Circuit breaker with high voltage

Circuit breaker with high voltage is intended to establish, to support and to stop currents under its tension assigned (the maximum tension of the electrical communication which it protects), according to the definition given by the international electrotechnical Commission.
It operates at the same time:
under normal conditions of service, for example to connect or disconnect a line in an electrical communication
under specified abnormal conditions, in particular to eliminate a >court-circuit in the network caused by the lightning
From its characteristics, a circuit breaker is the apparatus of protection essential of a network with high voltage, because it is only able to stop a current of short-circuit and thus to prevent that the hardware connected on the network is damaged by this short-circuit.

Principle of operation

The cut of an electric current by a circuit breaker with high voltage is obtained while separating from the contacts in a gas or a layer insulating (for example oil or the vacuum). After separation of the contacts, the current continues to circulate in the circuit through an electric arc which was established between the contacts of the circuit breaker.
Arc enters the contacts of a circuit breaker to high voltage
To date, the circuit breakers with high voltage (72,5 Kv to 1100 Kv) use primarily gas or oil for insulation and the cut, the technique of vacuum breaker is limited to the applications into Medium Average with some recent developments for an assigned tension of 84 Kv
In the circuit breakers with gas, the current is shut off when a sufficient blowing is exerted on the electric arc to cool it and to stop it.
In a normal state, the gas contained in the circuit breaker is insulating, it makes it possible to support the tension of the network connected on its terminals. When the contacts of the circuit breaker separate, the interval between the contacts is subjected to a strong electric field, the current circulates then through an arc which is a plasma. The temperature of the arc becomes very high, it can reach 20000°C or more in the middle of the arc. Under the action of the blowing exerted on the arc during the operation of the circuit breaker, the temperature of the arc decreases, the electrons and the ions recombine and the fluid finds its insulating properties. The power cut then is successful.
For the circuit breakers with high voltage, the principle of cut retained is the cut of the current when it passes by zero (this occurs every ten milliseconds in the case of an alternative course with 50 Hz). Indeed, it is at this moment that the power which is provided to the arc by the network is minimal (this provided power is even null at the moment when the instantaneous value of the current is null), one can thus hope, with the help of a sufficient blowing, to make profitable this time interval during which the current is of low intensity to cool the arc sufficiently so that its temperature decreases and that space between the contacts becomes again insulator.

Techniques of cut

The first circuit breakers with high voltage, introduced at the end of the years 1890 and at the beginning of the twentieth century, used oil, water or the compressed air for the cut. The first patent of circuit breaker for the High voltage B, based on the separation of two contacts in oil (and the air), was deposited by Sebastian Ziani of Ferranti in July 1895. This principle will be improved thereafter and will give place to the circuit breakers with oil. The cut in the atmospheric air developed in High voltage has, the idea being then sufficiently to lengthen the arc in the air in order to cause its cooling, its extinction and then to ensure the behavior of the tension of the network
The technique of cut in oil was then supplanted by the vacuum breaker the compressed air, the SF6 and.

Circuit breaker with oil

The cut in oil was essential in high voltage after being developed into Medium Average (or High voltage A). Under the action of the electric arc, oil is broken up, several types of gas are produced (primarily hydrogen and acetylene) during this decomposition. The energy of the arc is used to break up and to evaporate oil, this makes it possible to cool the medium between the contacts and in consequence of stopping the current with its passage by zero.
The first circuit breakers with oil had arcing contacts which were plunged in oil contained in a metal tank with the potential of the ground, from where them name of Dead tank. They are called circuit breakers with large volume of oil. Some are always in service currently, for example in the United States.
Thereafter, in the years 1950, the circuit breakers with low volume of oil were designed to reduce the quantity of oil necessary and especially to limit the fire hazard inherent in the circuit breakers to large volume of oil. The arc develops in a cylinder insulating in order to limit its length and to control as much as possible the energy contained in the arc. This energy is used to generate blowing by vaporization of oil as previously explained. This technique which one calls by car-blowing will be taken again later for the circuit breakers with SF6. It was applied for assigned tensions reaching 765 Kv and of the very high fault currents, being able to reach 50 kA
These circuit breakers had for principal disadvantages of requiring many elements of cut in series (to hold the tension), and of requiring an important and delicate maintenance (replacement of waste oil). They were supplanted by the circuit breakers with SF6 which require little maintenance and have one long life of life.

Compressed-air circuit breaker

Compressed-air circuit breaker
The gas contained in the compressed-air circuit breakers is maintained under high pressure (20 to 35 bars) using a compressor. This high pressure makes it possible to ensure the dielectric behavior and to cause the blowing of the arc for the cut
The intense blowing exerted in these circuit breakers made it possible to obtain very high efficiencies (running crossed up to 100 kA under high voltage) and with one duration of very short elimination of the defect making it possible to ensure a good stability of the networks in the event of defect.
They had a long time the monopoly of very high efficiencies and during years 1960 and 1970 were used preferably in the networks with very high voltage, in particular in North America.
A defect of the compressed-air circuit breakers is their very important noise with the opening. Moreover, they require a routine maintenance, in particular of their compressors, this explains that they were gradually supplanted by another generation of circuit breakers, that of the circuit breakers with SF6 (or sulfur hexafluoride).
To note that the compressed-air technique is the only one which makes it possible still today to reach the highest breaking capacities (275 kA under 36 Kv) which are required for the circuit breakers of generators

Circuit breakers with vacuum bulbs

Vacuum bulb for circuit breaker with Medium Average
The first search and patents on the vacuum bulbs (switches) were made by California Institute off Technology about 1926. The first industrial applications were carried out to the end years 1950 when the technological difficulties of implementation were solved, in particular the guarantee of a high vacuum during at least twenty years, which requires a perfect sealing of the bulb
In a circuit breaker with vacuum, the arc is fed by the particles resulting from the contacts. The high dielectric behavior obtained in a high vacuum makes it possible to hold the transitory tension of re-establishment between contacts after interruption of the current. The passage of the current in contacts of suitable form generates a magnetic field which involves the rotation of the arc and prevents that this last remainder attached on the same surface of contact. It is thus possible to avoid the fusion of the contacts arcing and an excessive production of metal particles which would have limited the behavior of the tension after the interruption of the current.
Currently circuit breakers integrating of the bulbs into vacuum are in service up to 84 Kv, in Japan, the capacity breaking of a circuit breaker with vacuum can reach 63 kA. Search is in hand to develop bulbs with vacuum of higher tension

Circuit breaker with high voltage with the SF6 (sulfur Hexafluoride)

The use of the SF6 for the insulation was patented in the United States by Franklin Cooper of General Electric in 1938, and its use for the interruption of a current was also asserted in 1938 in a German patent by Vitaly Grosse of AEG (Allgemeine Elektrizitäts-Gesellschaft).
The first industrial application of the SF6 for the cut goes back to 1953, it was made by Westinghouse for charging switches to high voltage 15 Kv to 161 Kv with a breaking capacity of 600 has
The first realization of a circuit breaker SF6haute tension was made in 1956 by Westinghouse but the breaking capacity was then limited to 5 kA under 115 Kv (1000 Mva) and this apparatus was to have many elements of cut in series per pole to ensure the performances (six rooms of cut in series).
In same time, in 1957, the Workshops of Electrical engineerings of Delle produced a circuit breaker 23 Kv 250 Mva for cells of distribution, then a circuit breaker "Dead Tank" for engine 25 Kv 200 Mva
1959 should be waited until to see the production by Westinghouse of first circuit breaker SF6 to great breaking capacity: 41.8 kA under 138 Kv (10000 Mva) and 37,6 kA under 230kV (15000 Mva). This tripolar circuit breaker included/understood three rooms of cut in series per pole. It functioned with a relative pressure SF6 of 13,5 bar (above pression atmospheric) for blowing and of 3 bar relative to ensure the dielectric behavior. Performances were obtained thanks to the high pressures used, however these apparatuses presented the risk of liquefaction of the SF6 for temperatures lower than 5°C, it was thus necessary to envisage a maintenance in temperature of the tank high pressure.
The very good properties of the SF6 involved the extension of technique SF6 during the years 1960 and its use for the development of circuit breakers to strong breaking capacity under increasingly high tensions going up to 800 Kv and 1100 Kv since 2009 to China.
Net development high voltage and the need for making penetrate these networks inside the agglomerations and of the industrial parks involved the design of new types of stations with high-tension with small footprint of the "armor-plated" type or "under metal envelope". To ensure insulation, the atmospheric air was replaced by SF6, which has very good dielectric properties, which made it possible to strongly reduce the obstruction of equipment to high-tension.
The application of this technique in high voltage made it possible to realize since 1966 the first experimental prototype station armor-plated 220 Kv installed in Plessis-Gassot (close to Paris), and the first circuit breaker under metal envelope in 1967 in Levallois-Perret then in 1969 at the station of Vaise (Lyon, France)

Circuit breaker car-tire

Principle of the circuit breakers car-tires
The principle of blowing car-tire developed during the years 1970 and with the beginning of the year 1980 to answer the most demanding specifications and to develop increasingly powerful apparatuses
When the circuit breaker in position "is closed", the current forwards by contacts known as "permanent" which are located on the diameter external of the active part. During a release of the circuit breaker, the moving part moves to the bottom, involving the separation of the permanent contacts. The power is on then by another series of contacts, called "arcing contacts". When the moving part made a sufficient race, the arcing contacts separate, which causes the striking an arc between these contacts. The arcing contacts are carried out with materials containing tungsten so as to be able to support without damage the effects of the electric arc.
During the operation of opening, the circuit breaker produces itself the compression of gas necessary to the blowing of the arc. The relative displacement of the cylinder of blowing compared to the fixed piston creates an overpressure in the cylinder which is evacuated inside the tube and cools the arc, thus allowing its extinction.
The clarification of younger generations of very powerful circuit breakers SF6 involved in the years 1970 the supremacy of apparatuses SF6 in the range 7,2 Kv to 245 Kv.
As from 1983, the realization of the circuit breakers 245 Kv mono-cut (with an element of cut by pole), and of the corresponding apparatuses 420 Kv, 550 Kv and 800 Kv, led to the domination of technique SF6 in the whole of the range high voltage
Circuit breaker 115 Kv in Canada
On the technical plan, several characteristics of circuit breakers SF6 can explain their success:
The simplicity of the room of cut which does not require an auxiliary room for the cut (contrary to the compressed-air older apparatuses)
The autonomy of the apparatuses brought by the technique car-tire (without gas compressor)
The possibility of obtaining the highest performances, up to 63 kA, with a reduced number of rooms of cut: only one room is necessary in 245 Kv, one or two in 420 Kv and 550 Kv, generally four in 800 Kv
One duration of short elimination of defect, 2 to 2,5 cycles in very high voltage
A great electric endurance which makes it possible to guarantee one lifetime of at least 25 years
A reduction of the possible obstruction with the stations under metal envelope
The possibility of equipping the rooms with resistances of closing or of carrying out operations synchronized in order to very limit overpressures during the operations in high voltage
The reliability
A low noise level.
With the beginning of the year 1980, a new generation of circuit breakers SF6 to very high voltage was developed, with a simplified geometry which integrates a inseror of resistance of closing in the room of cut. In this case, resistance is located at the end of the room, inside an envelope metal but isolated from this one by the SF6 contained in the pole. This resistance is used to limit overpressures on the network during the interlocking or the reset of long lines with very high voltage.
The reduction of the number of rooms of cut involved a great simplification of the apparatuses by the reduction in the number of parts moving, the number of etc, seals It thus resulted an improvement from it from the reliability of the apparatuses which came to be added to the increase in the breaking capacity.

Circuit breaker with car-blowing

Principle of the circuit breakers with car-blowing
The period 1984-2000 was marked by the strong development of the means of calculation and modeling of circuit breakers SF6. Thanks to the use of these means, of new apparatuses with weak energy of operation were developed.
The circuit breakers with car-blowing are characterized by the important use of the energy of arc for the cut: blowing by car-blowing replaced mainly blowing car-tire for the cut of the strong currents. The cut of the low currents is always obtained by a blowing car-tire, the energy of the arc not being sufficient to contribute to blowing.
Figure 3 shows that during the phase of fort running, the arc started between contacts 7 and 8 transmits most of its energy to the thermal volume of expansion Vt. In the passing by zero of the current overpressure thus creates is drained through the insulating tube 9 and inside the mobile contact 7. This double blowing makes it possible to cool and stop effectively the arc. For the cut of the low currents a blowing auxiliary car-tire is carried out in volume Vp, the compressed gas coming to blow the arc via Vt volume.
An evolution of the rooms of cut with car-blowing consisted in introducing a valve (V) between the volume of expansion and the volume of compression.
Principle of the circuit breakers with car-blowing and double volume
In cut of weak currents the valve opens under the effect of the overpressure generated in the volume of compression. The blowing of the arc is carried out as in a circuit breaker car-tire thanks to the gas compression.
In the case of a cut of strong currents, the energy of arc produces a strong overpressure in the volume of expansion, which involves the closing of the valve (V) and isolates volume from expansion compared to the volume of compression. Overpressure necessary to the cut is obtained by an optimal use of the heating effect and stopper effect which occurs when the section of the arc significantly reduces the exhaust of gas in the tube.
To avoid an excessive consumption of energy by gas compression, a valve limits overpressure in the volume of compression to the value necessary for the cut of the weak currents of short-circuit.
A more recent evolution of the rooms of cut with car-blowing consisted in reducing the kinetic energy which must be provided by the body of operation during the opening of the circuit breaker. This is obtained by moving the two arcing contacts in opposed direction, so that the speed of each moving part is half of that of a unit record device. In this configuration, the mass moving is increased but the energy of operation is notably reduced since the kinetic energy varies like the square speed.
Circuit breaker with car-blowing with double movement of the contacts
The principle of cut with car-blowing made it possible to use commands with springs of weak energy for the operation of the circuit breakers high voltage. The apparatuses with car-blowing replaced the apparatuses car-tires during the years 1990-2003, first of all in 72,5 Kv, then of 145 Kv to 800 Kv.

Circuit breakers of generators

Circuit breaker of generator 17,5 Kv 63 kA with its body of operation in the foreground
These circuit breakers are connected between a generator of powerplant and the transformer which raises the tension before transport of electrical energy by the network.
The circuit breakers of generators are generally used on the outlet side of the generators of strong power (to 1800 Mva, in the case of nuclear plants) to protect them in a sure, fast and economic way.
These circuit breakers have a particular design because they must be able to forward very high currents in continuous service (6300A with 40000 has, and being also equipped with a very strong breaking capacity. Moreover, they must be able to shut off strong currents with a speed of re-establishment of the TTR which is much higher than that of the distribution systems used in the same range of tension.
The circuit breakers with cut in the SF6 are used when the breaking capacity does not exceed 160 kA or 210 kA, beyond, the compressed-air circuit breakers provide the highest breaking capacities which can be necessary, up to 275 kA.

Evolution of the circuit breakers with high voltage

The current evolution of the circuit breakers with high voltage is marked by:
the vulgarizing of strong breaking capacities (50 kA and 63 kA),
the reduction of energies of operation,
the reduction of the number of rooms of cut by pole,
the introduction of electronics inter alia for functions of self-diagnostic.
With regard to the circuit breakers with the SF6 and taking into account the significant impact the SF6 on the environment
The reduction of the escapes and the risks of escapes on the circuit breakers during the systems design.
The installation of procedures of checking, detection, localization and repair of the escapes for the period of exploitation of the product.
The recycling of gases at the end of the lifetime of the circuit breaker.
Thanks to the installation of these principles, the already weak impact in the beginning, is now control.

Performances of a circuit breaker with high voltage

The performances of the circuit breakers with high voltage are defined in international standards CEI and ANSI/IEEE. In this field, standards CEI are recognized in the majority of the countries in the world, whereas standards ANSI/IEEE are used primarily in North America.
Standard CEI 62271-100 is applicable to the circuit breakers with high voltage.
Like any electrical appliance with high voltage, a circuit breaker must have a level of assigned insulation and a closed-circuit current assigned in continuous service which ensures that the temperature of its parts will not exceed a standardized value.
Moreover one circuit breaker must have a breaking capacity assigned in the following cases:
power cut of lines with vacuum, cables with vacuum or of capacitor batteries
cut of defect at the boundaries
cut of defect on line
cut in discordance of phases
power cut of inductive loads for the circuit breakers which operate engines or reactances shunt.
The principal performance which characterizes a circuit breaker is its breaking capacity in short-circuit, that is to say the maximum current which it is able to stop under its assigned tension (maximum tension of the network where it is used). The values of the breaking capacity in short-circuit, expressed in effective value, lie typically between 25 kA and 63 kA (except the circuit breakers of generators). The current of short-circuit which can be stopped by a circuit breaker strongly depends on the tension which is restored at the boundaries of the circuit breaker after interruption of the current. This tension is restored first of all with high frequency oscillations, one calls then it the transitory tension of re-establishment (TTR), then it varies with the industrial frequency of the network.
A circuit breaker must also be able to establish a current of short-circuit whose peak value is normally equal to the product of its breaking capacity in short-circuit by 2,5 (networks with 50 Hz) or 2,6 (networks with 60 Hz).
Moreover, the circuit breakers of lines with high voltage must be able to engage or re-engage lines without causing overpressures on the Electrical communication. Two techniques are used to limit overpressures: the insertion of resistance to closing or an operation synchronized compared to the tension, with in this last case an objective of closing of the circuit when the terminal voltage of the circuit breaker is minimal.
These performances are checked by tests carried out full-scale, in accordance with the standards CEI 62271 or IEEE, in specialized laboratories. When they are higher than the power of the alternators of the laboratory, it is necessary to use a method, known as synthetic, with separate sources of current and tension.

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