Patent Description:
A surge arrester is a device for protecting an electrical equipment from over-voltages caused by, e.g., lightning or switching operations.

To protect a unit of equipment from transients occurring on an attached conductor, a surge arrester is connected to the conductor, typically just before it enters an interior of the equipment. The surge arrester is also connected to ground and functions by routing energy from an over-voltage transient to ground if one occurs, while isolating the conductor from ground at normal operating voltages. This is usually achieved through use of a varistor, which has substantially different resistances at different voltages. Typically, the varistor is arranged within a housing of the surge arrester.

Under a fault condition, such as a short circuit event, the varistor heats and an arc occurs in the surge arrester causing an increase in pressure within the housing of the arrester. Usually, the varistor breaks under such circumstances. Generally, there is a risk that the arc burns through the housing, leading to a violent shattering and ejection of critical parts.

<CIT> discloses a surge arrester including an outer porcelain housing and an ablative heat shield liner along with techniques for making the surge arrester break resistant. A blow out or relief valve is provided on at least one end of the arrester housing for venting internal pressure due to electrical arcing therein.

<CIT> relates to a surge arrester comprising an active part, an electrically insulating part of a casing, a partition which protects the interior surface of the insulator, a closing cover, a lower frame which is closed by a zone of lower mechanical resistance in the form of a safety membrane and a metal base which supports the active part.

<CIT> relates to an arrester with an insulation sleeve having a conductor at its fore-end part, an arrester elements stack inserted in an inside of the insulation sleeve through a high-voltage electrode, an earthed electrode arranged at the rear-end part side of the arrester elements stack, a coil-shaped spring arranged at the rear-end part side of the earthed electrode concentrically to the insulation sleeve, a metal case surrounding the insulation sleeve, the earthed electrode and the spring, and a sealing member installed at the opening port of the rear-end part side of the metal case. The outer diameter of the rear-end part side of the insulation sleeve is smaller than the outer diameter of the center part of the insulation sleeve. Also, a tapered outer surface is provided at the outer circumference of the fore-end part of the insulation sleeve.

<CIT> relates to a circuit interrupter in combination with a lightning arrester comprising a housing, a cap, a filling, and a depending stem of reduced diameter having an internal chamber. A peripheral groove is configured to weaken the stem so that the portion of the stem below the groove and parts carried thereby will be broken away from the portion of the stem above the groove when the circuit interrupter operates. Enclosed within the chamber is a spark gap defined conjointly by a downwardly projecting upper electrode and a lower electrode. The lower electrode has a threaded shank which passes through an aperture in a lower portion of the stem.

<CIT> relates to a surge arrester with a housing and a bottom cover assembly. Within the housing are resistance blocks and electrode sections. A gasket is positioned between the housing and a ground lead terminal housing. In electrical contact with electrode section is a solid non-deflectable metal plate resting upon an annular step of the terminal housing. Further, a spring washer is seated in the housing. A ground lead terminal is supported by the housing. A projection extends from the terminal and holds an explosive cartridge. In the event that lightning current damages the electrode structure, continued flow of current before interruption will cause gun powder in cartridge to explode. The explosion causes the ground terminal housing to break at its weakest point, an annular section between those surfaces of the housing which support the spring washer and the ground lead terminal.

There is a need for a further improved or alternative surge arrester.

This object is achieved by the independent claim <NUM>. Dependent claims refer to preferred embodiments. Additional or alternative aspects of the present disclosure are addressed throughout this specification.

According to the present disclosure, a surge arrester is provided that comprises an elongate housing, an active member, and an enclosure. The elongate housing has an interior comprising an interior surface that extends along a longitudinal axis between a first end and a second end of said housing. The active member is arranged at least partially within the interior and extending along the longitudinal axis. The enclosure is fixed to or integrally formed with the housing and closes the interior at the first end. The enclosure comprises a predetermined breaking line.

In the event of a fault condition, e.g., a short circuit condition, the pressure within the housing increases and the predetermined breaking line allows for a defined breaking of the enclosure. This may allow part of the enclosure to break off while the remaining part of the enclosure may stay connected to or formed with the housing.

The active member may have a cross-section that extends, at least partly, radially beyond the breaking line. The cross-section of the active member is particularly a cross-section normal, i.e. perpendicular, to the longitudinal axis. Radially may be understood herein so as to refer to a direction generally perpendicular to the longitudinal axis. Thus, the active member may move, caused by the increased pressure, along the longitudinal axis towards the first end. However, this movement can be stopped since the active member has a cross-section that extends, at least partly, radially beyond the breaking line. Thus, while controlled movement of the active member is admitted to at least some extent, an uncontrolled ejection of critical parts can be reliably prevented. In this manner the operational safety of the surge arrester is increased.

The breaking line extends around the longitudinal axis, defining an inner enclosure portion and an outer enclosure portion. The inner enclosure portion is particularly a radially inner portion of the enclosure with respect to the longitudinal axis or an axis parallel thereto. Preferably, the longitudinal axis intersects the inner enclosure portion. The outer enclosure portion is particularly a radially outer portion of the enclosure with respect to the longitudinal axis. The inner enclosure portion and the outer enclosure portion may solely be separated from each other by the predetermined breaking line.

The design of the surge arrester is such that a pressure increase due to a short circuit event effectuates a breaking of the enclosure along the predetermined breaking line, such that the inner enclosure portion separates from the outer enclosure portion, wherein the outer enclosure portion remains connected to the housing, and wherein an opening in the outer enclosure portion is formed at the place where the inner enclosure portion has been located prior to the breaking.

The surge arrester is particularly suitable if it is a medium voltage surge arrester. Herein "medium voltage" is understood as indicating a voltage range between <NUM> kV to <NUM> kV.

The surge arrester may be designed such that an axial movement of the active member along the longitudinal axis towards the first end, for example caused by a short circuit event, interferes with the outer enclosure portion of the enclosure. More specifically, the outer enclosure portion may be designed to stop the axial movement of the active member along the longitudinal axis towards the first end. Thus, a defined movement may be promoted while said movement can be stopped particularly reliable.

The housing and the enclosure may be formed integral, i.e., as a one-piece element. Alternatively, the enclosure and the housing may be formed by separate parts. Preferably, the enclosure is fixed to the housing in a fluid-tight or gas-tight manner.

The inner surface of the housing may be coated by a coating layer comprising or consisting of an arc-quenching material, e.g., melamine, aromatic epoxy resin, linear aliphatic epoxy resin, aluminum hydroxide, or metal hydride.

The enclosure may extend at least substantially perpendicular to the longitudinal axis.

The breaking line and thus the radially inner end of the outer enclosure portion may be substantially ring-shaped. Thus, a stopping function of the outer enclosure portion can be achieved that is particularly uniform or symmetrical with respect to the longitudinal axis. However, other shapes may be chosen.

The surge arrester may further comprise a first discharge electrode provided at the first end of the housing, and a second connection electrode for connection to an electrical equipment, wherein the second connection electrode is provided at the second end of the housing. The active member may extend along the longitudinal axis between the first discharge electrode and the second connection electrode.

The active member may further comprise an insulation member, arranged at least partially within the interior of the housing. The insulation member may particularly comprise or be made from an electrically isolating material.

The active member may comprise a first active member portion having a first cross-sectional extent, and a second active member portion having a second cross-sectional extent, the second cross-sectional extent extending radially beyond the first cross-sectional extent. A cross-sectional extent of the predetermined breaking line may be radially completely contained within the second cross-sectional extent. In this manner, the second active member portion can stop the movement of the active member along the longitudinal axis, while the first active member portion may at least partly move through the opening formed within the outer enclosure portion allowing a particularly suited and defined pressure release.

A shoulder may be provided at a transition from the first to the second active member portion. The first active member portion may be provided closer to the first end than the second active member portion. For example, the shoulder may be a rib, preferably a circumferentially extending rib. Alternatively, the shoulder may be a radially extending protrusion, for example one or several radially extending protrusions.

The shoulder may be formed by the insulation member.

The second active member portion may be designed to break in case of a short circuit event.

The relative cross-sections of the first active member portion and the inner enclosure portion may be such that the first mentioned cross-section may extend through the latter-mentioned, and that the cross section of the second active member portion is at least partly larger than that of the inner enclosure portion such that it may not extend through the opening resulting from the inner enclosure's breaking along the breaking line.

The second active member portion may comprise an outer wall portion that is shaped cylindrically with respect to the longitudinal axis in such a way that a movement of the outer wall portion along the longitudinal axis is guided by the interior surface. Alternatively, different mating shapes allowing such guidance may be foreseen. The interior surface of the interior of the housing may be shaped at least partly cylindrical. Particularly, the interior surface and the outer wall portion of the second active member portion may be shaped complementary to each other in such a way, that the second active member portion is guided by the interior surface during the movement of the active member along the longitudinal axis towards the first end.

The predetermined breaking line may at least substantially be circular. This is advantageous, since it may allow for a particularly easy manufacture and good distribution of forces.

The enclosure may support the active member, preferably by supporting the first discharge electrode.

The surge arrester may further comprise a biased member that is arranged with respect to the longitudinal axis between the active member and the inner enclosure portion and that is biased in a direction parallel to the longitudinal axis. This may allow for a reliably positioning of the active member. Moreover, the biased member may support a breaking of the enclosure along the breaking line in a short circuit event, particularly by transmitting respective forces to the inner enclosure portion. Preferably, the biased member is arranged such that it causes a pressure acting against the active member directed along the longitudinal axis towards the second end of the housing.

The biased member may, at least to a first approximation, be ring-shaped and arranged surrounding the longitudinal axis. This may allow for a particularly uniform distribution of pressure with respect to the longitudinal axis.

The discharge electrode may be electrically and mechanically connected to the active member and extend through a through hole formed in the inner enclosure portion to the outside of the housing.

The biased member may surround the discharge electrode.

The subject-matter of the disclosure will be explained in more detail with reference to preferred exemplary embodiments which are illustrated in the attached drawings, in which:.

<FIG> a is a schematic cross-sectional view of a surge arrester according to the present disclosure. The surge arrester comprises an elongate housing <NUM>, a first discharge electrode <NUM>, a second connection electrode <NUM>, an active member <NUM>.

The elongate housing <NUM> has an interior <NUM> comprising an interior surface <NUM> that extends along a longitudinal axis L between a first end <NUM> and a second end <NUM> of the housing <NUM>.

The surge arrester according to this example is formed as a plug-in surge arrester, where the longitudinal axis L is parallel to a corresponding plug-in direction. The housing <NUM> comprises a fastening means <NUM> for fastening the housing <NUM> to an electrical equipment, e.g., a high-voltage installation.

The first discharge electrode <NUM> is provided at the first end <NUM> of the housing <NUM>. The first discharge electrode <NUM> may constitute a grounding terminal. The second connection electrode <NUM> is for connection to the electrical equipment. The second connection electrode <NUM> is provided at the second end <NUM> of the housing <NUM>. The second electrode <NUM> may constitute a plug-in contact.

The active member <NUM> is arranged at least partially within the interior <NUM> and extending along the longitudinal axis L between the first and second electrodes <NUM>, <NUM>. The active member <NUM> may comprise a non-linear, voltage-dependent resistance element, for example including at least one varistor.

The active member <NUM> further comprises an insulation member <NUM>, arranged at least partially within the interior <NUM>. The insulation member <NUM> surrounds the resistance element of the active member <NUM> as seen within a normal cross-section normal, i.e., a cross-section perpendicular to the longitudinal axis L. The insulation member <NUM> may comprise an insulating cone portion <NUM> protruding along the longitudinal axis L beyond the second end <NUM> of the housing <NUM>.

When the surge arrester is fitted into the electrical equipment, the active member <NUM> may be plugged into a socket <NUM> of the electrical equipment and the housing <NUM> can be fixed to the electrical equipment, for example via the socket <NUM>, by the fastening means <NUM>, for example via a screw <NUM>. During plugging, the connection electrode <NUM> of the surge arrester is electrically connected to a current conductor of the electrical equipment. Concurrently, the insulating cone portion <NUM> and a mating insulating cone-shaped opening <NUM> of the socket <NUM> are pressed against each other. This achieves a suited plug-in connection which can withstand high loads and has a dielectrically high-grade insulation.

The surge arrester further comprises an enclosure <NUM>. The enclosure <NUM> is fixed to or integrally formed with the housing <NUM> and closes the interior <NUM> at the first end <NUM>. In <FIG>, said enclosure <NUM> is shown as being integrally formed with the housing <NUM>. It may, however, also be a part sperate and affixed thereto. The enclosure <NUM> comprises a predetermined breaking line <NUM> extending, for example annular or circular, around the longitudinal axis L, defining a radially inner enclosure portion <NUM> and a radially outer enclosure portion <NUM>. By a breaking of the breaking line <NUM>, the inner enclosure portion <NUM> can be completely separated from the outer enclosure portion <NUM>.

The active member <NUM> has a normal cross-section, i.e., a cross-section perpendicular to the longitudinal axis L, that extends, at least partly, radially, i.e., radially outwardly from the longitudinal axis L beyond the breaking line <NUM>. The normal cross-section of the active member <NUM> may vary in dependence on the position with respect to the longitudinal axis L. Thus, the active member <NUM> has at least at one position along the longitudinal axis L a normal cross-section that extends at least partly, radially beyond the breaking line <NUM>. Preferably, the active member <NUM> has at least at one position along the longitudinal axis L a normal cross-section that extends completely, i.e., in a circumferential manner or ring-shaped manner, radially beyond the breaking line <NUM>. Practically speaking, a portion of the active member <NUM> that extends radially beyond the breaking line <NUM> will interfere, upon axial movement of the active member in the direction of the second end <NUM>, with the outer portion <NUM> of the enclosure <NUM>. Axial movement is therefore limited.

If a pressure within the housing <NUM> increases, for example due to a fault condition, such as a short circuit event, the active member <NUM> may break, typically near the second end <NUM> of the housing <NUM>, as illustrated in <FIG> and a portion of the active member <NUM> may be caused - by the increased pressure - to move along the longitudinal axis L toward the first end <NUM>. Since the active member <NUM> has a normal cross-section that extends, at least partly, radially beyond the breaking line <NUM>, this movement is stopped reliably by an interference between the active member <NUM> and the outer enclosure portion. In this manner, a well-defined pressure relief can be achieved, and an uncontrolled ejecting of critical parts can be prevented.

Accordingly, the surge arrester is preferably designed such that an axial movement of the active member <NUM> along the longitudinal axis L towards the first end <NUM> that is caused by a fault condition, such as a short circuit event, interferes with the outer enclosure portion <NUM> of the enclosure <NUM>. More specifically, the outer enclosure portion <NUM> is designed to stop the axial movement of the active member <NUM> along the longitudinal axis L towards the first end <NUM>. To this end, the outer enclosure portion <NUM> may be connected to the remainder of the housing <NUM> in an integral or one-piece manner. Alternatively, the enclosure may be formed by a separate part that is fixed to the housing <NUM> in a fluid-tight manner.

As exemplarily illustrated in <FIG> and <FIG>, the active member <NUM> may comprise a first active member portion <NUM> having a first cross-sectional extent, and a second active member portion <NUM> having a second cross-sectional extent, where the second cross-sectional extent extends radially beyond the first cross-sectional extent. For example, the first cross-sectional extent and the second cross-sectional extent may be circular, respectively. More specifically, the first active member portion <NUM> may have an outer surface that is shaped cylindrical with respect to the longitudinal axis L, having a first diameter D1, and the second active member portion <NUM> may have an outer surface that is shaped cylindrical with respect to the longitudinal L, having a second diameter D2, wherein second diameter D2 is larger than the first diameter.

The predetermined breaking line <NUM> may be circular, having a diameter d, where the diameter d of the breaking line <NUM> is larger than the first diameter D1 and smaller than the second diameter D2, i.e., D1 < d < D2. In this way, the axial movement of the active member <NUM> along the longitudinal axis L can be reliably stopped by an interaction between the second active member portion <NUM> and the outer enclosure portion <NUM>.

At a transition from the first active member portion <NUM> to the second active member portion <NUM>, a shoulder <NUM> is formed, for example having a conical surface.

More generally, the cross-section of the active member <NUM>, the first active member <NUM>, and the second active member <NUM> is not necessarily circular. However, preferably, a cross-section, i.e. a circumferential extension of the first active member portion <NUM> extends through the cross-section of the inner enclosure portion <NUM>, and a cross section of the second active member portion <NUM> is at least partly, preferably circumferentially completely larger than the cross-section of the inner enclosure portion <NUM> such that it may not extend therethrough.

In the illustrated example, the second active member portion <NUM> comprises an outer wall portion <NUM> that is shaped cylindrically with respect to the longitudinal axis L in such a way that a movement of the outer wall portion <NUM> along the longitudinal axis L is guided by the interior surface <NUM>. To this end, the interior surface <NUM> is preferably shaped cylindrically complementary to the outer wall portion <NUM> of the second active member portion <NUM> in such a way, that the second active member portion <NUM> is guided by the interior surface <NUM> during the movement of the active member <NUM> along the longitudinal axis L towards the first end <NUM> of the housing <NUM>.

The inner enclosure portion <NUM> supports the active member <NUM>, directly or indirectly. For example, the enclosure <NUM> may support the active member <NUM> by supporting the first discharge electrode <NUM>.

As illustrated for example in <FIG>, the surge arrester may further comprise a biased member <NUM>, where the inner enclosure portion <NUM> supports the active part <NUM> (e.g., via the discharge electrode <NUM>) by way of the biased member <NUM>, directly or indirectly via further parts. The biased member <NUM> may be for example a spring. The biased member <NUM> is preferably arranged with respect to the longitudinal axis L between the active member <NUM> and the inner enclosure portion <NUM> and being biased in a direction parallel to the longitudinal axis L. The biased member <NUM> preferably is arranged such that it causes a pressure acting against the active member <NUM> directed along the longitudinal axis L towards the second end <NUM> of the housing <NUM>. If the biasing member <NUM> is a spring, it is preferably strongly compressed in the biasing state, such that it on the one hand exerts a suitable biasing force and on the other hand may directly transfer forces from the active member to the inner enclosure portion, resulting in breaking along the breaking line <NUM> in case of a fault.

For example, the biased member <NUM> is ring-shaped and arranged surrounding the longitudinal axis L. This allows for a particularly uniform flux of force between the inner enclosure portion <NUM> and the active member <NUM>.

In the illustrated example, the discharge electrode <NUM> is electrically and mechanically connected to the active member <NUM>. The inner enclosure portion <NUM> shows a central through hole <NUM>, where the discharge electrode <NUM> extends through the through hole <NUM>. Thus, the discharge electrode <NUM> can be connected electrically easily from outside the housing <NUM> of the surge arrester. The biased member <NUM> surrounds the discharge electrode <NUM> as seen in a normal cross-section.

The surge arrester may further comprise a centering element <NUM> for centering the first discharge electrode <NUM>, arranged, at least partly between the inner enclosure portion <NUM> and the active member <NUM> or a portion of the discharge electrode <NUM>. The inner enclosure portion <NUM> may support the active member <NUM> via the centering element <NUM>. For example, the inner enclosure portion <NUM> may support the discharge electrode <NUM> via both, the centering element <NUM> and the biased element <NUM>.

Further, the centering element <NUM> preferably comprises a tube-shaped portion <NUM> for centering the discharge electrode <NUM> with respect to the longitudinal axis L. In the illustrated example, the tube-shaped portion <NUM> to this end extends through the through-hole <NUM> of the inner enclosure portion <NUM>.

As illustrated in <FIG>, the surge arrester may further comprise a breaking supporting member <NUM> that is designed to support a breaking of the enclosure <NUM> at the predetermined breaking line <NUM> in case of a short-circuit event or similar fault condition. Preferably, the breaking support member <NUM> is fixed to the active member and/or the discharge electrode <NUM>, directly or indirectly.

The breaking supporting member <NUM> may comprise a sharp edge portion <NUM> that is preferably shaped complementary to the breaking line <NUM>. The edge portion <NUM> preferably is arranged, as seen along the longitudinal axis L, at a small distance ε from the breaking line <NUM>. For example, the small distance ε may be less than <NUM>% of the first diameter D1 of the first active member portion <NUM>.

Claim 1:
A surge arrester, comprising
an elongate housing (<NUM>) having an interior (<NUM>) comprising an interior surface (<NUM>) that extends along a longitudinal axis (L) between a first end (<NUM>) and a second end (<NUM>) of said housing (<NUM>);
an active member (<NUM>), arranged at least partially within the interior (<NUM>) and extending along the longitudinal axis (L);
an enclosure (<NUM>) that is fixed to or integrally formed with the housing (<NUM>) and that closes the interior (<NUM>) at the first end (<NUM>),
wherein the enclosure (<NUM>) comprises a predetermined breaking line (<NUM>),
wherein the breaking line (<NUM>) extends around the longitudinal axis (L), defining a radially inner enclosure portion (<NUM>) and a radially outer enclosure portion (<NUM>), wherein the radially inner enclosure portion (<NUM>) is configured to support the active member (<NUM>).