PatentDe  


Dokumentenidentifikation EP1305863 29.12.2005
EP-Veröffentlichungsnummer 0001305863
Titel ÜBERSPANNUNGSSCHUTZSYSTEM
Anmelder Koninklijke KPN N.V., Groningen, NL
Erfinder KOUWENHOVEN, Theodorus, Jacobus, NL-1312 SP Almere, NL;
HARTMANN, Henricus, Michiel, NL-7415 EK Deventer, NL;
KRUL, Frans, Teunis, NL-2552 CS The Hague, NL
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60115248
Vertragsstaaten AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE, TR
Sprache des Dokument EN
EP-Anmeldetag 09.07.2001
EP-Aktenzeichen 019671353
WO-Anmeldetag 09.07.2001
PCT-Aktenzeichen PCT/EP01/07884
WO-Veröffentlichungsnummer 0002009253
WO-Veröffentlichungsdatum 31.01.2002
EP-Offenlegungsdatum 02.05.2003
EP date of grant 23.11.2005
Veröffentlichungstag im Patentblatt 29.12.2005
IPC-Hauptklasse H02H 9/06

Beschreibung[en]
Background of the invention

The invention relates to a system for lightning and surge protection of objects.

In particular, the invention may be used as a system for lightning and surge protection for an object set up on a limited area, on the ground or on a building. Example of such an object comprise an installation provided with an antenna, e.g. a GSM base station. Surge protection devices for electrical power supplies are generally known.

The protection device according to the application may be used to protect against surge with a high energy content, such as surges caused by lightning or electromagnetic pulse (EMP). More in particular, the application relates to protection against surge caused by lightning strikes in a power supply for electrical equipment set up in objects, such as transmitter/receiver stations for radio traffic.

For such a protection device, in addition to a number of specific components and measures, one or more (preferably at least two) earth electrodes are employed for the purpose of deflecting the charge which is inherent in the surge and distributing it over the greatest possible area. It goes without saying that these earth electrodes must have the least possible resistance to the zero potential. It is, moreover, important that the ground area over which the charge of the lightning strike is to be distributed is at least of a minimum magnitude.

E.g, in the case of electrical power supplies for base stations for mobile telecommunication, such a minimum area is often not available because, for economic reasons, the area is preferably chosen to be no larger than necessary for the dimensions of the foot of the antenna mast. In the case that the object is positioned on top of a building, usually only a limited number of conductors with earth electrodes are used.

If the charge of a lightning or of EMP strikes the cabinet in which the power supply is housed or the metal frame to which the cabinet is attached, there is a danger of parasitic flash-over of the charge to the electrical conductors of the power supply. Since this charge is dissipated relatively poorly, the voltage in the power supply can rise to such an extent that flash-over can damage the components of the power supply, such as switches or cause failures of the power supply. Also, other equipment of the object, such as the equipment being supplied with power may be damaged.

That this voltage can be substantial can be understood from the fact that from a direct lightning strike a peak current of as much as 150 kA may arise, which must be deflected via an earth electrode having an impedance of 2.5 Ohm (this value being a standard value for earth electrodes, in practice this value may be higher or lower).

Momentarily, this may lead to voltages of over 100 kV. For such a peak voltage, a power supply for low voltage applications is not equipped.

Such a parasitic flash-over is prevented according to the state of the art by connecting surge protective devices, such as varistors or spark gaps, between the frame and each of the phases and between the frame and each of the neutral conductor of the power supply. The frame is connected directly to an earth connection, such as one or more earth electrodes. This way, parasitic flash-over from the part on which the strike occurs to one of the conductors is prevented.

In this known solution, however, it can not be prevented that in the power supply substantial damage occurs when a direct lightning strike occurs on the frame, which will be further explained in the detailed description. Here, it suffices to mention that this damage may comprise the burning of one or more components of the power supply caused by the very large currents. Moreover, mechanical damage may arise in the power supply as the large currents flowing through the conductors of each of the phase conductors and of the neutral conductor cause the connecting conductors to be pulled from the connection points, through the electromagnetic fields caused by the large currents, as a result of which an interruption in the current flow occurs.

It need not be mentioned that, also because of the earlier mentioned periphery arrangement of the power supply and the less proper accessibility thereof, repair of the damage will take a lot of time. As a result, the installation powered by the power supply will be out of service for a longer period of time, which leads to a higher risk of operational damage.

European patent application EP-A-0 128 344 describes an arrangement for surge arresters in a high voltage transformer. In this arrangement, surge arresters are connected between each phase conductor and the neutral conductor, and also between the neutral conductor and an earth electrode. The surge arresters are all of the same type. Additionally, a capacitor is connected between the neutral conductor and a second earth electrode. This results in a protection of the transformer against too high voltage peaks, in which the capacitor control the dynamic behavior of the surge arresters. The surge arresters are usually chosen to be spark gap elements, as these can be used in high voltage applications. The arrangement described is meant specifically for protection of the high voltage transformer.

A disadvantage of the use of spark gap elements or spark gaps connected between the phase conductors and the neutral conductor is that a rest voltage results which is poorly defined and usually too large. Furthermore, spark gaps will keep an undefined rest voltage, dependent on the rise time of the lightning pulse, which may be 2.5 to 4 kV, which is too high for low voltage equipment. Also, the spark gap elements cause a short circuit and thus a net following current, which almost certainly results in breakdown of the fuses (of the electricity provider). Breakdown of the fuses results in operational down time of the equipment supplied by the transformer.

In a conference paper "Bliksem Seminar 1999". 1999, page 49, figure 17, from which the claims are delimited, a lightning protective device is shown that comprises a first protective device that is the same as the lightning protection device as shown in EP-A-0 128 344. However, this figure 17 also shows an additional protective device that comprises varistors between the three phase conductors and the neutral conductor, and a spark gap between the neutral conductor and an earth electrode. This additional protective device is arranged downstream from the first protective device, seen in a direction from the mains. The first protective device is disclosed to comprise components of a lightning current capability of a class B, corresponding to a lightning protection class of > 50 kA (10/350 µs), > 75 kA (10/350 µs), or > 100 kA (10/350 µs). The additional protective device is disclosed to be an overvoltage protection device with class C components. Class C components have a surge current capacity of > 20 kA (8/20 µs).

The present invention seeks to provide a system for surge protection for use in low voltage applications, which does not have the disadvantages of the known systems described above. The present invention also seeks to provide a solution to the problem that the power supply defined in the preamble above, has such a limited deflection path in earth in order to deflect the charge of the strike, that the peak voltage occuring is relatively high and decreases relatively slowly.

Summary of the invention

According to the present invention, a system for surge protection is provided as claimed in claim 1.

The surge protective device of the first type is primarily meant to provide a well defined safety level (maximum voltage over ist connection leads) and the surge protection device of the second type is primarily meant to arrest or deflect high currents.

By using different types of surge arresters between the phase conductors and the neutral conductor and between the neutral conductor and the earth electrode, the system provides a very efficient surge protection, e.g. caused by lightning strike on an object. The solution of the present invention has as one insight whereon the invention is based that the frontal edge of the lightning current flows through the earth electrodes and the other components of the lightning current flow through the connected conductors (i.e. the supply conductors and other conductors). It is believed that this phenomenon occurs because of the limited ground surface to which the earth electrode is connected. The neutral conductor between the power supply unit and transformer to which the power supply unit is connected, is not connected to a self-induction while the phase conductors are connected to a self-induction. The self-induction may be a transformer coil or winding, or a coil of a kilo-watt hour meter. This causes that the current through the neutral conductor will be larger than the current through the phase conductors.

The surge protective device of the first type is a voltage dependent resistor, or varistor. The resistance value of such an element abruptly decreases when the voltage over the element passes a preset voltage value. The surge protective device of the second type is a spark gap element, or spark gap. These elements cause a discharge to occur when the voltage across its terminals increases above a preset value, and are usually applied when high voltages are to be expected.

The surge protective devices of the first type ascertain that smaller currents flow through the phase conductors while also ascertaining that too high a voltage on the phase conductors is limited to a well defined value. Furthermore, the surge protective device of the second type ascertains that the large lightning current flows via the element into the central conductor which is not provided with a fuse.

In an embodiment of the present invention, the surge protective device of the first type and surge protective device of the second type are included in front of a switch provided in the supply unit, seen in the direction of power flow from the external transformer. This arrangement assures that the currents caused by a lightning strike or EMP do not flow through the switch of the system, resulting in a better protection of one of the elements of the power supply. In former actual cases of damage caused by lightning strike, the switch was completely burnt.

In a further embodiment of the present system, the switch may be switched off by means of an earth leakage circuit breaker. The earth leakage circuit breaker is also protected by the present system. Earth leakage circuit breakers are applied in general for high impedance earth circuit. In a normal arrangement (surge arresters between phase and earth) a defect in one of the surge arresters can lead to two high voltage of the high impedance earth, and thus also for the connected equipment. The normal protection system can thus only be used after the earth leakage circuit breaker, in order to disconnect such an unwanted situation, and as a result, the earth leakage circuit breaker may still be damaged when a lightning strikes. The present invention, however, may be positioned in front of the earth leakage circuit breaker, as by using a spark gap, no galvanic connection as present between the neutral conductor and earth. As a result, the earth (and all connected equipment) cannot be put on too high a voltage when one of the surge arresters fails.

In a further embodiment, the earth leakage circuit breaker is of a self-resetting type. Such an earth leakage circuit breaker will reset after a predetermined period of time, thus reconnecting the power supply automatically. When there still is an earth failure, the eath leakage circuit breaker will switch off again.

In an even further embodiment, the surge protective device of the second type is of the non blowing-off type. The surge protective device of the first type is a voltage dependent resistor or varistor and the surge protective device of the second type is a spark gap element. This arrangement assures that no hot gasses or high pressure occur, which are typical for state of the art spark gap elements which are blowing off.

The elements of the power supply unit are positioned inside a closed cabinet. This allows to build a small and reliable cabinet comprising the elements of the power supply (i.e. power supply connections and the protection circuity), which is moreover cost-effective and easy to assembly. By using surge protective device of the non blowing-off type, the cabinet will not be exposed to high internal pressures or hot gasses. This also has the added advantage that the connection between neutral conductor and surge protective device may be a short connection, which results in less mechanical forces on the connections cansed by strong electromagnetic fields.

The surge protective device of the second type has a rating of at least 40 kA, more preferably at least 5 kA and even more preferably at least 100kA. This will allow an effective surge protection system offering protection to currents which have been encountered in practise after lightning strikes on objects with a small foot print.

The surge protective device of the first type has a rating of at lest 4 kA, more preferably at least 8 kA. This will suffice for the current flowing through these elements occuring after a lightning strike.

The neutral conductors of the system and the interconnections between the neutral conductors have a cross section of at least 8 mm2, more preferably at least 16 mm2. Also the conductors connected to the earth electrodes and all interconnecting items have a cross section of at least 8 mm2, more preferably at least 16 mm2. This should include all connection through which current flows, including interconnection of clamps to which the neutral conductor or earth conductors are connected. The highest currents will flow through the neutral conductors and to the earth electrodes, and as a result the complete path through which these currents flow should have a predetermined minimal diameter. Preferably, at least part of the conductors connected to the earth electrode is formed by a metal plate. This allows are effective flow of the current over the neutral and earth conductors leading to lower electromechanical forces.

Short description of the drawing

The invention will now be explained in further detail referring to the drawing, in which:

  • Fig. 1 shows a schematic diagram of a system for protection of low voltage equipment according to the prior art;
  • Fig. 2 shows a schematic diagram of a first embodiment of a system according to the invention;
  • Fig. 3 shows a schematic diagram of a second embodiment of a system according to the invention.

Detailed description of an embodiment

In Fig 1, which shows the state of the art, I indicates the part which is positionned in the space of the electricity supplies. Three windings of a transformer are referenced by numeral 1, the secondary winding of the transformer being in a star configuration of which the star point is earthed. The impedance existing between the star point and the point of the zero potential is indicated by Ra, which usually has a very low value, e.g. a 0.5 Ohm and a self inductance of e.g. 5 µH. The secondary windings of the transformer usually have a resistance value of about 0.01 Ω and a self inductance of 50 µH. In this space, also the fuses 2 are positioned.

The equipment of the user, in the part indicated with II, comprises a three phase switch 3. Each of the conductors (phase and neutral) is connected behind the switch 3 to a connection 5 via a surge arrester 4, such as a voltage dependent resistor or varistor. The connection 5 is connected to the frame of the switch closet (or object). This connection 5 is being earthed by means of a earth conductor, the impedance of which is Rb. The conductors leading away from the switch 3, which supply the further equipment with energy, are indicated with reference numeral 6 for the phase conductors and reference numeral 7 for the neutral conductor. The further equipment is provided with possible own protection and has a relatively high input impedance.

When a lightning strike hits the frame of the object, the charge must be deflected via the earth conductor 5 to earth. In an ideal case, the impedance Rb, via which the lightning energy is deflected, has a zero value. Standardisation norms for lightning protection require a value of maximum 2.5 Ohm.

A limiting factor for the deflection of the energy caused by the lightning strike is the small ground surface on which the object (or equipment) is usually positioned. The small dimensions of the ground surface prevent a quick deflection of a large amount of charge within a short time period. This substantially enhances the chance of heating of the equipment in the object II and also the risk of voltage flash-over.

In a lightning strike in which a momentary value of the current may be as high as 150 kA, a voltage on the earth conductor 5 may be as high as 75 kV. This voltage may easily flash over to the switch 3, which in normal operation is closed. In almost all situations, such a flash-over will cause severe damage of the switch 3 and often to melting of the fuses 2.

In order to keep the peak voltage as low as possible and to limit the time period as much as possible, surge arresters 4, such as voltage dependent resistors are provided. The largest current will usually flow through the neutral conductor 7, as this has the lowest impedance value.

At a lightning strike on the frame, the resistors 4 will decrease the danger of flash surge to the fuses 2 and switch 3, but the large currents that will flow from part II to part I (of the electricity supplier) will still have values which may be substantially higher than 40 kA, as a result of which still burning phenomena will occur on the fuses 2 and switch 3.

As a result of the arrangement of the object II, this may lead to a prolonged period of time in which the object II is not operational, which disturbs the service supplied by the equipment in an economically non-attractive fashion.

The circuit according to Fig. 2 provides a solution to this problem in accordance with the present invention. The voltage dependent resistors 4, which are on one side connected with the phase conductors 6, are not connected on the other side to the earth conductor 5, but with the neutral conductor 7. The neutral conductor 7 now connects the lightning current arrester 9 with the earth conductor 5.

Such a lightning current arrester, which at flash-over causes a short circuit situation of limited time duration, is known in the art (see e.g. German patent applications DE-A-19 74 2302 and DE-A-19 75 5082 and European patent application EP-A-0 128 344 mentioned in the introduction).

When a lightning strikes the frame of the object II, the peak voltage on the phase conductors 6 will now be largely suppressed by the voltage dependent resistors 4. The lightning current arrester 9 will cause an almost complets short circuit between the neutral conductor 7 and the earth conductor 8, resulting in that the current caused by the strike is only partially deflected from the object II to the tranformer in part I via the phase conductors 6.

The peak current to be deflected, will now be deflected via the parallel circuit of the earth resistance Ra and Rb. Of course, the resistance of the phase conductors 6 and the neutral conductor 7 between the object II and the transformer in part I still plays a role, but in pratical situations this connection will not result in problems because of the low impedance.

Figs 3 shows a further embodiment of the system according to the present invention, in which the switch 3, viewed in the direction of power flow to the equipment in part II, is positioned behind the components for current and voltage suppression. This further reduces the risk of overland of the switch 3 by large currents. The only component in the system upward of the protection system are the fuses 2 of the electricity provider. Although test have shown that the lightning induced currents through the phase conductor 6 are relatively small, it may still occur that the fuses 2 break down. To assure that down time due to blown fuses 2 is minimised, it is preferred that the fuses 2 are of the automatic type, as these can better withstand the lightning induced current than fuses 2 of the melting type. Moreover, the fuses 2 of the automatic type can be reset manually, or form a remote location.

The surge protective device 9 of the second type has a rating of at least 40 kA, more preferably at least 50 KA and even more preferably at least 100 kA. This will allow an effective surge protection system offering protection to currents which have been encountered in practise when lightning strikes on objects with a small foot print. The surge protective devices 4 of the first type have a rating of at least 4 kA, more preferably at least 8 kA. This will suffice for the currents flowing through these elements occurring after a lightning strike.

All elements of the embodiments described above are integrated into a single cabinet. Using a surge protection device 9 of a non blowing-off type will allow to also integrate this element in the cabinet, as no hot gasses or high pressures can occur. To be able to withstand the high currents flowing through it, the neutral conductor 7 and/or earth conductor 5 of the system and the interconnections between them (such as clamps, etc.) are all made of a material having a cross section of at least 8 mm2, and more preferably at least 16 mm2. This should include all connections through which current flows, including interconnections of clamps to which the neutral conductor 7 and/or earth conductor 5 are connected. The highest currents will flow through the neutral conductor 7 and earth conductor 5, and as a result the complete path through which these currents flow should have a predetermined minimal cross section. Preferably, at least part of the earth conductor 5 is formed by a metal plate. This allows an effective flow of the current over the earth conductor 5 leading to lower electromechanical forces. Also, the connections to the earth electrodes (towards Ra and Rb in Figures 2, 3) should have a minimum diameter. In the closed cabinet, special attention should be given to the mounting of the lightning current arrester 9, as the highest current will flow through this element when a lightning strikes. These currents may cause large electromagnetic forces, which may damage the mounting of the element 9.

It is evident that the effect according to the present invention will also occur when the incoming conductors are connected to a kilowatt-hour meter present in the space indicated by roman numeral I.

It will also be clear that the solution according to the present invention is also usable for a single phase power supply.


Anspruch[de]
  1. Spannungaversorgungesystem mit einem Transformator und einem System zum Zwecke des Überspannungsschutzes gegenüber einem Blitzstrom für ein Objekt, wobei das Objekt eine kleine Standfläche aufweist, die nicht grösser als die Dimensionen eines Fusses eines Antennenmastes ist, wobei das System zum Zwecke des überspannugsschutzes eine Versorgungseinheit umfasst, welche Versorgungseinheit mindestens einen Phasenleiter (6) aufweist, der mit einem Neutralleiter (7) über das Mittel einer einzelnen Überspannungsschutzeinrichtung eines ersten Typs (4) für jeden Phasenleiter verbunden ist, und wobei der Neutralleiter (7) mit einer Erdelektrode des Objektes über das Mittel einer einzelnen Überspannungsschutzeinrichtung eines zweiten Typs (9) verbunden ist, wobei die Überspannungsschutzeinrichtung des ersten Typs (4) ein spannungsabhängiger Widerstand oder Varistor mit einem vorbestimmten Nennwert und wobei die Überspannungsschutzeinrichtung des zweiten Typs (9) ein Funkenstreckenelement ist, welches einen vorbestimmten Nennwert aufweist, wobei der besagte erste Nennwert mindestens 4 kA und der besagte zweite Nennwert mindestens 40 kA aufweist, und wobei das System 30 angeordnet ist, dass die Elemente der Versorgungseinheit innerhalb eines einzelnen Gehäuses angeordnet sind und dass der höchste Strom des Blitzstromes durch den Erdleiter (5) und den Neutralleiter (7) fliesst, wobei er über das Funkenstreckenelement innerhalb des einzelnen Gehäuses fliesst, wobei der Neutralleiter (7) und die Erdelektrode als auch die Zwischenverbindungen zwischen ihnen aus einem Material mit einem Querschnitt von mindestens 8 mm 2 bestehen, wobei der Phasenleiter (6) und der Neutralleiter (7), möglicherweise über einen Schalter (3), direkt mit den Leitern verbunden sind, die von dem sekundaren Ausgang des Transformators kommen, wobei die Versorgungseinheit das einzige System zum Überspannungsschutz zwischen dem Transformator und dem zu schützenden Objekt ist.
  2. System nach Anspruch 1, bei dem die Überspannungsschutzeinrichtung des ersten Typs (4) und die Überspannungsschutzeinrichtung des zweiten Typs (9) vor einem Schalter (3) vorgesehen sind, der in der Versorgungseinheit vorgesehen ist, in der Richtung des Leistungsflusses von einem externen Transformator (1) gesehen, dessen sekundärer Ausgang mit der Versorgungseinheit verbunden ist.
  3. System nach einem der vorstehenden Ansprüche, bei dem der Schalter (3) durch einen Fehlerstromschutzschalter ausgeschaltet werden kann.
  4. System nach Anspruch 3, bei dem der Fehlerstromschutzschalter von einem selbst zurücksetzenden Typ ist.
  5. System nach einem der vorstehenden Ansprüche, bei dem die Überspannungsschutzeinrichtung des zweiten Typs (9) nicht durchschlagend ist.
  6. System nach einem der vorstehenden Ansprüche, bei dem die Überspannungsschutzeinrichtung des zweiten Typs (9) einen Nennwert von mindestens 50 kA aufweist, vorteilhafterweise von mindestens 100 kA, und wobei die Überspannungsschutzeinrichtung des ersten Typs (4) einen Nennwert von mindestens 8 kA aufweist.
  7. System nach einem der vorstehenden Ansprüche, bei dem der Neutralleiter (7) des Systems und die Zwischenverbindungen zwischen dem Neutralleiter (7) einen Querschnitt von mindestens 16 mm2 aufweisen.
  8. System nach einem der vorstehenden Ansprüche, bei dem die Leiter, die mit den Erdelektroden (5) des Systems verbunden sind, und die Zwischenverbindungen zwischen den Leitern einen Querschnitt von mindestens 16 mm2 aufweisen.
  9. System nach einem der vorstehenden Ansprüche, bei dem mindestens ein Teil der Leiter, die mit den Erdelektroden (5) verbunden sind, durch eine Metallplatte ausgebildet ist.
Anspruch[en]
  1. Power supply system comprising a transformer and a system for use for surge protection for a lightning current on an object, the object having a small footprint no larger than the dimensions of the foot of an antenna mast, the system for use for surge protection comprising a supply unit which supply unit has at least one phase conductor (6) that is connected to a neutral conductor (7) by means of a single surge protective device of a first type (4) for each phase conductor, and wherein the neutral conductor (7) is connected to a an earth electrode of the object by means of a single surge protective device of a second type (9), the surge protective device of the first type (4) being a voltage dependent resistor or varistor with a predetermined first rating and the surge protective device of the second type (9) being a spark gap element which has a predetermined second rating and said first rating is at least 4 kA and the second rating is at least 40 kA, and the system is arranged such that the elements of the supply unit are positioned inside a single cabinet and such that the highest current of the lightning current is flowing through the earth conductor (5) and the neutral conductor (7) whereby flowing through said spark gap element within said single cabinet, the neutral conductor (7) and the earth electrode as well as interconnections between them being made of a material with a cross section of at least 8 mm2, the phase conductor (6) and the neutral conductor (7), possibly via a switch (3), directly being connected to the conductors coming from the secondary output of the transformer, whereby the supply unit is the only system for surge protection between the transformer and the object to be protected.
  2. System according to claim 1, in which the surge protective device of the first type (4) and surge protective device of the second type (9) are included in front of a switch (3) provided in the supply unit, seen in the direction of power flow from an external transformer (1) of which the secondary output is connected to the supply unit.
  3. System according to one of the preceding claims, in which the switch (3) may be switched off by means of an earth leakage circuit breaker.
  4. System according to claim 3, in which the earth leakage circuit breaker is of a self-resetting type.
  5. System according to one of the preceding claims, in which the surge protective device of the second type (9) is non blowing-off.
  6. System according to any of the preceding claims, in which the surge protective device of the second type (9) has a rating of at least 50 kA, and even more preferably of at least 100 kA and wherein the surge protective device of the first type (4) has a rating of at least 8 kA.
  7. System according to any of the preceding claims, in which the neutral conductor (7) of the system and the interconnections between the neutral conductor (7) have a cross section of at least 16 mm2.
  8. System according to any of the preceding claims, in which the conductors connected to the earth electrodes (5) of the system and the interconnections between the conductors have a cross section of at least 16 mm2.
  9. System according to any one of the preceding claims, in which at least part of conductors connected to the earth electrode (5) is formed by a metal plate.
Anspruch[fr]
  1. Système d'alimentation électrique comprenant un transformateur et un système à utiliser pour la protection contre les surtensions en cas de courant de foudre frappant un objet, la surface de sol occupée par l'objet étant réduite et non supérieure aux dimensions du pied du mât d'antenne, le système à utiliser pour la protection contre les surtensions comprenant une unité d'alimentation, laquelle unité d'alimentation comprend au moins un conducteur de phase (6) connecté à un conducteur neutre (7) au moyen d'un seul dispositif de protection contre les surtensions d'un premier type (4) pour chaque conducteur de phase, et dans lequel le conducteur neutre (7) est connecté à une électrode de mise à la terre de l'objet au moyen d'un seul dispositif de protection contre les surtensions d'un second type (9), le dispositif de protection contre les surtensions du premier type (4) étant une résistance ou une varistance dépendant de la tension présentant une première valeur nominale prédéterminée, et le dispositif de protection contre les surtensions du second type (9) étant un élément éclateur présentant une seconde valeur nominale prédéterminée, ladite première valeur nominale étant égale à au moins 4 kA, et la seconde valeur nominale étant égale à au moins 40 kA, et le système est agencé de telle sorte que les éléments de l'unité d'alimentation soient positionnés à l'intérieur d'un seul coffret et que le courant le plus élevé du courant de foudre s'écoule à travers le conducteur de mise à la terre (5) et le conducteur neutre (7), s'écoulant ainsi à travers ledit élément éclateur à l'intérieur dudit seul coffret, le conducteur neutre (7) et l'électrode de mise à la terre, ainsi que les interconnexions entre ceux-ci, étant constitués d'une matière dont la section transversale est égale à au moins 8 mm2, le conducteur de phase (6) et le conducteur neutre (7), éventuellement par l'intermédiaire d'un commutateur (3), étant directement connectés aux conducteurs provenant de la sortie du secondaire du transformateur, l'unité d'alimentation étant de ce fait le seul système pour la protection contre les surtensions entre le transformateur et l'objet à protéger.
  2. Système selon la revendication 1, dans lequel le dispositif de protection contre les surtensions du premier type (4) et le dispositif de protection contre les surtensions du second type (9) sont placés devant un commutateur (3) prévu dans l'unité d'alimentation, quand on regarde dans la direction d'un écoulement de courant à partir d'un transformateur externe (1) dont la sortie du secondaire est connectée à l'unité d'alimentation.
  3. Système selon l'une quelconque des revendications précédentes, dans lequel le commutateur (3) peut être mis en position de coupure au moyen d'un disjoncteur de fuite à la terre.
  4. Système selon la revendication 3, dans lequel le disjoncteur de fuite à la terre est du type à réarmement automatique.
  5. Système selon l'une quelconque des revendications précédentes, dans lequel le dispositif de protection contre les surtensions du second type (9) est du type sans soufflage.
  6. Système selon l'une quelconque des revendications précédentes, dans lequel le dispositif de protection contre les surtensions du second type (9) présente une valeur nominale égale à au moins 50 kA, et encore plus préférablement, égale à au moins 100 kA, et dans lequel le dispositif de protection contre les surtensions du premier type (4) présente une valeur nominale égale à au moins 8 kA.
  7. Système selon l'une quelconque des revendications précédentes, dans lequel le conducteur neutre (7) du système, ainsi que les interconnexions avec le conducteur neutre (7), présentent une section transversale égale à au moins 16 mm2.
  8. Système selon l'une quelconque des revendications précédentes, dans lequel les conducteurs connectés aux électrodes de mise à la terre (5) du système, ainsi que les interconnexions entre les conducteurs, présentent une section transversale égale à au moins 16 mm2.
  9. Système selon l'une quelconque des revendications précédentes, dans lequel au moins une partie des conducteurs connectés à l'électrode de mise à la terre (5) est formée par une plaque de métal.






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