EP0878983A1 - Control and driving system for a plasma torch - Google Patents

Abstract

A system for regulating and driving a plasma torch (1) comprises a store (34) for a graph of the arc voltage of the torch, known as the optimal voltage curve, as a function of the real electrical power provided to the torch, and a controller (124) for regulating the power of the torch. The system functions according to an operating condition called the ramp operating condition, so that the real power attains a value called the consigned value of power. This has an arc voltage which changes, with a small margin of error, with the optimum voltage. It also operates in another condition, called the permanent operating condition, in order to stabilise the real power around the consigned value, with an arc voltage equal, with a small margin of error, to the optimum voltage.

Description

Technical field and prior art

The invention relates to the field of torches with plasma; in particular, it concerns regulation and piloting a plasma torch.

• l'environnement, pour la destruction ou la vitrification de déchets dangereux,
• la chimie, pour la synthèse de certains produits,
• la sidérurgie et la métallurgie, pour le réchauffage de hauts fourneaux et de cubilots.

A plasma torch is a high power electrical device which delivers an ionized gas at high temperature (> 3500 ° C). It has industrial applications in fields which require very high temperatures such as:

• the environment, for the destruction or vitrification of hazardous waste,
• chemistry, for the synthesis of certain products,
• the steel and metallurgy industries, for the heating of blast furnaces and cupola furnaces.

The operation of a torch can be considered in itself. However, a torch is generally associated with an industrial process to which it provides thermal energy and with which it exchange of control data.

The operation of a plasma torch then requires the simultaneous implementation of several easements, controlled by an automatic system which provides the control / command function of the torch system.

The present invention therefore also relates to the operation of a plasma torch system (torch system), that is to say comprising a torch and a set of easements associated with it for fulfill its mission.

System automation design torch depends on its conditions of use in the process.

The torch can be inserted, for example partially in an oven heated to high temperature with a corrosive atmosphere. It is then cooled internally and externally.

The torch system must have a cycle of long operation with high reliability and sufficient continuous running time so as not to disrupt or prematurely stop the process industrial.

High-tech system, implementation of a plasma torch should however be kept simple and usable by operators with no specific knowledge.

Document EP-565,423 describes a system of piloting of a plasma torch.

In this prior art system, a measure of the arc voltage and the arc intensity is performed continuously. Control means allow to control the arc current and the gas flow plasmagen. Finally, a type of control valve pneumatic control is controlled by a positioner electropneumatic associated with a flow amplifier pneumatic. This makes it possible to make the valve opening and closing variations with variations in setpoints delivered by the Control measures.

Such a torch control system is complex and requires the implementation of means fairly frozen materials. In particular, the valve described in this document is mechanical fairly accurate. Furthermore, this control system is fixed for each torch and each application. It is possible to modify the setpoint values used, but a control system designed for a torch given or a given application is not compatible with another torch, different, or another application.

In addition, such a system does not optimize the torch operation. Document EP-565,423 does not gives no information on how to reach a setpoint power, nor on the problem of stabilization of the torch power when a power setpoint is reached.

This document also does not address the problem external disturbances such as variations humidity of the plasma gas or the state of wear of the electrodes. However, such disturbances can occur produce, especially after a period of use long enough of the torch.

In this case, the actual power supplied by the torch is affected, which is detrimental to its proper functioning as well as the maintenance of the process for which it is used.

Statement of the invention

There is therefore the problem of finding another plasma torch control system, more flexible to use than described above.

There is also the problem of making a regulation or control system from torch to plasma not requiring the use of a gate valve pneumatic control, with positioner and flow amplifier.

There is also the problem of finding a control system compatible with operation optimal torch, previously established.

Finally, there is also the problem of find a torch operation that is little disturbed by variations in gas composition plasma or by wear of the electrodes.

The invention provides a new system for regulation of a plasma torch to resolve the above problems.

• des moyens pour mémoriser une courbe de la tension d'arc de la torche, dite courbe de tension optimale, en fonction de la puissance électrique réelle fournie à la torche,
• des moyens pour commander une régulation de la puissance de la torche, et fonctionnant :
  • selon un premier régime, dit régime de rampe, afin que la puissance réelle atteigne une valeur dite valeur de consigne de la puissance, avec une tension d'arc qui évolue, à une marge d'erreur près, avec la tension optimale, ou qui suit, à une marge d'erreur près, la tension optimale,
  • selon un second régime, dit régime permanent, afin de stabiliser la puissance réelle autour de la valeur de consigne, avec une tension d'arc égale, à une marge d'erreur près, à la tension optimale.

The subject of the invention is a control system for a plasma torch, comprising:

• means for memorizing a curve of the arc voltage of the torch, known as the optimal voltage curve, as a function of the real electric power supplied to the torch,
• means for controlling regulation of the power of the torch, and operating:
  • according to a first regime, called ramp regime, so that the real power reaches a value known as the power reference value, with an arc voltage which evolves, with a margin of error, with the optimal voltage, or which follows, with a margin of error, the optimal tension,
  • according to a second regime, called permanent regime, in order to stabilize the real power around the set value, with an arc voltage equal, to within an error margin, at the optimal voltage.

By optimal tension is meant a tension previously chosen by the designer. For a given power, such an optimal voltage can be the voltage corresponding to a maximum efficiency of the torch and / or minimal wear of the electrodes.

Such a system does not require regulation mechanical air flow. In addition, such a system does not no problem with speed or acceleration of the response of an element to a command of the means of control.

Finally, such a system is compatible with all plasma torch system, because it only requires, for each torch, that knowledge of the function determining optimal functioning of the torch.

The means of regulation, during their ramp operation, allow reach a power setpoint.

The means of regulation, during their continuous operation, allow to stabilize the power of the ramp.

Such a system also offers the advantage depending on external disturbances ( variations in resistivity or gas pressure plasmagen, which is in direct contact with electrodes) which could possibly affect the poorly regulated torch operation. The system of regulation according to the invention is such that a defect of this type of plasma gas or supply circuit gas does not affect the torch system. Indeed, a variation in resistivity, or some other disturbance, produces a variation of the voltage which is brought back then at its optimal value.

Means may be provided to determine, depending on the difference between the power value actual electrical and the setpoint of the power, according to which of the two regimes the means of control must work.

Regulation control can be provided to act on the arc current values and / or the air flow to change the power values actual and arc voltage.

Such a system may further include means for modifying the power setpoint when the means of regulation operate in regime permanent; We then have a system that can function optimally, whatever setpoint changes imposed by the operator, and without the need to stop the torch.

In addition, power regulation can be associated with a temperature regulation of the environment in which the torch works. The means for controlling power regulation can then also be used as means for control the temperature regulation.

• une première boucle, de régulation en puissance,
• une seconde boucle, de régulation en température.

The invention therefore also relates to a system for regulating a plasma torch, with two nested loops:

• a first loop, of power regulation,
• a second loop, for temperature regulation.

Preferably, the means for controlling the regulation of the temperature comprise means for producing a signal for controlling the variation of the power of the torch as a function of an operating temperature T of the device in which the torch is placed and of the inertia (C _P ) of the device.

The invention also provides various means of monitoring of the system constituted by the torch and its environment. The torch can, in fact, be coupled to a very expensive device, such as for example a blast furnace or a foundry cupola or a furnace waste treatment. A defect in one of the easements torch can have dire consequences not only on the torch itself, but also on all the device located downstream.

Very close monitoring of the various easements that allow the torch to operate is therefore sometimes necessary.

To this end, the steering system of the torch may include means for sending to an operator interface for warning signals or allowing to send a stop signal operation upon the occurrence of faults fluid supply means or means power supply to the plasma torch. Of preferably a stop signal is sent before a signal alert.

Brief description of the figures

• la figure 1 représente schématiquement une torche à plasma,
• la figure 2 représente schématiquement une torche et ses systèmes de régulation et d'alimentation en fluide et en électricité,
• La figure 3 représente un exemple des abaques de fonctionnement d'une torche à plasma de 800 kW,
• la figure 4 représente un exemple de l'évolution de la tension optimale d'une torche à plasma, en fonction de sa puissance,
• la figure 5 représente des étapes d'un procédé de régulation en puissance selon l'invention,
• la figure 6 représente des étapes d'un procédé de régulation en puissance selon l'invention, en régime de rampe,
• la figure 7 représente des étapes d'un procédé de régulation en puissance selon l'invention, en régime permanent,
• la figure 8 représente l'évolution temporelle de la puissance d'une torche à plasma régulée conformément à la présente invention,
• La figure 9 représente l'évolution temporelle de la température de consigne et de la température d'un dispositif dans lequel est utilisé la torche,
• la figure 10 représente des étapes d'un procédé de régulation en température selon l'invention,
• la figure 11 représente schématiquement un circuit de refroidissement d'un système de torche selon l'invention,
• la figure 12 représente schématiquement un circuit d'alimentation en gaz plasmagène d'un système de torche selon l'invention,
• la figure 13 représente schématiquement un circuit hydraulique du starter d'une torche à plasma,
• la figure 14 représente schématiquement un circuit d'alimentation électrique d'un système de torche selon l'invention,
• la figure 15 représente une chaíne d'asservissement d'un système de torche selon l'invention.

In any case, the characteristics and advantages of the invention will appear better in the light of the description which follows. This description relates to the exemplary embodiments, given by way of explanation and without limitation, with reference to the appended drawings in which:

• FIG. 1 schematically represents a plasma torch,
• FIG. 2 schematically represents a torch and its systems for regulating and supplying fluid and electricity,
• FIG. 3 represents an example of the operating charts of an 800 kW plasma torch,
• FIG. 4 represents an example of the evolution of the optimal voltage of a plasma torch, as a function of its power,
• FIG. 5 represents steps of a power regulation method according to the invention,
• FIG. 6 represents steps of a power regulation method according to the invention, in ramp mode,
• FIG. 7 represents steps of a power regulation method according to the invention, in steady state,
• FIG. 8 represents the time evolution of the power of a plasma torch regulated in accordance with the present invention,
• FIG. 9 represents the time evolution of the set temperature and the temperature of a device in which the torch is used,
• FIG. 10 represents steps of a temperature regulation method according to the invention,
• FIG. 11 schematically represents a cooling circuit of a torch system according to the invention,
• FIG. 12 diagrammatically represents a plasma gas supply circuit for a torch system according to the invention,
• FIG. 13 schematically represents a hydraulic circuit of the choke of a plasma torch,
• FIG. 14 schematically represents an electrical supply circuit of a torch system according to the invention,
• Figure 15 shows a control chain of a torch system according to the invention.

Detailed description of embodiments of the invention

• deux électrodes tubulaires 2, 4 (amont et aval) entre lesquelles s'établit un arc électrique 18,
• une chambre 6 d'injection de gaz en vortex, située entre les deux électrodes 2 et 4,
• une bobine de champ 8, placé autour de l'électrode amont 2 et destinée à mettre en rotation le pied d'arc 20,
• un dispositif 10 d'amorçage de l'arc (starter) ; un tel dispositif est décrit par exemple dans la demande FR-89 14677,
• des équipements annexes de refroidissement, de raccordement, de protection et de maintien qui seront décrits plus loin de manière plus détaillée.

A plasma torch which can be used in the context of the present invention comprises the following elements, illustrated in FIG. 1:

• two tubular electrodes 2, 4 (upstream and downstream) between which an electric arc 18 is established,
• a vortex gas injection chamber 6, located between the two electrodes 2 and 4,
• a field coil 8, placed around the upstream electrode 2 and intended to rotate the arc foot 20,
• a device 10 for striking the arc (choke); such a device is described for example in application FR-89 14677,
• additional cooling, connection, protection and maintenance equipment which will be described in more detail below.

During operation of the torch, the air plasmagen is injected through the injection chamber 6, located between the electrodes, and is evacuated through of the downstream electrode 4.

The electric arc is then created by the establishment of the arc current and by the recoil synchronized with choke 10, which previously maintained short circuit the upstream electrode 2 and the electrode downstream 4.

At the moment of start-up, this short-circuit arc has the effect of locally overheating the air plasma and make it electrically conductive. The electric arc thus becomes a self-sustaining phenomenon.

Air, brought to very high temperature by the arc electric, constitutes the plasma jet which is projected outside the torch.

Due to the high temperatures prevailing in arc feet 20, the electrodes are cooled by a water circulation whose inlet and outlet are designated in Figure 1 by the references 14 and 16 for the downstream electrode 4 and 24 and 26 for the electrode upstream 2. This water is demineralized in order to maintain sufficient electrical isolation in the torch.

The life of the torch is improved by rotating and moving longitudinally the upstream and downstream arc feet in the electrodes so to avoid the melting of the material and to distribute the wear material on the largest possible surface. This action is carried out in the upstream electrode at field coil 8 which can be powered in series with the direct current of the arc or have a separate power supply. In the downstream electrode, the foot arc is rotated by the swirl effect air injected into a vortex.

• des moyens 30 d'alimentation électrique du système torche, commandés par des moyens 34 de contrôle (voir ci-dessous),
• des moyens 32 d'alimentation en fluide, qui comprennent un circuit d'eau de refroidissement de la torche,
• un circuit 33 d'air ou de gaz plasmagène,
• un circuit d'huile pour commander le starter d'amorçage 10,
• une vanne 29 qui règle l'admission de gaz plasmagène dans la torche,
• une interface opérateur 38 (ou calculateur superviseur),
• des moyens 34 de contrôle à programme, par exemple un automate, pour le pilotage de la torche 1. Un opérateur, par le calculateur superviseur de procédé 38 peut introduire dans les moyens de contrôle 34 des valeurs de consigne désirées, par exemple, des valeurs de consigne pour la puissance électrique, la puissance thermique et la température à laquelle se déroule un procédé entretenu par la torche 1.

As illustrated in Figure 2, the torch can be implemented with the assistance of the following subsystems which will be detailed later:

• means 30 for supplying electrical power to the torch system, controlled by control means 34 (see below),
• means 32 for supplying fluid, which comprise a circuit for cooling the torch,
• an air or plasma gas circuit 33,
• an oil circuit for controlling the priming starter 10,
• a valve 29 which regulates the admission of plasma gas into the torch,
• an operator interface 38 (or supervisor computer),
• means 34 of program control, for example an automaton, for piloting the torch 1. An operator, by the process supervisor computer 38 can introduce into the control means 34 desired set values, for example, values setpoint for electrical power, thermal power and the temperature at which a process maintained by torch 1 takes place.

The regulation and control programs of the torch are loaded in the industrial automat 34. This essentially comprises a unit central and input / output cards. It is programmed from a personal computer (PC). AT this end for example the constructor of the controller provides software to create a binary program in the PLC. The dialogue with the automaton is carried out via an exchange table, or memory area, by a supervision device. From the outside, the supervision (PC) sends messages at the exchange table. The machine comes to read the state of the table and puts the system (for example: a cooling circuit pump) compliance with memory or exchange table. The automatic device provided in the context of this invention can for example work with a cycle between approximately 10 ms and 100 ms (speed of reaction). Preferably, a cycle is used fast, around 10 ms.

PLC 34 sends control signals via links 41, 43, 53.

• Comme exposé par la suite, le pilotage de la torche incorpore une régulation de la puissance électrique qui lui est fournie, tout en essayant de maintenir la tension entre les électrodes à une valeur optimale.

The means 34 can also incorporate safety devices making it possible to alert an operator and / or to stop the operation of the torch when certain faults in the electrical supply means 30 or in the fluid supply means 32 occur. .

• As explained below, the piloting of the torch incorporates a regulation of the electric power supplied to it, while trying to maintain the voltage between the electrodes at an optimal value.

To this end, sensors 39, 40 make it possible to measure the voltage and current supplied to electrodes 2, 4 of the torch. The sizes supplied by these sensors are digitalized and allow calculate the actual power at which it operates the torch.

Likewise, a temperature sensor 42 can be intended to measure the temperature at which takes place a process maintained by the torch 1.

• de la géométrie de la torche,
• des forces aérodynamiques dues au vortex,
• des forces magnétiques dues à la bobine de champ.

The operation of a plasma torch can be described using arc voltage curves, as a function of the arc current, for given flow rates of plasma gas. We obtain a network of curves, or network of operating points, which is a function:

• the geometry of the torch,
• aerodynamic forces due to the vortex,
• magnetic forces due to the field coil.

This network of operating points is therefore unique for each type of torch.

An example of an abacus (isodebit curves) of operating points is given in figure 3, for an 800 kW power torch. In Figure 3, the curves I, II, III, IV correspond respectively to plasma gas flow rates of 10g / s, 15g / s, 20g / s, 30g / s. The other curves correspond to flow rates then increasing from 10g / s to 10g / s (40g / s, 50g / s, ...).

• le courant d'arc I,
• le débit de gaz plasmagène Q,
• la tension d'arc U qui exprime, ou traduit, sensiblement la longueur de l'arc.

Consequently, each type of torch has an operating range characterized by the following specific parameters:

• the arc current I,
• the flow of plasma gas Q,
• the arc voltage U which expresses, or translates, substantially the length of the arc.

In order to control the torch, it it is therefore possible to choose one of these two parameters as control parameter. In particular, I and Q are very good control parameters adapted, the voltage U arising from the chosen values by these parameters.

• l'arc ne s'accroche pas sur le nez de la torche,
• la tension ne dépasse pas la tension maximum permise par l'alimentation électrique,
• l'arc emplit un maximum de volume de l'électrode aval.

For optimum torch operation, the voltage value follows a curve U = f (P), where P is the power of the torch. Such a curve is established experimentally by ensuring that:

• the arc does not catch on the nose of the torch,
• the voltage does not exceed the maximum voltage allowed by the power supply,
• the arc fills a maximum volume of the downstream electrode.

The _optimal U = f (P) curve is obtained by experimentally establishing the Q = f (I) charts with constant flow rate, of the type given in Figure 3 and discussed above. This curve is loaded into the exchange table of the controller 34.

For each power value, the optimum operating point associating the length arc, efficiency and enthalpy.

A power P and a voltage U correspond to each point concerned. The combination of the power and the voltage of the selected points gives the _optimal U curve = f (P). An example of such a curve is given in FIG. 4 (curve C ₁ ).

The operation along the curve C ₁ is optimum, but other operating regimes are possible. Indeed, the curve C ₁ corresponds to the case where the torch operates with maximum efficiency. From a point on the curve C ₁ , a variation in the value of the voltage and / or of the electric power results in a reduction in the operating efficiency.

• la zone 1, située au-dessus de la courbe C₁ : dans cette zone, l'arc sort de l'électrode aval et devient trop long. Il est exclu de pouvoir travailler dans cette zone,
• la zone 2, située sous la courbe C₂ : le fonctionnement de la torche est instable, la tension et la résistivité sont trop faibles,
• la zone 3, située entre les deux courbes : le fonctionnement est possible, avec un rendement variable ; le rendement est optimal sur la courbe C₁ et il diminue lorsque les paramètres de fonctionnement éloignent le point de fonctionnement de la courbe C₁ pour l'approcher de la courbe C₂. Ceci correspond alors au cas où l'enthalpie du gaz s'accroít. Un concepteur peut choisir, pour une raison ou pour une autre, de faire fonctionner la torche le long d'une courbe située entre C₁ et C₂. Dans ce cas, il remplace, dans la table d'échange de l'automate 34, la courbe déjà introduite par la nouvelle courbe.

In FIG. 4, a second curve C ₂ represents the lower limit of the possible operating zone of the torch. These two curves in fact define three zones in the plane (P, U):

• zone 1, located above the curve C ₁ : in this zone, the arc leaves the downstream electrode and becomes too long. It is excluded to be able to work in this area,
• zone 2, located under curve C ₂ : the operation of the torch is unstable, the voltage and resistivity are too low,
• zone 3, located between the two curves: operation is possible, with variable efficiency; the yield is optimal on the curve C ₁ and it decreases when the operating parameters move the operating point away from the curve C ₁ to approach it of the curve C ₂ . This then corresponds to the case where the enthalpy of the gas increases. A designer may choose, for one reason or another, to operate the torch along a curve between C ₁ and C ₂ . In this case, it replaces, in the exchange table of the controller 34, the curve already introduced by the new curve.

The curve C ₁ constitutes an operating objective of the torch, to be achieved. To this end, the arc current I and air flow Q values are varied so as to vary the arc voltage U. The variations in current I and in voltage U cause variations in power. P = UI We can therefore say that the _optimal U = f (P) function described above follows from the torch transfer function U = F (I, Q). The latter reflects the fact that the input variables of the torch regulation system are the current I and the flow rate Q, the output variable being the voltage U.

• une augmentation du débit d'air Q entraíne une augmentation de la tension U et une augmentation de la puissance P : en effet, une augmentation du débit d'air entraíne une diminution de la température de l'air, et une augmentation de sa résistivité,
• une diminution du débit d'air Q entraíne une diminution de la tension U et une diminution de la puissance P,
• une augmentation du courant d'arc I entraíne une diminution de la tension U et une augmentation de la puissance P : en effet, une augmentation du courant d'arc entraíne une augmentation de la température du gaz plasmagène, donc une diminution de sa résistivité ;
• une diminution du courant d'arc I entraíne une augmentation de la tension U et une diminution de la puissance P.

The regulation of the torch is based on the following principles, which arise from the analysis made above of the characteristics of a plasma torch:

• an increase in the air flow Q causes an increase in the voltage U and an increase in the power P: in fact, an increase in the air flow causes a decrease in the air temperature, and an increase in its resistivity ,
• a decrease in the air flow Q causes a decrease in the voltage U and a decrease in the power P,
• an increase in the arc current I causes a decrease in the voltage U and an increase in the power P: in fact, an increase in the arc current results in an increase in the temperature of the plasma gas, therefore a decrease in its resistivity;
• a decrease in the arc current I leads to an increase in the voltage U and a decrease in the power P.

The principle of power regulation according to the present invention will now be described in more detail.

Before starting the torch, an operator introduces a power setpoint into PLC 34 CPUIS. By default, the controller 34 sets the setpoint at the same value as the previous setpoint.

At first, the power of the torch increases until reaching the power setpoint (this is the operation in ramp mode).

Second, the power of torch is stabilized around the power of setpoint (this is operation in steady state).

Measurements of the arc voltage U and of the arc current I are made at each cycle of the regulation process using voltage measurement means 39 and current measurement means 40 (FIG. 2). These quantities make it possible to calculate the real electrical power of the torch P _r = IU

The regulation then consists in modifying the setpoints for air flow Q and arc current I to approach the value P _r , measured, of CPUIS, with an optimal arc voltage (U _optimal ) which depends on the instantaneous power. real P _r .

As we saw earlier, the _optimal U = f (P) abacus is obtained from the torch characterization tests. This chart is therefore introduced beforehand by an operator into the memory means of the automaton 34.

• calcul de la puissance électrique réelle P_r,
• détermination de U_optimal,
• calcul de l'écart entre la consigne de puissance CPUIS et P_r : ΔP=|CPUIS-P_r|,
• une comparaison de ΔP et de ΔP_ra, où ΔP_ra est un seuil préalablement fixé par l'opérateur, à partir duquel on considère que la puissance réelle a atteint la valeur de consigne de puissance :
  • si ΔP≥ΔP_ra, le procédé reste ou passe en régime de rampe,
  • si ΔP≤ΔP_ra, le procédé reste ou passe en régime permanent.

At each cycle of the regulation process, the following operations are carried out:

• calculation of the real electrical power P _r ,
• determination of _optimal U,
• calculation of the difference between the power setpoint CPUIS and P _r : ΔP = | CPUIS-P _r |,
• a comparison of ΔP and ΔP _ra , where ΔP _ra is a threshold previously set by the operator, from which it is considered that the real power has reached the power setpoint:
  • if ΔP≥ΔP _ra , the process remains or goes into ramp mode,
  • if ΔP≤ΔP _ra , the process remains or goes into steady state.

• l'étape consistant à vérifier que les consignes de débit d'air Q et de courant d'arc I sont bien comprises entre des valeurs limites Q_max, Q_min et I_max, I_min.
• l'étape consistant à régler les consignes de courant et de débit aux valeurs limites, si elles ne sont pas entre les valeurs limites.

Other operating steps of the process can be provided, in particular:

• the step of verifying that the air flow Q and arc current I setpoints are indeed between limit values Q _max , Q _min and I _max , I _min .
• the step of setting the current and flow setpoints to the limit values, if they are not between the limit values.

Figure 5 is a flowchart of the power regulation according to the present invention.

Figure 6 shows a flowchart of the operation in ramp mode of the regulation according to the present invention.

This diet allows you to quickly reach the CPUIS value, either when the torch starts, or when the CPUIS setpoint is changed at during torch operation.

During this regime, the values of Q and I are incremented (according to first increments of ΔQ ₁ and ΔI ₁ ), with a periodicity DT ₁ , according to a slope of rise or fall in power.

• si P_r≤CPUIS, on cherche à augmenter la puissance de la torche. On peut donc accroítre I de ΔI₁ et, si U≤U_optimal, on peut également incrémenter Q de ΔQ₁,
• si P_r≥CPUIS, on cherche à diminuer la puissance de la torche. On peut donc diminuer le débit d'air Q de ΔQ₁ et, si U≤U_optimal, diminuer le courant d'arc I de ΔI₁.

For each time interval DT ₁ , the real power P _r is measured:

• if P _r ≤CPUIS, we seek to increase the power of the torch. We can therefore increase I by ΔI ₁ and, if U≤U _optimal , we can also increment Q by ΔQ ₁ ,
• if P _r ≥CPUIS, we seek to reduce the power of the torch. We can therefore reduce the air flow Q by ΔQ ₁ and, if U≤U _optimal , reduce the arc current I by ΔI ₁ .

This operating regime makes it possible to increase or decrease the power of the torch while remaining as close as possible to the optimal voltage U _optimal When ΔP becomes less than ΔP _ra , the ramp regime is abandoned in favor of the permanent regime.

Steady-state operation consists in maintaining the real power at the value of the set power, when this is reached, with a tolerance ΔP _ra , and this while keeping the optimal arc voltage U _optimal . To this end, the values of the air flow Q and of the arc current I are incremented or decremented with increment or step values, ΔQ ₂ , ΔI ₂ , and this with a periodicity DT2 (for example: DT ₂ = DT ₁ ).

• si U<U_optimal et P_r<CPUIS :
  • si Q<Q_max (débit maximum du gaz plasmagène) : Q est incrémenté de ΔQ₂,
  • sinon : I est incrémenté de ΔI₂

After each time increment DT ₂ :

• if U <U _optimal and P _r <CPUIS:
  • if Q <Q _max (maximum plasma gas flow rate): Q is incremented by ΔQ ₂ ,
  • otherwise: I is incremented by ΔI ₂

• si U<U_optimal et P_r>CPUIS :
  • si I>I_min : le courant d'arc est décrémenté de ΔI₂,
  • sinon, le débit d'air Q est décrémenté de ΔQ₂.

In the first case, the increment of the air flow causes an increase in voltage and power. In the second case, the increment of the arc current causes a reduction in the voltage, despite the objective set to keep the voltage at an optimal value: this means that, temporarily, the process favors power at the expense of voltage , and therefore power at the expense of efficiency. This loss of yield is compensated during the following process cycles.

• if U <U _optimal and P _r > CPUIS:
  • if I> I _min : the arc current is decremented by ΔI ₂ ,
  • otherwise, the air flow Q is decremented by ΔQ ₂ .

• si U≥U_optimal et P_r≥CPUIS, le débit d'air est décrémenté de ΔQ₂.
• si U≥U_optimal et P_r≤CPUIS, le courant est incrémenté de la valeur ΔI₂.

In the latter case, the decrease in air flow results in a loss of voltage and efficiency. But, here again, this loss is temporary and is compensated during the following loops of the regulation process.

• if U≥U _optimal and P _r ≥CPUIS, the air flow is decremented by ΔQ ₂ .
• if U≥U _optimal and P _r ≤CPUIS, the current is incremented by the value ΔI ₂ .

Figure 7 is a flow chart of the scheme regulation process according to the invention.

The torch control system remains in permanent operation as long as a modification of the CPUIS power setpoint does not intervene.

When such a modification occurs, introduced for example by the operator into the automaton 34, ΔP becomes greater than ΔP _ra , and the process returns to ramp mode.

Thus, as illustrated in FIG. 8, the method according to the invention makes it possible to change the real power of the torch as a function of time, while remaining as close as possible to the optimal operating conditions or to the conditions chosen by the operator. In FIG. 8, the power increases first according to a ramp regime, to reach a setpoint CPUIS ₁ at the instant t ₁ . This setpoint is maintained until time t ' ₁ , where the operator modifies the power setpoint in CPUIS ₂ : the operation is then again operation in ramp mode (decreasing) until time t ₂ . Then, between t ₂ and t ' ₂ , steady state operation makes it possible to maintain the power substantially at CPUIS ₂ . At t ₂ , a new power setpoint CPUIS ₃ is introduced by the operator. The process then returns to ramp mode to reach this new setpoint, until time t ₃ . From t ₃ , the torch works again in steady state. Such operation can be continued as long as necessary.

The torch regulation process, described above, makes the power of the torch almost independent of internal or external factors (disturbances) which can influence the parameters of control I and Q. The state of wear of the electrodes, the pressure of the plasma gas, its composition are parameters which are likely to vary during the torch operation and which could therefore influence its performance and derive the power supplied.

In fact, the regulatory system according to the This invention avoids this problem. By example, if the humidity of the plasma gas increases, it this results in a decrease in the tension between the electrodes (gas resistivity decreases). According to process described above, this results in a decrease current and / or increased flow, which tend to bring the voltage back to its optimal value. The influence of humidity is therefore compensated automatically. The same applies to the influence of other disturbances.

• des moyens pour mémoriser une courbe de la tension d'arc de la torche, dite courbe de tension optimale, en fonction de la puissance électrique réelle fournie à la torche,
• des moyens pour commander une régulation de la puissance de la torche, et fonctionnant :
  • selon un premier régime, dit régime de rampe, afin que la puissance réelle atteigne une valeur dite valeur de consigne de la puissance, avec une tension d'arc égale à la tension optimale,
  • selon un second régime, dit régime permanent, afin de stabiliser la puissance réelle autour de la valeur de consigne, avec une tension d'arc égale à la tension optimale.

According to the invention, the torch control system therefore comprises:

• means for memorizing a curve of the arc voltage of the torch, known as the optimal voltage curve, as a function of the real electric power supplied to the torch,
• means for controlling regulation of the power of the torch, and operating:
  • according to a first regime, called the ramp regime, so that the real power reaches a value called the power reference value, with an arc voltage equal to the optimal voltage,
  • according to a second regime, called permanent regime, in order to stabilize the real power around the set value, with an arc voltage equal to the optimal voltage.

The power regulation process described above only involves the torch itself. Such a process does not take into account the environment in which the torch operates. The torch works in a device or environment to which it brings energy, this device or this environment to be brought to a temperature given, for example constant or cyclic. The contribution required for temperature maintenance can also be variable depending on the state in which is the device or the environment. If, by example, the torch is used with or in an oven, it may be necessary to vary the intake thermal during oven loading phases, or oven temperature homogenization phases.

In addition to the power regulation system described above, the invention allows temperature regulation of the environment in which the torch is placed. This temperature regulation, based on the modulation of the power of the torch, is implemented to bring the environment to a set temperature CT _f and maintain it at this temperature. This temperature regulation is a second level regulation which is superimposed on the power regulation, which is always active.

• la consigne de température finale CT_f,
• la pente de montée ou de descente de la température C_P=ΔT/Δt : cette grandeur traduit le fait que la température de l'environnement de la torche varie avec une vitesse limitée. En fait, cette grandeur C_P est à déterminer expérimentalement et découle directement de la fonction de transfert du four. Par la connaissance de l'environnement, de la manière dont il doit travailler, et des essais de caractérisation, on peut connaítre les valeurs que l'on peut donner à C_p, en fonction de la puissance de la torche. Si C_p a une valeur trop grande, la puissance de la torche atteint sa valeur maximum trop rapidement, sans que la pente de montée en température de l'environnement soit respectée. Si la valeur de C_P est trop faible, la torche reste à trop faible puissance.

The temperature regulation parameters are as follows:

• the final temperature setpoint CT _f ,
• the slope of rise or fall of the temperature C _P = ΔT / Δt: this quantity reflects the fact that the temperature of the environment of the torch varies with a limited speed. In fact, this quantity C _P is to be determined experimentally and follows directly from the transfer function of the furnace. By knowing the environment, how it should work, and characterization tests, we can know the values that we can give to C _p , depending on the power of the torch. If C _p is too large, the power of the torch reaches its maximum value too quickly, without the slope of the rise in temperature of the environment being respected. If the value of C _P is too low, the torch remains at too low power.

The temperature regulation consists in incrementing or decrementing the power of the torch by a certain number of times an increment ΔP, in order to reach the temperature of the final CT _f oven, respecting the slope C _P.

During each cycle of the temperature regulation process according to the invention, the temperature of the environment is measured (using the temperature sensor 42, FIG. 2). This value T _m is memorized, as is the value of the temperature T _m-1 of the previous cycle.

In addition, the automaton knows the value of the initial temperature T ₀ (temperature at the start of the regulation) and can calculate the instantaneous set temperature T _C : T _C = T ₀ ± C _p xΔT, where ΔT is the increment time (or time step) of the cycle.

At each cycle, there is therefore the instantaneous setpoint temperature T _C , the actual temperature T _m , and the actual slope PEN _r = (T _m -T _m-1 ) / ΔT.

This last quantity is the effective slope temperature rise or fall in the oven, in ° C / h, for cycle m.

• si T_m<T_C-ΔT : la puissance est incrémentée de 2ΔP,
• si T_m>T_C+ΔT : la puissance est décrémentée de 2ΔP,
• si PEN_r<C_P-ΔPE : la puissance est incrémentée de ΔP,
• si PEN_r>C_P+ΔPE : la puissance est décrémentée de ΔP.

Let ΔT be the temperature difference tolerance between T _C and T _m , and APE the slope difference tolerance between the actual slope PEN _r and C _P. So :

• if T _m <T _C -ΔT: the power is increased by 2ΔP,
• if T _m > T _C + ΔT: the power is decremented by 2ΔP,
• if PEN _r <C _P -ΔPE: the power is increased by ΔP,
• if PEN _r > C _P + ΔPE: the power is decremented by ΔP.

For such a temperature regulation method, the evolution of the temperature as a function of time is represented diagrammatically in FIG. 9. The straight line of slope Cp represents the evolution of the set temperature of the environment. Around each of the instants t ₁ , t ₂ , ... t ₇ the actual temperature and the actual temperature slope are respectively measured and calculated. For each of these instants, the corresponding value of increment or decrement, in power, is plotted on the graph. Thus, around time t ₁ , the temperature difference, compared to the instantaneous setpoint, is greater than ΔT, which leads to a power increment of 2ΔP; moreover, the difference between the real slope and C _P results in a power increment of ΔP, hence a total power increment of 3ΔP.

• CT_f : même valeur que la consigne précédente,
• C_p : même valeur que la consigne précédente,
• P, ΔT, ΔPE : valeurs données selon les caractéristiques de l'ensemble constitué par la torche et son environnement (par exemple la torche et le four).
• CT_I (consigne de température initiale) et C_p ont des valeurs initiales que l'opérateur peut retrouver en demandant une initialisation.

FIG. 10 is a flow diagram which schematically represents the succession of steps of the temperature control method according to the present invention. For example, T _m is measured with a periodicity of 60 seconds. In addition, you can choose to give the parameters the following default values:

• CT _f : same value as the previous setpoint,
• C _p : same value as the previous setpoint,
• P, ΔT, ΔPE: values given according to the characteristics of the assembly constituted by the torch and its environment (for example the torch and the furnace).
• CT _I (initial temperature setpoint) and C _p have initial values that the operator can find by requesting an initialization.

Two complementary aspects of a regulation of a torch have been described above: the power regulation and regulation in temperature. The temperature regulation makes use of power regulation. But in some applications, power regulation can be performed without temperature regulation. When the two are used, a double regulation is obtained of the system constituted by the plasma torch.

The means 32 for supplying the torch with fluid will now be described.

Figure 11 is a diagram of circuit 32 of torch cooling.

The plasma torch is continuously cooled by circulation of demineralized water under pressure, in its inner part, around the upstream electrodes and downstream, around the field coil and in its part outside, around the downstream outer envelope. This cooling water circulation in the torch is provided by a pump 48 and allows energy to be dissipated transmitted to the walls by the electric arc, as well as by the temperature of the device or the environment in which is located the downstream end of the torch.

The torch cooling water is demineralized to guarantee electrical isolation of various live parts of the torch. Of preferably, the resistivity of the water is checked by permanently using a resistivity sensor connected to PLC 34 (Figure 2). Automatic regeneration of part of the water flowing in the torch maintains the resistivity above a minimum threshold.

A solenoid valve 50 controls the water intake 52 in the demineralized water circuit consisting of demineralization cartridges 54 and reservoir 46.

A circuit 60 for recycling water from demineralization helps maintain the quality of demineralized water passing through the torch. This circuit, bypass on the tank, passes part of water in the 54 resin cartridges demineralization and reinjects it into the reservoir 46, when the circulation of water in the torch is activated.

Demineralization is therefore done automatically by a permanent bypass of the water circuit, without the intervention of the automaton.

The recycling rate is adjusted manually by a valve.

A pressure sensor 47 makes it possible to monitor pressurization of the cooling circuit. If the pressure becomes below a fault threshold, there electric torch stop.

The tank filling cycle 46 allows permanently obtain a supply of demineralized water sufficient to ensure optimum cooling of the torch in service. It automatically engages following a drop in water pressure (given by the tank pressure sensor) when this reaches the minimum threshold and stops when the threshold maximum is reached. The different thresholds are detected by comparison between the analog measurement of pressure and thresholds stored in the PLC. It is the latter who then orders the opening of the valve 50.

A level sensor 45 stops the cooling pump in the event of a major leak to prevent the pump from running dry.

The evacuation of the energy captured by the circuit cooling is provided by an exchanger (plate heat exchanger) 42 common with a water circuit secondary 44. The latter may include a air cooler operating on the principle of evaporation and form a closed loop or, more simply be open loop with a continuous flow lost water, depending on availability or choice of device installation site.

A circuit 56, comprising a valve 58, can be provided to provide emergency cooling. It is connected for example to the city network and brings therefore non-demineralized water with torch 1, which pollutes the water circuit. This device is intended for intervene only when the pumps are stopped and that the torch is still in the device in which it operates.

• une surveillance du remplissage du réservoir : si la durée de remplissage est trop longue, ou si le temps entre deux remplissage est trop important, l'automate 34 peut envoyer un message à l'opérateur ou émettre un signal d'alarme,
• une surveillance de la déminéralisation : des moyens peuvent être prévus, en combinaison avec le réservoir 46 ou le circuit 60, pour mesurer la résistivité de l'eau déminéralisée. Un signal est alors envoyé vers l'automate 34, où la résistivité mesurée est comparée à une, ou des, valeur(s) seuil. Un seuil de défaut et/ou un seuil d'alarme peuvent être prévus, pour lesquels :
  • si la résistivité mesurée est inférieure au seuil de défaut, la torche est arrêtée électriquement et une alarme est émise,
  • si la résistivité mesurée est inférieure au seuil alarme, une alarme est émise,
• une surveillance de la circulation d'eau : des capteurs permettent de mesurer le débit d'eau dans la torche et/ou le niveau d'eau dans la cuve et/ou la pression d'eau dans ce circuit et/ou les températures de l'eau en entrée et en sortie de la torche.

Various monitoring functions can optionally be provided in addition to the circuit described above, together or separately:

• monitoring the filling of the tank: if the filling time is too long, or if the time between two filling is too long, the automatic device 34 can send a message to the operator or issue an alarm signal,
• demineralization monitoring: means can be provided, in combination with the tank 46 or the circuit 60, to measure the resistivity of demineralized water. A signal is then sent to the controller 34, where the measured resistivity is compared with one or more threshold value (s). A fault threshold and / or an alarm threshold can be provided, for which:
  • if the resistivity measured is below the fault threshold, the torch is electrically stopped and an alarm is issued,
  • if the measured resistivity is below the alarm threshold, an alarm is emitted,
• water circulation monitoring: sensors measure the water flow in the torch and / or the water level in the tank and / or the water pressure in this circuit and / or the temperatures of the water entering and leaving the torch.

• une surveillance de la pompe 48 : lorsque celle-ci est à l'arrêt et que la torche est en position sur un site d'utilisation, une pompe 49 de secours est mise en marche sur commande de l'automate 34.

For flow, pressure and temperatures, alarm and / or fault thresholds can be provided, to which the PLC compares the measured values. The crossing of the alarm threshold causes the emission of an alarm signal, that of the fault threshold causes the torch to stop. For the water level, passing under a very low level causes the pumps and the torch to stop,

• monitoring of the pump 48: when the latter is stopped and the torch is in position at a site of use, a backup pump 49 is started on command from the automatic device 34.

• remplissage du circuit hydraulique et appoint d'eau brute,
• recyclage de déminéralisation de l'eau de refroidissement,
• circulation d'eau dans la torche,
• refroidissement de secours,
• réfrigération de l'eau, éventuellement.

Consequently, the controller 34 can be provided to monitor and control the following different functions:

• filling the hydraulic circuit and adding raw water,
• recycling of demineralization of cooling water,
• circulation of water in the torch,
• emergency cooling,
• water refrigeration, if necessary.

• par le recul automatique de la torche,
• par le circuit de secours 56 si le recul de la torche n'est pas validé,
• par l'envoi, à l'opérateur, d'une information d'Avarie Majeure, si le débit d'eau est encore insuffisant et que le recul de la torche n'est toujours pas validé.

Protection in the event of a power outage or pump shutdown can be provided:

• by automatic recoil of the torch,
• by the emergency circuit 56 if the reversing of the torch is not validated,
• by sending, to the operator, Major Damage information, if the water flow is still insufficient and the recoil of the torch is still not validated.

• le refroidissement de la torche est assuré lorsqu'elle est en fonctionnement, et tant qu'elle se trouve dans le dispositif (sous peine d'une fusion très rapide des électrodes et de sa partie aval).
• en cas de perte de refroidissement, lorsque la torche est dans le dispositif, des actions de secours sont prévues et générés par les moyens 34 de contrôle/commande, selon la configuration de l'installation et le type de cause :
• 1. mise en route automatique d'une pompe de secours,
• 2. recul automatique de la torche,
• 3. circulation d'eau brute de secours.

Operational safety can therefore ensure compliance with the following rules:

• the cooling of the torch is ensured when it is in operation, and as long as it is in the device (on pain of a very rapid fusion of the electrodes and of its downstream part).
• in the event of loss of cooling, when the torch is in the device, emergency actions are provided and generated by the control / command means 34, depending on the configuration of the installation and the type of cause:
• 1. automatic start-up of a backup pump,
• 2. automatic torch recoil,
• 3. emergency raw water circulation.

The operating parameters (pressure, flow, water temperature, resistivity) can be continuously measured and, in case of drift of one operator can be alerted before security actions are not required.

The means for generating and controlling the flow of plasma gas supplied to the torch will now be described, in conjunction with FIG. 12. The plasma gas can be air coming from an industrial air network, or from a compressor. The minimum available pressure should preferably be of the order of 6 bars, and the flow rate of 300 Nm ³ / h, or approximately 110 g / s, at a power of 800 kW.

At the outlet of compressor 62, the air is de-oiled, dried and filtered to about 1 / 10th of micrometer, using filtering means 64 and a drying device 66.

A buffer tank 68 creates an air reserve and avoids pressure fluctuations generated by the compressor upstream of the control valve 29.

A flow meter 70 makes it possible to measure the flow air sent to torch 1. This flow is controlled by the pilot valve, or regulation valve, 29 (Cf. figure 2). Preferably, it is the automaton 34 which ensures the starting and stopping of the drying, compressor, and opening and closing of the regulating valve 29. As soon as the torch is not no longer in position of withdrawal from its place of use, a minimum air flow is emitted in the torch to avoid internal pollution.

The flow meter 70 provides a measured value of the flow which can be compared, in the automaton 34, to one or more threshold values, for example a alarm threshold value and / or a threshold value default. When crossing the alarm threshold, a warning signal is sent to an operator. The crossing the fault threshold results in stopping the torch, dryer and compressor; valve 29 is then also closed, except for the case where the torch is still at its place of use, in which case a minimum air circulation value is maintained, this which prevents pollution of the torch by the environment.

Information on the value of flow air can also play a role, as we have already explained above, as part of the regulation in torch power. The regulation provided for in the framework of the present invention has the advantage an external disturbance on the air circuit (e.g. a change in air humidity, or a change in air pressure) does not cause a torch stop. The operator can be warned, but the regulating device according to the present invention allows to react and compensate for disturbances air flow.

Conversely, the gas flow is controlled in depending on the power, or possibly the required gas enthalpy, before being injected into the torch.

The torch starting device (or "starter") will now be described, in conjunction with FIG. 13, where it is designated by the reference 71.

It will be recalled beforehand that a device boot is described in application FR-89 14677. The choke device ensures maintenance under pressure of the actuator hydraulic circuit. In addition, it controls the advance and retreat of the cylinder start 2 (figure 1). It is this device which ensures striking the arc in the torch. Before priming, it is in the advanced position, the upstream electrode is at contact of the downstream electrode and creates a short circuit. At startup, during the establishment of the arc current, this cylinder quickly moves the electrode back upstream and "draws" the arc between the two electrodes.

In FIG. 13, the reference 74 designates a tank which contains the oil of the hydraulic circuit. A pump 76 causes part of the oil to rise in a double accumulator 78. The upper part of it contains air. When the pressure increases in the accumulator and reaches a high limit, the pressure switch 80 cuts the pump motor 76. The pressure switch 82 restarts the pump when the oil pressure reaches a low limit.

A pressure fault 84 pressure switch prohibited starting the torch if the oil pressure is not not sufficient.

A distributor 87 has a part 86 associated with the choke advance function and a part 88 associated with the choke recoil function. In FIG. 12, the distributor is in the position of recoil of the choke: the oil pressure is therefore directed towards the rear of the cylinder.

To each of the priming cylinder compartments is then associated with a flow restrictor 89-90, 91-92. Each has a non-return valve 89, 91 and a flow restrictor 90, 92. The limiters are mechanical control systems that allow oil to go to and from the cylinder.

The oil returns to the tank via an oil filter 93 (oil filter 10 µm). Finally, the reservoir 74 is equipped with a air 94.

The power supply means provide the supply of the field coil 8 (figure 1) and the arc 18 (Figure 1) either arranged in series, or separate, from a high voltage network.

The power supply means 30 are shown schematically in Figure 14. They include a high voltage power supply 100, a transformer 102 (usually two-phase) and a rectifier 104. They provide a supply of direct current to the torch electrodes and to the field coil. A smoothing choke 114 of a overvoltage 112 absorbs current fluctuations from the electric arc.

Arc rectifier 104 consists of essentially from Graetz bridges (e.g. 6 thyristors by bridge). Means 110, of the type fans, ensure circulation sufficient air in rectifier 104.

This is actually programmed by a current setpoint I _arc sent from the controller 34. The development of this setpoint has been described above in the context of the power regulation process of the torch.

Monitoring of faults in the means power supply is centralized at the level of rectifiers 104. Transmission of information on faults is carried out directly to the PLC 34.

Standard sensors allow measurement arc current and arc voltage values in torch 1.

Arc currents can be associated with alarm and fault thresholds (e.g. 50 amps for the alarm threshold and 100 amperes for the default). The crossing of these thresholds leads, in the first case, the emission of an alarm signal from arc current and, in the second case, stopping the torch.

For the arc voltage, three thresholds can be provided: a minimum threshold below which the voltage is too low, an alarm threshold and a threshold default. When the voltage drops below minimum threshold or higher than the alarm threshold, a corresponding alarm signal is sent by the PLC 34. When the voltage becomes greater than the threshold of fault, torch 1 is stopped.

The regulatory system of the invention is a system with two nested loops: a first loop concerns power regulation and a second loop concerns temperature regulation. Chain of the torch system is represented schematically in Figure 15.

The left column contains the setpoints T (temperature of the device or the environment of the torch), P (in kW, electric power supplied to the torch), I (in A, current) and Q (in Nm ³ / h, plasma gas flow).

A manual setpoint 120 allows the operator to select only the power regulation function. Furthermore, a setpoint 122 makes it possible to set the power to a minimum value P _minimum , for example in the case where the torch is used in an oven and where the latter is under overpressure.

Power regulation then takes place as described above (block 124 in Figure 15). We note that instructions 126, 128 may further be provided to block current I and flow Q at their fixed set value (in which case there is no longer power regulation). Disturbances 131, by example of air flow, are taken into account. The function F represents the transfer function of the torch.

The temperature regulation takes place, it also, as described above (block 132 in the figure 15). A difference ε between the measured temperature and the setpoint temperature changes the setpoint power according to P = g (T) (block 134). The G function (T = G (P)) represents the transfer function of the torch and oven.

Finally, the method can authorize or prevent the torch system operation according to the state of different easements (supply of plasma gas, cooling circuit, etc.) as already described above.

In general, the invention set out in this application is particularly well suitable for regulating and / or piloting a torch with plasma with a power greater than 100 kW, for example with a power equal to 800 kW, or 2MW or 4 MW.

Claims (16)

System for piloting a plasma torch (1), comprising: means (34) for storing a curve (C ₁ ) of the arc voltage of the torch, known as the optimal voltage curve, as a function of the real electric power supplied to the torch, means (124) for controlling regulation of the power of the torch, and operating: according to a first regime, known as the ramp regime, so that the real power reaches a value (CPUIS) called the power reference value, with an arc voltage which evolves, to within a margin of error, with the optimal voltage , according to a second regime, called permanent regime, in order to stabilize the real power around the set value (CPUIS), with an arc voltage equal, to within an error margin, to the optimal voltage. System for piloting a torch plasma according to claim 1, further comprising means to determine, according to the deviation between the value of the actual electrical power and the power setpoint, according to which two regimes the means of control of the regulation have to work. System for piloting a torch plasma according to one of claims 1 or 2, the means for controlling the electric power of the torch producing a signal of modification of the value of the arc current and / or the air flow in order to modify the values of the real power and the arc voltage. System for piloting a torch plasma according to one of claims 1 to 3, comprising further means (38) for changing the value of power setpoint when the control means operate in steady state. System according to one of claims 1 to 4, further comprising means (132) for controlling regulation of the temperature of a device to which the torch (1) provides energy. System according to claim 5, the means (124) to control regulation of the power of the torch being also used as means for control the temperature regulation of the device. System according to claim 5, the means (132) to control the temperature regulation of the device for controlling an increment or a decrease in torch power. System according to claim 5, the means (132) for controlling the temperature regulation comprising means for producing a control signal for varying the power of the torch as a function of an operating temperature T _f of the device in which is placed the torch and inertia (C _p ) of the device. System according to claim 5 or 8, the temperature control means producing a signal to increment or decrement the torch power according to, on the one hand, the difference between the actual temperature measured in the device and a instantaneous set temperature and, on the other hand, the difference between the rate of temperature change and the inertia of the device. System according to one of claims 1 to 9, further comprising means for sending warning signals to an operator interface (38) upon the occurrence of lack of means supply of fluids (32, 33, 71) or means power supply (30) to the plasma torch. System according to one of claims 1 to 10, further comprising means for sending a signal to stop torch operation when the occurrence of faults in the supply means fluids (32, 33, 71) or supply means electric (30) of the plasma torch. System according to one of claims 10 or 11, the means for supplying fluids comprising means (32) for circulating a fluid cooling of the torch and / or of the means (33) for circulating a plasma gas and / or means (71) to supply fluid to a starting cylinder of the torch. System according to one of claims 10 or 11, the means (32) for supplying fluid comprising means (54) for demineralizing a fluid cooling, means for monitoring the demineralization of the fluid and / or means for monitor the coolant flow in the torch and / or the fluid pressure and / or the temperature of the fluid entering and leaving the torch. System according to one of claims 10 or 11, the means (33) for supplying fluid further comprising means (70) for circulating a plasma gas and means for monitoring the flow of plasma gas sent into the torch. System according to one of claims 10 or 11, the fluid supply means comprising means (71) for supplying fluid to a cylinder torch start and means to monitor the fluid pressure transmitted to the cylinder. System according to one of claims 10 to 15, the power supply means (30) providing the torch with arc current and voltage arc and further comprising means (39, 40) for monitor this arc current and this arc voltage.

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