is obviously better suited to circuit-breakers with high breaking currents such as Generator circuit-breakers.

[edit]Generator circuit-breakers

Generator circuit-breakers (GCB's) are connected between a generator and the step-up voltage transformer. They are generally used at the outlet of high power generators (100 MVA to 1800 MVA) in order to protect them in a reliable, fast and economic manner. Such circuit breakers must be able to allow the passage of high permanent currents under continuous service (6.3 kA to 40 kA), and have a high breaking capacity (63 kA to 275 kA).

They belong to the medium voltage range, but the TRV withstand capability required by ANSI/IEEE Standard C37.013 is such that the interrupting principles developed for the high-voltage range must be used. A particular embodiment of the thermal blast technique has been developed and applied to generator circuit-breakers. The self-blast technique described above is also widely used in SF₆generator circuit breakers, in which the contact system is driven by a low-energy, spring-operated mechanism. An example of such a device is shown in the figure below; this circuit breaker is rated for 17.5 kV and 63 kA.

Generator circuit breaker rated for 17.5 kV and 63 kA

[edit]Evolution of tripping energy

The operating energy has been reduced by 5 to 7 times during this period of 30 years. This illustrates well the great progress made in this field of interrupting techniques for high-voltage circuit-breakers.

[edit]Future perspectives

In the near future, present interrupting technologies can be applied to circuit-breakers with the higher rated breaking currents (63 kA to 80 kA) required in some networks with increasing power generation.

Self blast or thermal blast circuit breakers are now accepted world wide and they have been in service for high voltage applications for about 25 years by ABB, and later by Areva, starting with the voltage level of 72.5 kV^[1]. Today this technique is also available for the voltage levels 420/550/800 kV.

[edit]High Power testing

The short-circuit interrupting capability of high-voltage circuit breakers is such that it cannot be demonstrated with a single source able to generate the necessary power. A special scheme is used with a generator that provides the short-circuit current until current interruption and afterwards a voltage source applies the recovery voltage across the terminals of the circuit breaker. Tests are usually performed single-phase but can also be performed three-phase^[2]

[edit]Issues related to SF₆ Circuit Breakers

The following issues are associated with SF₆ circuit breakers

Greenhouse gas

Main article: Sulfur_hexafluoride#Greenhouse_gas

SF₆ is the most potent greenhouse gas that the Intergovernmental Panel on Climate Change has evaluated. It has a global warming potential that is 23,900 times worse than CO₂.^[3] SF₆ has been classified as a restricted gas under the Kyoto Protocol.^[4]

Toxic lower order gases

When an arc is formed in SF₆ gas small quantities of lower order gases are formed. Some of these byproducts are toxic and can cause irritation to eyes and respiratory system.

Oxygen displacement

SF₆ is heavier than air so care must be taken when entering low confined spaces due to the risk of oxygen displacement.

[edit]Alternatives to SF₆ Circuit Breakers

Circuit Breakers are usually classed on their insulating medium. The follow types of circuit breakers may be an alternative to SF₆ types.

• Air blast
• Oil
• Vacuum

[edit]Notes

1. ^ New interrupting and drive techniques to increase high voltage circuit breaker performance and reliability, CIGRE Session 1998, Paper 13-04
2. ^ Three-phase short-circuit testing of high-voltage circuit breakers, Presented by D.Dufournet & G.Montillet at IEEE switchgear committee meeting, May 1999
3. ^ "Sulfur hexafluoride (SF₆): global environmental effects and toxic byproduct formation". Retrieved 2009-08-02.
4. ^ "Potent New Greenhouse Gas Discovered". 31 July 2000. Retrieved 2009-08-02.