WO2019064014A1

WO2019064014A1 - Electrically heated conduit

Info

Publication number: WO2019064014A1
Application number: PCT/GB2018/052769
Authority: WO
Inventors: Neil Malone; Jason Daniel Harold O'connor; Peter Richard HOWE; Ian James SCOTT
Original assignee: Heat Trace Limited
Priority date: 2017-09-29
Filing date: 2018-09-28
Publication date: 2019-04-04
Also published as: GB2566984B; GB201715850D0; GB2566984A

Abstract

An electrically heated conduit (100) comprises a conduit (300) for conveying fluid, the conduit having a length L, and an electrical heater (800). The electrical heater (800) comprises first, second, and third conductors (1, 2, 3) wherein each of the first, second, and third conductors extends along the length of the conduit (300), a fourth conductor (4) disposed around the conduit (300) and extending along the length of the conduit (300), and an electrical heating element (5) disposed between the fourth conductor (4) and the first, second and third conductors (1, 2, 3). The electrical heating element (5) is arranged to generate heat when an electrical current is passed between the fourth conductor (4) and one or more of the first, second and third conductors (1, 2, 3).

Description

Electrically Heated Conduit

The present invention relates to an electrically heated conduit. More particularly, but not exclusively, the present invention relates to an electrically heated conduit having a three- phase electrical heater, which is suitable for use in large scale applications.

Pipelines are commonly used for the transportation of fluid (for example, water, gas, or petroleum products). Depending upon the environment where the pipelines are located, it is often required to provide an electrical heater to heat the pipelines, so as to ensure that the contents of the pipelines are maintained at a certain temperature, for example above the freezing point of the contents. For large scale industrial applications, such as cross-country pipeline transport, it is common for pipelines to have a length of hundreds or even thousands of kilometres. Given the substantial length of pipelines to be heated in those applications, it is desirable for the electrical heater to have a long circuit length, so as to reduce the complexities and difficulties of supplying power to the electrical heater. It is also desirable to improve the efficiency of the electrical heater so as to reduce the overall costs of providing electrical heating to lengthy pipelines.

It is an object of the present invention, among others, to provide an electrically heated conduit, which is suitable for use in large scale applications.

According to a first aspect of the invention, there is provided an electrically heated conduit, which comprises: a conduit for conveying fluid, the conduit having a length; and an electrical heater. The electrical heater comprises: first, second, and third conductors, wherein each of the first, second, and third conductors extends along the length of the conduit; a fourth conductor disposed around the conduit and extending along the length of the conduit; and an electrical heating element disposed between the fourth conductor and the first, second and third conductors, the electrical heating element being arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors.

By arranging an electrical heating element to be disposed between the fourth conductor and the first, second and third conductors and to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors, the first, second and third conductors are allowed to be electrically coupled to a common node, i.e., the fourth conductor, via the electrical heating element. In this way, the electrical heater is electrically connected in a wye configuration (i.e., star configuration) with the fourth conductor being the wye point (i.e., star point). Each of the first, second, and third conductors is therefore electrically connected to the wye point via at least a part of the electrical heating element, thereby forming three phases of the electrical heater. Accordingly, the first, second, and third conductors may be suitable for connecting to a three- phase electric power supply, thereby allowing the electrical heater to function as a three- phase electrical heater to heat up the conduit. Generally speaking, a three-phase electrical heater is typically able to achieve a circuit length of several kilometres to tens of kilometres, which satisfy the length requirements to electrical heaters in large-scale applications. The electrical heater is therefore suitable for use with three-phase electric power supplies which are widely available in industrial applications and is capable of achieving a relatively long circuit length of the order of tens of kilometres.

The fourth conductor may be configured to, in use, distribute heat generated by the electrical heating element around the conduit. The provision of the fourth conductor is beneficial in that it allows the electrical heater to heat up the contents of the conduit substantially evenly around an outer surface of the conduit. By distributing heat around the conduit, the electrical heater is more efficient in maintaining a temperature of the contents of the conduit, in contrast to a scenario where the generated heat is confined within discrete portion(s) of the conduit. Therefore, the fourth conductor allows the contents of the conduit to be heated evenly and also improves the energy efficiency of the electrical heater.

In the expression "a fourth conductor disposed around the conduit", the term "disposed around" is not intended to mean that the fourth conductor is required to be in direct contact with an outer surface of the conduit. Indeed one or more additional layers (such as the first, second and third conductors and the electrical heating element of the electrical heater) may be disposed between the conduit and the fourth conductor. It will be appreciated that, alternatively, the fourth conductor and the electrical heating element may be disposed between the conduit and the first, second and third conductors.

The electrical heating element may be electrically resistive.

The electrical heating element may be an electrically resistive polymeric material. The electrical heating element may comprise an electrically-conductive material distributed within an electrically-insulating polymer. The electrically-conductive material may be selected from carbon black, graphite, graphene, carbon fibres, carbon nanotubes, metal powders, metal strand and metal coated fibres. The electrically insulating polymer may typically be selected from polypropylene and polyethylene.

The first, second and third conductors may be configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the first, second and third conductors are separated from each other of the first, second and third conductors around a perimeter of the conduit.

A separation between adjacent ones of the first, second and third conductors may remain substantially constant along the length of the conduit. This allows the electrical performance of the electrical heater to be substantially uniform along the length of the conduit.

The electrical heating element may have a thickness along a radial direction of the conduit, and a separation between adjacent ones of the first, second and third conductors may be greater than the thickness of the electrical heating element. It will be appreciated that the "thickness" of the electrical heating element may refer to a thickness of the electrical heating element that is disposed between the fourth conductor and one of the first, second and third conductors. The electrical heating element may comprise a first section which is disposed between the fourth conductor and one of the first, second and third conductors, and a second section which is not disposed between the fourth conductor and one of the first, second and third conductors. The first section of the electrical heating element may be regarded as an active heat generation region, which excludes the second section. Accordingly, the "thickness" of the electrical heating element may refer to a thickness of the active heat generation region of the electrical heating element. By arranging the separation to be greater than the thickness of the electrical heating element, a majority of a current flowing out of each of the first, second and third conductors tends to follow an electrical pathway from a respective one of the first, second and third conductors, via the electrical heating element and the fourth conductor, and to another one of the first, second and third conductors. This reduces the current density along an alternative electrical pathway between adjacent ones of the first, second and third conductors, which allows a path on a surface of the electrical heating element around the perimeter of the conduit without passing via the fourth conductor. If the separation is small, the alternative electrical pathway may experience high current density and may cause thermal stress and early failure of the electrical heating element. Thus, by increasing the separation, it is possible to reduce the current density along the alternative electrical pathway, thereby prolong the lifespan of the electrical heating element, and enhance the heat distribution efficiency around the conduit. The separation between adjacent ones of the first, second and third conductors may be at least three times the thickness of the electrical heating element. In this way, the current flowing along the alternative electrical pathway which does not pass via the fourth conductor is negligible compared to the current flowing through the fourth conductor. Therefore, the lifespan of the electrical heating element and the heat distribution efficiency around the conduit are further improved.

The first, second and third conductors may be evenly spaced apart from each other around the perimeter of the conduit. The first, second and third conductors may be configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the first, second and third conductors has a respective dimension around a perimeter of the conduit.

The first, second and third conductors may have equal dimensions around the perimeter of the conduit.

By arranging the first, second and third conductors to have equal dimensions around the perimeter of the conduit, it allows each of the first, second and third conductors to be electrically coupled to the fourth conductor via equal dimensions of the electrical heating element, and further allows the electrical heating element to contribute equal electrical resistances (per unit length of the conduit) between the fourth conductor and each of the first, second and third conductors. Accordingly, the electrical heater, when connected to a three- phase electric power supply, has electrically conductive pathways of equal resistances across the three phases and will draw equal currents from each phase of the three-phase power supply. Therefore, the three phases of the electrical heater are balanced.

A respective dimension of one of the first, second and third conductors around the perimeter of the conduit may be at least around three times a separation between adjacent ones of the first, second and third conductors around the perimeter of the conduit.

That is, the first, second and third conductors together cover a significant portion (e.g., at least 75%) of the perimeter of the conduit.

By arranging a respective dimension of one of the first, second and third conductors around the perimeter of the conduit to be at least around three times a separation between adjacent ones of the conductors, each of the conductors is allowed to have a significant dimension around the perimeter of the conduit, such that the thickness of the conductors along the radial direction of the conduit can be reduced to be very thin along the radial direction R of the conduit, while a cross-sectional area of each conductor is maintained at a desired level. The cross-sectional area of each conductor affects the resistance of each conductor, which further affects the amount of voltage drop per unit length of each conductor and accordingly the maximum circuit length achievable by the electrical heater. Therefore, maintaining the cross-sectional area of each conductor at a desired level is important for the electrical heater to achieve a target circuit length.

The thickness of the first, second and third conductors may be less than a dimension of each of the first, second and third conductors around a perimeter of the conduit. Preferably, the thickness may be less than one tenth of the dimension. In this way, the first, second and third conductors form a thin "coat" covering the conduit and do not substantially increase a cross-sectional size of the electrically heated conduit. This facilitates the manufacturing and installation of the electrically heated conduit. Further, by arranging a respective dimension of one of the first, second and third conductors around the perimeter of the conduit to be at least around three times a separation between adjacent ones of the conductors, a majority of a perimeter of the conduit can be directly heated up by electrical current flowing through the electrical heating element. This allows heat generated by the electrical heater to be efficiently transferred to the contents of the conduit and also facilitates heat distribution around the conduit.

Each of the first, second, and third conductors may be electrically coupled to the fourth conductor via the electrical heating element.

The electrical heating element may be disposed around the fourth conductor, and the first, second, and third conductors may be further disposed around the electrical heating element. Alternatively, the electrical heating element may be disposed around the first, second, and third conductors, and the fourth conductor may be further disposed around the electrical heating element.

Each of the first, second, and third conductors may extend along a direction parallel to a central axis of the conduit. Each of the first, second, and third conductors may be aligned with the central axis of the conduit and may have a length which is substantially equal to a length of the conduit. This arrangement of the conductors is advantageous in that, for a predetermined length of conduit, each of the first, second, and third conductors is of a minimum overall length (i.e., a length substantially equal to the length of the conduit), and accordingly, the resistance of each conductor and the amount of voltage drop on each conductor per unit length of the conduit is minimised, thereby allowing the electrical heater to achieve a maximum circuit length.

The electrical heating element may comprise a plurality of heating element sections which are spaced apart from each other. The plurality of heating element sections may not be directly connected to each other. Each of the plurality of heating element sections may be disposed between the fourth conductor and a respective one of the first, second and third conductors. The plurality of heating element sections may form the active heat generation region of the electrical heating element.

The plurality of heating element sections may be configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the plurality of heating element sections are separated from each other around a perimeter of the conduit. A separation between adjacent ones of the plurality of heating element sections around the perimeter of the conduit may be substantially equal to a separation between adjacent ones of the first, second and third conductors around the perimeter of the conduit.

The conduit may comprise a tube. The tube may have a central axis coincident with the central axis of the conduit. The tube may be of a generally circular shape at a cross-section of the electrical heater along a plane normal to the central axis of the conduit. Each of the first, second and third conductors may comprise an arc concentric with the conduit. A central angle of the arc may be at least 90 degrees. The electrical heating element may be of a tubular shape. The electrical heating element may be of a generally circular shape at a cross-section of the electrical heater along a plane normal to the central axis of the conduit.

One or more of the first, second, third and fourth conductors may comprise aluminium or aluminium alloy. One or more of the first, second, third and fourth conductors may be made of aluminium or aluminium alloy.

The electrical heating element may have a positive temperature coefficient of resistance. This means that when the electrical heater gets hotter, the resistance of the electrical heating element increases. Subsequently, the current flowing within the electrical heater and through the electrical heating element is reduced, causing the temperature of the electrical heater to reduce in a corresponding manner. In this way, the electrical heater self-regulates its temperature, and overheating or burn-out of the electrical heater by the heat generated by itself is effectively prevented, thereby improving the safety of the electrical heater.

The electrically heated conduit may further comprise an insulating jacket disposed around the electrical heater.

The insulating jacket may be electrically insulating and thermally insulating. The insulating jacket is advantageous for reducing heat dissipated from the electrically heated conduit to its surroundings, thereby improving the energy efficiency of the electrically heated conduit. The insulating jacket may comprise at least one layer of material. The insulating jacket may comprise at least one layer which is principally selected for its electrical insulating characteristics and at least one further layer which is principally selected for its thermal insulating characteristics.

The conduit may be formed by connecting a plurality of conduit sections.

The electrical heating element may comprise a plurality of heating element segments spaced apart from each other along the length of the conduit.

Each heating element segment may surround a respective conduit section.

Each heating element segment may be of a tubular shape.

Each heating element segment may comprise a plurality of heating element sections which are spaced apart from each other around a perimeter of the conduit.

Each heating element segment may have a length shorter than that of each conduit section. Each heating element segment may not cover an end region of a respective conduit section.

The fourth conductor may substantially surround the conduit. The fourth conductor may surround at least 75% of an outer surface of the conduit.

The fourth conductor may be of a tubular shape. The fourth conductor may be of a generally circular shape at a cross-section of the electrical heater along a plane normal to the central axis of the conduit.

The fourth conductor may comprise a plurality of conductor sections which are spaced apart from each other.

The plurality of conductor sections may be electrically connected in use.

The plurality of conductor sections may be configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the plurality of conductor sections are separated from each other around a perimeter of the conduit. A separation between adjacent ones of the plurality of conductor sections around the perimeter of the conduit may be substantially equal to a separation between adjacent ones of the first, second and third conductors around the perimeter of the conduit.

The plurality of conductor sections may be electrically coupled to the first, second, and third conductors, respectively, via the electrical heating element.

Each of the plurality of conductor sections may have a shape matching that of a respective one of the first, second, and third conductors. Each of the plurality of conductor sections may be aligned with a respective one of the first, second, and third conductors along a radial direction of the conduit.

According to a second aspect of the invention, there is provided a method of installing an electrical heater around a conduit for conveying fluid, the conduit having a length. The method comprises: providing first, second, and third conductors; providing a fourth conductor around the conduit; and providing an electrical heating element, wherein each of the first, second and third conductors extends along the length of the conduit, and the fourth conductor extends along the length of the conduit, and wherein the electrical heating element is disposed between the fourth conductor and the first, second and third conductors, and is arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors.

The fourth conductor may substantially surround the conduit. The fourth conductor may surround at least 75% of an outer surface of the conduit. Providing a fourth conductor around the conduit may comprise disposing the fourth conductor around the conduit. Disposing the fourth conductor around the conduit may further comprise wrapping a layer of electrically conductive material around the conduit to substantially surround the conduit, the wrapped layer of electrically conductive material forming the fourth conductor.

The layer of electrically conductive material may be wrapped helically around the conduit to substantially surround the conduit. A first adhesive layer may be provided on a side of the layer of electrically conductive material. The first adhesive layer may be electrically conductive.

Providing an electrical heating element may comprise disposing the electrical heating element around the conduit. Disposing the electrical heating element around the conduit may further comprise wrapping a layer of electrical heating material around the conduit, the wrapped layer of electrical heating material forming the electrical heating element.

The layer of electrical heating material may be wrapped helically around the conduit.

The wrapped layer of electrical heating material may substantially surround the conduit.

A second adhesive layer may be provided on a side of the layer of electrical heating material. The second adhesive layer may be electrically conductive.

The layer of electrical heating material may be formed by extrusion.

Providing first, second, and third conductors may comprise spraying electrically conductive material along the length of the conduit, the sprayed electrically conductive material forming the first, second, and third conductors.

According to a third aspect of the invention, there is provided a method of making an electrically heated conduit, the method comprising: providing a plurality of electrically heated conduit sections; wherein each electrically heated conduit section comprises a conduit section having a length; first, second, and third conductors, each of which extends along the length of the conduit section; a fourth conductor disposed around the conduit section and extending along the length of the conduit section; and an electrical heating element disposed between the fourth conductor and the first, second and third conductors, the electrical heating element being arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors; connecting the conduit sections of the plurality of electrically heated conduit sections to provide a conduit; and electrically connecting the first, second, third and fourth conductors of each electrically heated conduit section to corresponding conductors of its neighbouring electrically heated conduit sections. Each of the plurality of electrically heated conduit sections may be made using a method according to the second aspect of the invention. Connecting the conduit sections may comprise welding the conduit sections.

Electrically connecting the first, second, third and fourth conductors may comprise spraying an electrically conductive material between corresponding conductors of adjacent electrically heated conduit sections.

According to a fourth aspect of the invention, there is provided an electrical heater, the electrical heater being elongated and having a length, the heater being configurable, in use, such that the length of the heater extends along a length of an object to be heated, the electrical heater comprising: first, second, and third conductors for connecting to a three- phase power supply; a fourth conductor; and an electrical heating element disposed between the fourth conductor and the first, second and third conductors, the electrical heating element being arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors. The expression "the length of the heater extends along a length of an object to be heated" is not intended to mean that the lengths of the heater and the object must be exactly the same. The expression is also not intended to mean that the heater and the object must extend in directions which are strictly parallel to each other. For example, the electrical heater may be wound around the object helically such that the length of the heater extends generally along, but not precisely parallel to the length of the object.

Each of the first, second, third and fourth conductors may be elongated and may have a length. Each of the first, second, third and fourth conductors may be configurable, in use, such that the length of the respective conductor extends along a length of the object.

The electrical heating element may be elongated and may have a length. The electrical heating element may be configurable, in use, such that the length of the electrical heating element extends along a length of the object. The electrical heater may be flexible. The electrical heater may have an outer profile which, in use, is conformed to at least a part of an outer profile of an object to be heated.

The electrical heater may be suitable for use with a conduit for conveying fluid, the conduit having a length.

Each of the first, second, and third conductors may be configurable, in use, to extend along the length of the conduit. The fourth conductor may be configurable, in use, to be disposed around the conduit and to extend along the length of the conduit such that the fourth conductor substantially surrounds the conduit.

The electrical heating element may comprise a first surface and a second surface opposite to the first surface. The first, second, and third conductors may be disposed on the first surface. The fourth conductor may be disposed on the second surface.

The electrical heater may be a three-phase electrical heater connected in a wye configuration, with the fourth conductor being a wye point of the wye configuration.

The electrical heater may be suitable for heating an object. The fourth conductor may cover a surface of the object. The fourth conductor may be configurable to, in use, distribute heat generated by the electrical heater on the surface of the object.

Features described above with reference to the first aspect of the invention may be combined with the second, third and fourth aspects of the invention.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 schematically illustrates a perspective view of an electrically heated conduit according to an embodiment of the invention;

Figure 2 schematically illustrates a cross-sectional view of the electrically heated conduit of Figure 1 ;

Figure 3 schematically illustrates a cross-sectional view of an electrical heater of the electrically heated conduit of Figure 1 ; Figure 4 illustrates a schematic circuit diagram of electrical connections within the electrically heated conduit of Figure 1.

Figure 5 illustrates a simplified schematic circuit diagram based upon the circuit diagram of Figure 4.

Figure 6 is a schematic illustration of processing steps for manufacturing the electrically heated conduit according to Figure 1.

Figure 7 schematically illustrates a cross-sectional view of an alternative embodiment of an electrical heater.

It will be appreciated that the drawings are for illustration purposes only and are not drawn to scale. Figure 1 illustrates an electrically heated conduit 100. The electrically heated conduit 100 includes a conduit 300. The conduit 300 comprises a tube and has a tubular wall surrounding a hollow centre 200 for conveying fluid, such as, crude oil or water, etc. The tubular wall of the conduit 300 is made of, for example, steel. The conduit 300 extends along an axis V. The axis V is a central axis of the conduit 300. In the following description, the expression of "extending along a length of the conduit" is deemed as equivalent to "extending along the axis V". In a typical large-scale application which requires long-distance pipeline transport, the diameter of the conduit 300 may be at least 254 millimetres (mm). In an example, the diameter of the conduit 300 is around 305mm and the thickness of the tubular wall of the conduit 300 is around 10mm to 20mm. Figure 2 illustrates a cross-sectional view of the electrically heated conduit 100 along a plane (virtual plane, not shown) perpendicular to the axis V. As shown in Figure 2, the conduit 300 has a circular cross-sectional shape and is covered by an electrically insulating layer 6. The electrically insulating layer 6 coats an entire outer surface of the conduit 300. The electrically insulating layer 6 is provided to protect the conduit 300 from corrosion and also to electrically insulate the conduit 300 from its surroundings. The layer 6 may be made of, but not limited to, an electrically insulating polymer (such as, an electrically insulating thermoplastic polymer).

The electrically insulating layer 6 is further surrounded by a conductor 4 (also referred to as the "fourth conductor 4"). The electrically insulating layer 6 therefore serves to electrically isolate the fourth conductor 4 from the tubular wall of the conduit 300. As shown in Figure 2, each of the electrically insulating layer 6 and the fourth conductor 4 extends continuously around a perimeter of the conduit 300 and has a uniform thickness along a radial direction R of the conduit 300. Each of the electrically insulating layer 6 and the fourth conductor 4 is of a tubular shape surrounding an entire outer surface of the conduit 300. The layer 6 may have a thickness of around 2mm to 3mm, and the fourth conductor 4 may have a thickness of around 2mm to 3mm. It will be appreciated that since the conduit 300 has a circular cross- sectional shape, the expression "around the perimeter of the conduit 300" may be used interchangeably with the expression "around the circumference of the conduit 300".

The fourth conductor 4 is surrounded by an electrical heating element 5 (hereinafter, "the heating element 5"). As shown in Figure 2, the heating element 5 extends continuously around the perimeter of the conduit 300 and has a uniform thickness along the radial direction R of the conduit 300. The heating element 5 is of a tubular shape surrounding the outer surface of the conduit 300. As is further shown in Figure 2, each of the fourth conductor 4 and the heating element 5 has a circular cross-sectional shape. The heating element 5 is further surrounded by conductors 1 , 2, 3 (also referred to as "the first conductor 1", "the second conductor 2" and "the third conductor 3"). Each of the conductors 1 , 2, 3 extends along a direction parallel to the central axis V, such that, each of the conductors 1 , 2, 3 is aligned with the central axis V and a length of each conductor is substantially equal to a length of the conduit 300. In other words, the cross-sectional view as shown in Figure 2 remains the same at each point along the length of the electrically heated conduit 100. The conductors 1 , 2, 3 remain separated from each other and are not directly shorted to each other at any point along the length of the conduit 300. It will be appreciated that the electrically heated conduit 100 may comprise a connection region for connecting one or more of the conductors 1 , 2, 3 to a power supply. The connection region may be provided at an end of the electrically heated conduit 100. At the connection region, it will be appreciated the conductors 1 , 2, 3 may extend beyond the conduit 300 to connect to the power supply, or may be connected to the power supply in any convenient way. The conductors 1 , 2, 3, 4 are made of aluminium or aluminium alloy. The alloying elements typically include silicon, iron, etc. Examples of aluminium alloys for the conductors 1 , 2, 3 include Alloy 1350 and Alloy 1370, which provide a purity of 99.5% and 99.7% of aluminium, respectively. The heating element 5 is electrically conductive and has a resistivity larger than that of the conductors 1 , 2, 3, 4. In an example, the heating element 5 is made of a polymer material. The polymer material may be formed as a compound of an electrically-insulating polymer (such as, an insulating thermoplastic polymer) and an electrically-conductive filler material. One example of the electrically-insulating polymer is polypropylene or polyethylene. The electrically-conductive filler material may be carbon black. Other material, such as, carbon fibres, carbon nanotubes, graphene, graphite, metal coated fibres, metal powders or metal strand may also be used as the filler material, either alone or in combination. By blending the electrically-conductive filler material into the electrically- insulating polymer, the polymer material of the heating element 5 is configured to have a conductivity between that of the electrically-insulating polymer and that of the electrically- conductive filler material. In this way, the heating element 5 achieves a much larger resistivity than that of the conductors 1 , 2, 3, 4.

The heating element 5 may have a thickness of around 5mm to 6mm and the conductors 1 , 2, 3 may have a thickness of around 2mm to 3mm, along the radial direction R of the conduit 300.

As shown in Figure 1 , the conduit 300 has a length L along the axis V. The length L may typically be in the range of hundreds of metres to thousands of kilometres. The conduit 300 may typically be made by connecting a plurality of conduit sections together. Each conduit section may have a length of, for example, 12 metres or 24 metres. Adjacent conduit sections may typically be welded together end to end to form a conduit of a substantial length. It will be appreciated that conduit sections may be joined by other techniques, such as, by using nuts and bolts or the like. Each conduit section may be separately manufactured with a layer 6, conductors 1 , 2, 3, 4 and a heating element 5 arranged in the sectional configuration as shown in Figures 2 and 3, before the conduit sections are joined together (as described below with reference to Figure 6). After the conduit sections are joined together, the conductors 1 , 2, 3, 4 of each conduit section are electrically connected to the corresponding conductors of neighbouring conduit sections. In this way, each of the conductors 1 , 2, 3, 4 has a continuous electrical path extending along the length L of the conduit 300. However, the heating element 5 of each conduit section may not be in direct contact with that of adjacent conduit sections. For example, the heating element 5 of each conduit section may have a length of around 11 metres or 23 metres along the axis V, leaving an empty region of, for example, around 0.5 metre to each end of the respective conduit section. That is, the heating element of the conduit 300 may include tube-shaped heating element segments which are spaced apart from each other along the axis V and may not cover an entire outer surface of the conduit 300. This arrangement is useful for exposing the end regions of the fourth conductor 4 surrounding each conduit section and for facilitating an electrical connection being made between the fourth conductors of adjacent conduit sections.

The conductors 1 , 2, 3, 4 and the heating element 5 collectively provide an electrical heater 800 for heating the contents contained within the hollow centre 200 of the conduit 300. The electrical heater 800 has an elongated shape and extends along the axis V of the conduit 300. The electrical heater 800 is described below in more detail with reference to Figure 3.

The conductors 1 , 2, 3 are further coated by an insulating jacket 13. The insulating jacket 13 protects the electrically heated conduit 100 from ingress of water, dirt, etc., and electrically insulates the electrically heated conduit 100 from its surroundings. Further, the insulating jacket 13 also has good thermal insulating characteristics, and is therefore also beneficial for reducing heat dissipated from the electrically heated conduit 100 to its surroundings, thereby improving the energy efficiency of the electrically heated conduit 100. In an example, the insulating jacket 13 is made of poly-urethane foam (PUF), and has a thickness of around 50mm to 60mm. It will be appreciated that the insulating jacket 13 can be made of any suitable material which has good electrically insulating and thermally insulating characteristics, and is not limited to PUF. Further, it will be appreciated that the insulating jacket 13 can be made of more than two layers. For example, each layer may be made of a material distinct from that of the other layer(s). The layers of the insulating jacket 13 may include at least one layer which is principally selected for its good electrical insulating characteristics and at least one further layer which is principally selected for its good thermal insulating characteristics.

Figure 3 is a partial cross-sectional view of the electrically heated conduit 100 along a plane (virtual plane, not shown) normal to the axis V. As shown in Figure 3, the heating element 5 has a thickness T along the radial direction R of the conduit 300. Each of the conductors 1 , 2, 3 has a dimension (or width) W around the perimeter of the heating element 5. Further, the conductors 1 , 2, 3 are spaced apart from each other around the perimeter of the heating element 5. In particular, the first conductor 1 is separated from the second conductor 2 by a gap 10, and is separated from the third conductor 3 by a gap 12. The second conductor 2 is separated from the third conductor 3 by a gap 11. Each of the gaps 10, 1 1 , 12 has a dimension (or width) G around the perimeter of the conduit 300. The dimension G remains substantially constant along the length of the conduit 300. That is, the separation between adjacent ones of the conductors 1 , 2, 3 remains substantially constant along the length of the conduit 300. In this way, the electrical performance (as described in more detail below) of the electrical heater 800 is substantially uniform along the length of the conduit 300.

In this embodiment, the heating element 5 is coaxial with the conduit 300 and it will be understood that the direction around the perimeter of the heating element 5 is equivalent to the direction around the perimeter of the conduit 300. Therefore, the expression "around the perimeter of the heating element 5" may be used interchangeably with the expression "around the perimeter of the conduit 300". The heating element 5 electrically couples each of the conductors 1 , 2, 3 to the fourth conductor 4. For the ease of description, the heating element 5 is virtually divided to a plurality of arcuate sections 5-1 to 5-6 around the perimeter of the conduit 300 as shown in Figure 3. The central angles of the arcuate sections 5-1 to 5-6 are denoted as Θ1 to Θ6, respectively. As the arcuate sections 5-1 to 5-6 collectively form a continuous loop around the conduit 300, a sum of the central angles Θ1 to Θ6 is accordingly 360 degrees. In the embodiment illustrated by Figure 3, the central angles Θ1 to Θ3 are equal to each other, and the central angles Θ4 to Θ6 are equal to each other. Accordingly, the arcuate sections 5-1 to 5-3 are of the same dimension (or width) around the perimeter of the conduit 300. Similarly, the arcuate sections 5-4 to 5-6 are of the same dimension (or width) around the perimeter of the conduit 300. It will be appreciated that the width of each of the arcuate sections 5-1 to 5- 3 is equal to the width W of the conductors 1 , 2, 3, and that the width of each of the arcuate sections 5-4 to 5-6 is equal to the width G of the gaps 10, 11 , 12. For the ease of description, the fourth conductor 4 is virtually divided to a plurality of conductor sections 4-1 to 4-6 around the perimeter of the conduit 300 as shown in Figure 3. The central angles of the conductor sections 4-1 to 4-6 are Θ1 to Θ6, respectively.

As shown in Figure 3, the arcuate section 5-1 is sandwiched between the first conductor 1 and the fourth conductor 4, and electrically couples the first conductor 1 to the fourth conductor 4. Two ends of the arcuate section 5-1 are aligned with two ends of the first conductor 1 around the perimeter of the conduit 300. That is, the central angle of the first conductor 1 is the same as the central angle Θ1 of the arcuate section 5-1. Likewise, the arcuate section 5-2 electrically couples the second conductor 2 to the fourth conductor 4, and the arcuate section 5-3 electrically couples the third conductor 3 to the fourth conductor 4. The central angle of the second conductor 2 is the same as the central angle Θ2 of the arcuate section 5-2, and the central angle of the third conductor 3 is the same as the central angle Θ3 of the arcuate section 5-3. The dimensions (or widths) of the conductors 1 , 2, 3 around the perimeter of the conduit 300 are equal to each other. Further, since the separations (i.e., the width G) between adjacent ones of the conductors 1 , 2, 3 are equal to each other, the conductors 1 , 2, 3 therefore are evenly spaced apart from each other around the perimeter of the conduit 300.

The arcuate section 5-4 is between the arcuate sections 5-1 , 5-2. Therefore the arcuate section 5-4 provides a direct electrical pathway between the first and second conductors 1 , 2 which does not pass via the fourth conductor 4. Likewise, the arcuate section 5-5, which is between the arcuate sections 5-2, 5-3, provides a direct electrical pathway between the second and third conductors 2, 3, and the arcuate section 5-6, which is between the arcuate sections 5-1 , 5-3, provides a direct electrical pathway between the first and third conductors 1 , 3. Given that the arcuate sections 5-4 to 5-6 have the same width G, the direct electrical couplings between adjacent ones of the conductors 1 , 2, 3 (not via the fourth conductor 4) are equal to each other.

Figure 4 illustrates a schematic circuit diagram of electrical connections within the electrical heater 800 of the electrically heated conduit 100. Each of the resistors R1 , R2, R3 denotes the equivalent resistance of an electrical pathway between a respective one of the conductors 1 , 2, 3 and the fourth conductor 4 via the heating element 5. Each of the resistors R4, R5, R6 denotes the equivalent resistance of a direct electrical pathway between adjacent ones of the conductors 1 , 2, 3 via the heating element 5 without passing via the fourth conductor 4. Since the heating element 5 has a much larger resistivity than that of the conductors 1 , 2, 3, 4, for simplicity, the resistances of the conductors 1 , 2, 3, 4 themselves are neglected and the resistances of R1 to R6 are treated as resulting from the resistance of the heating element 5 alone (in particular, the resistances of the arcuate sections 5-1 to 5-6).

The cross section of each of the arcuate sections 5-1 to 5-6 can be approximated to a rectangle, which has a length equal to the width of the respective arcuate section around the perimeter of the conduit 300, and a width equal to the thickness of the respective arcuate section along the radial direction R of the conduit 300. Therefore, according to Ohm's law, the resistance of R1 is calculated following Equation (1) below.

T

In Equation (1), p is the resistivity of the heating element 5 (assuming that the heating element 5 has a uniform resistivity); T is the thickness of the heating element 5 along the radial direction R of the conduit 300; W is the width of the arcuate section 5-1 around the perimeter of the conduit 300; and L is the length of the arcuate section 5-1 along the length of the conduit 300. It will be understood that the length of the arcuate section 5-1 is equal to that of the arcuate sections 5-2 to 5-6, and is further equal to the circuit length of the electrical heater 800. Since the arcuate sections 5-1 to 5-3 have the same width W, each of R2 and R3 has a resistance equal to that of R1.

Similarly, the resistance of R4 can be calculated following Equation (2) below. In Equation (2), G is the width of the arcuate section 5-4 around the perimeter of the conduit 300. Since the arcuate sections 5-4 to 5-6 have the same width G, each of R5 and R6 has a resistance equal to that of R4.

By comparing the resistances of R1 and R4, it is derived that:

R4 W x G

Rl ^~ T²

(3)

Typically, each of the widths W and G is much larger than the thickness T of the heating element 5. In the example described above where the diameter of the conduit 300 is around 305mm, the thickness T of the heating element is around 6mm, the width W of each of the arcuate sections 5-1 to 5-3 is around 300mm, and the width G of each of the arcuate sections 5-4 to 5-6 is around 25mm to 30mm. Accordingly, the resistance of each of the resistors R4, R5, R6 is around 578 times the resistance of each of the resistors R1 , R2, R3 in this example. That is, the electrical coupling between each of the conductors 1 , 2, 3 and the fourth conductor 4 is much stronger than the direct electrical coupling between adjacent ones of the conductors 1 , 2, 3 which does not pass via the fourth conductor 4. Therefore, when any two of the conductors 1 , 2, 3 are connected to a power supply, a majority of the electrical current tends to flow through a pathway with the strongest electrical coupling and the least electrical resistance, i.e., a pathway from one of the conductors 1 , 2, 3, via the heating element 5 to the fourth conductor 4, and back to another of the conductors 1 , 2, 3 via the heating element 5 again. For simplicity, the electrical pathways formed by the resistors R4, R5, R6 is therefore neglected such that only the electrical pathways formed by the resistors R1 , R2, R3 remain, as shown in the simplified circuit diagram of Figure 5.

As illustrated in Figure 5, the conductors 1 , 2, 3 are electrically coupled to the fourth conductor 4, via the resistors R1 , R2, R3. In this way, the electrical heater 800 is effectively connected in a wye configuration (also called "star configuration"), with the fourth conductor 4 being the wye point (also called "star point"). Each of the conductors 1 , 2, 3 is electrically connected to the wye point via a respective arcuate section of the heating element 5, forming three phases of the electrical heater 800. Therefore, the conductors 1 , 2, 3 are suitable for connection with a three-phase electric power supply, and the electrical heater 800 can be used as a three-phase electrical heater. Further, since the resistances of R1 , R2, R3 are equal to each other, the electrical heater 800 has electrically conductive pathways with equal resistance across the three phases and accordingly will draw equal currents from each phase of a three-phase power supply when the conductors 1 , 2, 3 are connected to the three-phase electric power supply. Therefore, the three phases of the electrical heater 800 are balanced.

It will be appreciated that the schematic circuit diagrams shown in Figures 4 and 5 are merely employed to assist the explanation on the operational principles of the electrical heater 800, and are not intended for use as precise models of the electrical connections within the electrical heater 800.

In use, the conductors 1 , 2, 3 are connected to the three output phases of a three-phase power supply (not shown), respectively. Generally, the fourth conductor (i.e., the wye point) is connected to the earth ground and acts as a neutral return in use. An electric current flows out of the power supply, through each of conductors 1 , 2, 3 to a different one of conductors 1 , 2, 3 via a path consisting of two of the resistors R1 , R2, R3 and the fourth conductor 4, and further flows back to the power supply. According to Joule's first law, the passage of an electric current through an electrical resistor produces heat, and the power of heating is proportional to the resistance of the resistor and the square of the current. As described above, the resistors R1 , R2, R3 result from the arcuate sections 5-1 to 5-3 of the heating element 5, which has a much larger resistance than that of the conductors 1 , 2, 3, 4. Therefore, heat generated by the conductors 1 , 2, 3, 4 is negligible compared to heat generated by the resistors R1 , R2, R3 which result from the heating element 5. That is, the heating element 5 (in particular, the arcuate sections 5-1 to 5-3) generates a majority of the heat output by the electrical heater 800. Therefore, the arcuate sections 5-1 to 5-3 form an active heat generation region of the electrical heater 800. The heat generated by the heating element 5 is transmitted, through the fourth conductor 4, the electrically insulating layer 6 and the tubular wall of the conduit 300, to the contents of the conduit 300. As described above, the fourth conductor 4 is made of aluminium or aluminium alloy. Aluminium is a good electrical conductor as well as a good thermal conductor. The fourth conductor 4 is of a tubular shape and surrounds an entire outer surface of the conduit 300. Therefore, in addition to serving as the wye point of the electrical heater 800, the fourth conductor 4 also serves as a heat distributor for distributing the heat generated by the heating element 5 around the conduit. With the fourth conductor 4, the electrical heater 800 can heat up the contents of the conduit 300 substantially evenly around a circumferential surface of the conduit 300.

It has further been found that by using the fourth conductor 4 to distribute heat around the conduit 300, the heating element 5 is generally required to be heated to a temperature which is lower than its required temperature in a scenario where the fourth conductor is not provided (i.e., the heat generated by the heating element 5 is confined within discrete portion(s) of the conduit 300), in order to maintain a temperature of the contents of the conduit 300. Therefore, with the fourth conductor 4, the electrical heater 800 may be more energy efficient in maintaining a uniform temperature of the contents of the conduit 300. The electrical heater 800 described above typically achieves a circuit length of around 30 to 40 kilometres when connected to a three-phase power supply which supplies a root-means- square (rms) voltage of around 1040V across any two phases, and provides a power output of around 30 Watt per metre length (30W/m). If the conduit 300 is required to have a length of longer than the circuit length of the electrical heater 800, then more than one electrical heater 800 may be separately provided along the length of the conduit 300. It will be understood that each electrical heater 800 requires a power supply, and therefore the electrically heated conduit 100 requires the provision of a power supply approximately every 30 to 40 kilometres. Figure 6 illustrate a process of manufacturing the electrically heated conduit 100. In step S1 , a conduit is provided. The conduit may be the conduit 300, or may be a conduit section of the conduit 300 and have a length of, for example, 12 metres or 24 metres.

In step S2, the electrically insulating layer 6 is disposed around the conduit. In an example, the electrically insulating layer 6 is extruded over and around the conduit to cover an entire outer surface of the conduit. It will be understood that if the conduit provided in step S1 already includes an electrically insulating layer, then the step S2 can be omitted.

Steps S3 to S6 illustrate a process 400 of manufacturing the electrical heater 800. In step S3, the fourth conductor 4 is disposed around the conduit. In an example, an aluminium layer (such as, a layer of aluminium alloy) is used to form the fourth conductor 4. The aluminium layer has a thickness of around 2mm to 3mm, corresponding to a desired thickness of the fourth conductor 4. The aluminium layer may have a width of the order of tens of centimetres and have a length sufficient for covering the conduit provided in step S1. The aluminium layer may be wrapped continuously around the conduit following a helical pattern. The width of the aluminium layer is generally greater than the pitch of the helical pattern. That is, adjacent portions of the aluminium layer along the length of the conduit overlaps with each other, such that the wrapped aluminium layer forms a tube with a continuous side wall without any substantial void or gap. Alternatively, at least two aluminium layers may be aligned with the central axis of the conduit, with the edges of the layers joined together to form a tube surrounding the conduit. In another example, the fourth conductor 4 may be disposed around the conduit by spraying electrically conductive material.

One or each side of the aluminium layer may be optionally provided with an adhesive layer. An adhesive layer on the inner side of the aluminium layer may be beneficial for securing the aluminium layer to the conduit (in particular, the surface of the electrically insulating layer 6) and is also beneficial for securing overlapping portions of the aluminium layer in order to form a tube surrounding the conduit. An adhesive layer on the outer side of the aluminium layer may be beneficial for bonding the aluminium layer to the heating element 5. The adhesive layers are made of an electrically conductive material to improve the conductivity of the wrapped aluminium layer and to improve the electrical connection between the heating element 5 and the aluminium layer.

It will be appreciated that the aluminium layer may be disposed around the conduit in any suitable manner other than the example described above. For example, the aluminium layer may be wrapped around the conduit to form a plurality of rings and adjacent rings partially overlap with each other to form a tube surrounding the conduit.

It will further be appreciated that a layer of electronically conductive material other than aluminium or aluminium alloy may be used to form the fourth conductor 4.

In step S4, the heating element 5 is disposed around the conduit. In an example, a sheet extrusion process is employed to extrude a sheet of electrical heating material. The electrical heating material may be a polymer material which is formed as a compound of an electrically-insulating polymer and an electrically-conductive filler material as described above. The extruded sheet has a thickness of around 5mm to 6mm, corresponding to a desired thickness of the heating element 5. The extruded sheet may have a width of around 300mm. The extruded sheet may typically have a length of 500 to 2000 metres, but may be cut to length to suit the size of the conduit provided in step S1. Subsequently, the extruded sheet of electrical heating material is disposed around the conduit to form the heating element 5. In an example, the extruded sheet is wrapped continuously around the conduit following a helical pattern. The pitch of the helical pattern is less than the width of the extrude sheet. That is, adjacent portions of the extruded sheet along the length of the conduit overlaps with each other, such that the wrapped sheet forms a tube with a continuous side wall (i.e., without any substantial void or gap) to surround the conduit.

One or each side of the extruded sheet may be optionally provided with an adhesive layer. An adhesive layer on the inner side of the extruded sheet may be beneficial for securing the extruded sheet to the conduit (in particular, the fourth conductor 4) and may also be also beneficial for securing overlapping parts of the extruded sheet in order to form a tube surrounding the conduit. An adhesive layer on the outer side of the extruded sheet may be beneficial for bonding the extruded sheet to the conductors 1 , 2, 3. The adhesive layers are made of an electrically conductive material. Where an adhesive layer is provided, the adhesive layer may be considered to form an intermediate layer between the heating element 5 and the fourth conductor 4.

It will be appreciated that alternative methods may be employed to dispose the heating element 5 around the conduit. For example, more than one extruded sheet of electrical heating material may be aligned with the central axis of the conduit, with their edges joined together to form a tube surrounding the conduit.

As described above, in the event that the conduit provided in step S1 is a conduit section of the conduit 300, the extruded sheet may not cover an entire outer surface of the conduit. In particular, the extruded sheet may leave an empty region of, for example, around 0.5 metre to each end of the conduit along the central axis of the conduit.

In step S5, the conductors 1 , 2, 3 are provided. In an example, the conductors 1 , 2, 3 are formed by spraying electrically conductive material (e.g., aluminium) on the outer surface of the heating element 5 along the length of the conduit. The spraying process is controlled to achieve a desired width and thickness for each of the conductors 1 , 2, 3. For example, a mask may be used during the spraying process to define boundaries (in particular, the width) of the conductors 1 , 2, 3. Further, the thickness of the conductors 1 , 2, 3 may be monitored such that the spraying process is terminated after the thickness of the conductors 1 , 2, 3 reaches a predetermined value.

In the process 400 of manufacturing the electrical heater 800 as described above, the fourth conductor 4, the heating element 5 and the conductors 1 , 2, 3 are disposed around the conduit layer by layer.

An alternative process 400 may be used for manufacturing the electrical heater 800. In the alternative process, the fourth conductor 4, the heating element 5 and the conductors 1 , 2, 3 are stacked to form a laminated structure which is separate from the conduit provided in step S1. The laminated structure may be substantially planar. Subsequently, the laminated structure is disposed around the conduit to form the electrical heater 800. It will be understood that the laminated structure has a thickness of around 10mm corresponding to the thickness of the electrical heater 800 along the radial direction R and a width of around 1 metre corresponding to a perimeter of the conduit, and may have a length corresponding to the length of the conduit. The laminated structure is flexible due to its thin thickness and inherent flexibility of the constituent materials and therefore can be easily bent to conform to the circular profile of the conduit. It will be appreciated that due to its flexible nature, the electrical heater 800 made in this way can have an outer profile conforming to at least a part of any outer profile of an object to be heated.

In the event that the conduit 300 comprises a plurality of conduit sections, the process 400 is repeatedly carried out on each conduit section. Subsequently, the conduit sections may be transported to a site of application and joined end to end on site. After the conduit sections are joined together, the conductors 1 , 2, 3, 4 of each conduit section are then electrically connected to the respective conductors of adjacent conduit sections. This may be done by connecting the corresponding conductors using electrically conductive tapes (which comprise, for example, aluminium or aluminium alloy). The conductor 4 of each conduit section may also be connected by spraying electrically conductive material (such as, aluminium or aluminium alloy) at the joint of adjacent conduit sections. It will be appreciated that alternative methods may be employed to electrically connect the corresponding conductors of adjacent conduit sections.

In step S6, the insulating jacket 13 is disposed around the conduit 300, in particular to cover the conductors 1 , 2, 3. The insulating jacket 13 may be disposed using any suitable techniques, such as, but not limited to, extrusion.

It will be appreciated that the fourth conductor 4 may be made of any suitable material which is electrically conducting as well as thermally conducting and is not limited to aluminium or aluminium alloy. For example, the fourth conductor 4 may be made of metal (such as copper or the like), or may be made of carbon based materials (such as, but not limited to, graphene, carbon nanotubes, etc.). Further, the conductors 1 , 2, 3 may be made of other electrically conductive material (such as, for example, copper), and is not limited to aluminium or aluminium alloy. It will be understood that preferably, the material of the conductors 1 , 2, 3 has a low electrical resistivity so as to reduce the amount of voltage drop along the conductors, thereby allowing the electrical heater 800 to achieve a relatively long circuit length.

It will further be understood that the heating element 5 may be made of any suitable material which is electrically conductive and has an electrical resistivity larger than that of the conductors 1 , 2, 3, 4, and is not limited to the polymer material described above. It will however be appreciated that the heating element 5 formed as a compound of an electrically- insulating polymer and an electrically-conductive filler material has a positive temperature coefficient of resistance. That is, the electrical resistance of the heating element 5 increases with the temperature of the heating element 5. This is generally desirable for reasons of safety. When the electrical heater 800 gets hotter, the resistance of the heating element 5 increases. Subsequently, the current flowing within the electrical heater 800 is reduced, causing the temperature of the electrical heater 800 to reduce in a corresponding manner. In this way, the electrical heater 800 self-regulates its temperature, and overheating or burn-out of the electrical heater 800 by the heat generated by itself is effectively prevented, thereby improving the safety of the electrical heater 800. Further, it will be appreciated that the heating element 5 may have a different temperature coefficient of resistance characteristics from that described above. For example, the heating element 5 may be made of a blended material having negative temperature coefficient of resistance when the temperature is low and having positive temperature coefficient of resistance when the temperature is high. An example of the blended material is described in WO 2007/132256 A1 , which is herein incorporated by reference.

As illustrated in Figure 2, the conductors 1 , 2, 3 have the same width W around the perimeter of the conduit 300. It will be appreciated that this is not necessary. It is however preferable that the conductors 1 , 2, 3 have equal widths to ensure that the electrical heater 800 is balanced. Any imbalance across the three phases of the electrical heater 800 reduces the efficiency of the electrical heater 800, and is also undesirable for the stability of a three- phase power supply to which the electrical heater 800 is connected. Therefore, it is preferable that the electrical heater 800 is balanced.

Further, in the embodiment described above, the thickness of each of the conductors 1 , 2, 3, 4 is around 2mm to 3mm. Other thicknesses of the conductors 1 , 2, 3, 4 are possible and can be appropriately determined based upon the electrical resistivity of the conductors and a desired circuit length of the electrical heater 800. In particular, it will be understood that the maximum circuit length of the electrical heater 800 is affected by an amount of voltage drop per unit length of the conductors 1 , 2, 3, which is further determined by (among other parameters) the resistivity of the conductors 1 , 2, 3 and a cross-sectional area of each of the conductors 1 , 2, 3. By increasing the thickness of the conductors 1 , 2, 3, the cross-sectional area of each of the conductors 1 , 2, 3 is increased, which is beneficial for reducing the amount of voltage drop per unit length of the conductors 1 , 2, 3 and is accordingly beneficial for improving the maximum circuit length achievable by the electrical heater 800.

In the embodiment described above, the thickness T of the heating element 5 is around 5mm to 6mm, the width W of each of the conductors 1 , 2, 3 (or, the arcuate sections 5-1 to 5-3) around the perimeter of the conduit 300 is around 300mm, and the width G of each of the gaps 10, 11 , 12 (or, the arcuate sections 5-4 to 5-6) around the perimeter of the conduit 300 is around 25mm to 30mm. It will further be appreciated that other dimensions of the thickness T, widths W and G are possible. The thickness T of the heating element 5 may be determined with reference to a voltage level of a power supply to which the electrical heater 800 is connected. As indicated by Equation (1), the resistance of each of the arcuate sections 5-1 , 5-2, 5-3 is proportional to the thickness T. If the thickness T is small, the resistances of the arcuate sections 5-1 , 5-2, 5-3 are small. Accordingly, it will be understood that if the conductors 1 , 2, 3 are connected to a power supply which has a high voltage level, a large current will flow through the thin arcuate sections 5-1 , 5-2, 5-3 and there is a risk that the large current will lead to a breakdown of the heating element 5, causing malfunctions of the electrical heater 800. If the heating element 5 is made of the polymer material described above, it has been found that each millimetre of the heating element 5 may typically withstand an rms voltage of around 100V. Therefore, if the electrical heater 800 is connected to a three-phase power supply which provides an rms voltage of 1040V across any two phases (i.e., equivalent to an rms voltage of around 600V between each of the conductors 1 , 2, 3 and the fourth conductor 4), the thickness T of the heating element 5 is preferably around 6mm. It will be understood that if the electrical heater 800 is connected to a power supply outputting a lower voltage, the thickness T of the heating element 5 may be reduced.

Preferably, the width G is greater than the thickness T of the heating element 5. More preferably, the width G is at least three times the thickness T of the heating element 5. This is beneficial for directing an electrical current which flows from each of the conductors 1 , 2, 3 to follow an electrical pathway which passes via the fourth conductor 4.

As shown in Figure 3, each of the conductors 1 , 2, 3 has two edges around the perimeter of the conduit 300, with the two edges defining a central angle of the respective conductor. For example, the conductor 1 has two edges 14 and 15 around the conduit 300. Taking the edge 15 as an example, there are two electrical pathways between the conductor 1 (around the edge 15) and the conductor 3. The two electrical pathways include a first electrical pathway which passes via the arcuate section 5-1 , the fourth conductor 4 and the arcuate section 5-3, and a second electrical pathway which is on a surface of the arcuate section 5-6 around the perimeter of the conduit 300. If the width G is small, the second electrical pathway may experience high current density, and high current density is likely to cause thermal stress and early failure of the heating element 5. By arranging the width G to be at least greater than the thickness T of the heating element 5, the electrical conductivity of the second electrical pathway is reduced to a level lower than that of the first electrical pathway. Accordingly, a majority of a current flowing out of the conductor 1 tends to follow the first electrical pathway to the conductor 3. Thus, by increasing the width G, it is possible to reduce the current density along the second electrical pathway, thereby prolong the lifespan of the heating element 5. Further, by directing a majority of the current to the first electrical pathway which passes via the conductor 4, the heat distribution efficiency around the conduit 300 is enhanced. It has been found that if the width G is is at least three times the thickness T, the current flowing through the second electrical pathway is negligible compared to the current flowing through the first electrical pathway. Therefore, the lifespan of the heating element 5 and the heat distribution efficiency around the conduit 300 are further improved. Preferably, the width W of each of the conductors 1 , 2, 3 is at least around three times the width G of each of the gaps 10, 11 , 12. That is, the conductors 1 , 2, 3 cover a significant portion (i.e., larger than 75%) of the perimeter of the conduit 300. For example, as shown in Figure 2, each of the conductors 1 , 2, 3 resembles an arc concentric with the conduit 300. A central angle of the arc is at least 90 degrees.

As described above, the maximum circuit length of the electrical heater 800 is associated with the cross-sectional area of the conductors 1 , 2, 3. By arranging the conductors 1 , 2, 3 to cover a significant portion of the perimeter of the conduit 300, each of the conductors 1 , 2, 3 is allowed to have a significant dimension around the perimeter of the conduit 300, such that the thickness of the conductors 1 , 2, 3 can be reduced (for example, to around 2mm to 3mm in the embodiment described above) while a cross-sectional area of the conductors 1 , 2, 3 (and also a circuit length of the electrical heater 800) is maintained at a desired level. The thickness of the conductors 1 , 2, 3 along the radial direction R is less than, and preferably may be less than one tenth of the width W of the conductors 1 , 2, 3 around the perimeter of the conduit 300. In this way, the conductors 1 , 2, 3 form a thin "coat" covering the conduit 300 and do not substantially increase a cross-sectional size of the conduit 300. Further, the conductors 1 , 2, 3 formed in this way have a less-irregular profile which generally follows an outer profile of the conduit 300. This allows the electrically heated conduit 100 to be handled more easily, and facilitates the manufacturing and installation of the electrically heated conduit 100.

Further, by making the width W at least around three times the width G, a majority (for example, greater than 75%) of a perimeter of the conduit 300 can be directly heated up by the electrical current flowing through the arcuate sections 5-1 , 5-2, 5-3 between the fourth conductor 4 and the conductors 1 , 2, 3. This allows heat generated by the electrical heater 800 to be efficiently transferred to the contents of the conduit 300 and also facilitates heat distribution around the conduit 300.

It will further be appreciated that it is not necessary for the fourth conductor 4 to surround an entire outer surface of the conduit 300 as described in the embodiment above. The fourth conductor 4 may surround a substantial portion (preferably, more than 75%) of an outer area of the conduit 300 and still be capable of achieving satisfactory heat distribution effect around the conduit 300, although this is less ideal than the embodiment described above. There may be at least one slit or void extending through the fourth conductor 4. However it will be understood that the dimensions of the slit/void must be controlled within a limit to avoid the slit/void from substantially deterring heat distribution around the conduit 300. For example, the limit may be that an outer area of the conduit 300 which is not covered by the fourth conductor 4 should not exceed a length of 200mm and a width of a tenth of the perimeter of the conduit 300. It will be appreciated that other suitable limits may be used.

Alternatively, the fourth conductor 4 may have a structure similar to a mesh and may contain a plurality of through-holes. It will be appreciated that if the fourth conductor 4 is not continuous, the thickness of the fourth conductor 4 is preferably increased in order to maintain the conductivity of the fourth conductor 4 within an acceptable range, so as to ensure that the current carrying capability of the fourth conductor 4 (and accordingly the heat distribution effect achieved by the fourth conductor 4) does not substantially deteriorate. In a further example, the conductor sections 4-4 to 4-6 of the fourth conductor 4 as shown in Figure 3 may be omitted. That is, the fourth conductor 4 may comprise a plurality of conductor sections (i.e., the conductor sections 4-1 to 4-3) which are spaced apart from each other around the perimeter of the conduit 300. Edges of the conductor sections may be aligned to edges of the conductors 1 , 2, 3, such that a separation between adjacent conductor sections around the perimeter of the conduit 300 is substantially equal to a separation between adjacent ones of the conductors 1 , 2, 3 around the perimeter of the conduit 300. In use, each of the plurality of conductor sections are connected to the earth ground such that the plurality of conductor sections are electrically connected together to collectively act as a neutral return. The plurality of conductor sections are electrically coupled to the conductors 1 , 2, 3, respectively, via the heating element 5. When the electrical heater 800 is connected to a three-phase power supply, a phase current flows from each of the conductors 1 , 2, 3, through the heating element 5, to a respective conductor section. Each conductor section serves to distribute heat generated by a respective phase current on a part of the outer surface of the conduit 300 that is covered by the respective conductor section. The magnitudes of the three phase currents flowing through the electrical heater 800 are substantially the same because the electrical heater 800 is balanced as described above. Therefore, the parts of the outer surface of the conduit 300 that are covered by the conductor sections are heated up to the substantially same temperature. Since the conductor sections 4-1 , 4-2, 4-3 cover a substantial portion (preferably, more than 75%) of the outer surface of the conduit 300, the conductor sections are still capable of achieving satisfactory heat distribution effect around the conduit 300 without the conductor sections 4-4, 4-5, 4-6. It will further be appreciated that, in some embodiments, the conductor sections 4-1 , 4-2, 4-3 may extend to a greater or lesser extent than the corresponding conductors 1 , 2, 3. Similarly, a space, or spaces between conductor sections (e.g. a void or slit as described above) may not be aligned with, or correspond to, a particular feature of the conductors 1 , 2, 3. As described above, the electrical heater 800 is connected to a three-phase power supply for use as a three-phase electrical heater. However, it will be understood that this is not necessary. The electrical heater 800 can also function as a single-phase electrical heater. For example, any two of the conductors 1 , 2, 3 may be connected to the supply and return terminals of a single-phase power supply. In a further example, all of the conductors 1 , 2, 3 may be shorted together to form a node, and this node and the fourth conductor 4 may be connected to the supply and return terminals of a single-phase power supply. The power output of the electrical heater 800 may typically be within a range from around 30 to around 100 W/m. Thus, for a particular power supply, increasing the power output will lead to a reduction in the maximum circuit length achievable by the electrical heater 800. Using the electrical heater 800 as a three-phase electrical heater is, however, generally more preferable in industrial applications than using the electrical heater 800 as a single-phase electrical heater. In particular, three-phase electric power supplies are widely used and commonly available in large-scale applications. National grids, industrial plants, commercial sites and high-power equipment normally operate with three-phase power supplies. Further, generally speaking, a three-phase electrical heater is typically able to achieve a circuit length of several kilometres to tens of kilometres, which satisfy the length requirements to electrical heaters in large-scale applications. In contrast, a single-phase electrical heater is generally limited to a much shorter circuit length, e.g., hundreds of metres, than a three-phase electrical heater.

In more detail, assuming that an equivalent amount of power is to be output, each phase of a three-phase electrical heater only carries a third of a total current carried by a single-phase electrical heater, and accordingly an amount of voltage drop per unit length of each conductor of the three-phase electrical heater is a third of an amount of voltage drop per unit length of each conductor of the single-phase electrical heater (assuming that conductors with the same cross-sectional area are used in the single-phase and three-phase electrical heaters). A reduced voltage drop per unit length of the conductors means that the three- phase electrical heater can achieve a longer circuit length than that achievable by the single- phase electrical heater. In order to increase the circuit length of the single-phase electrical heater, more conductive material may be used to enlarge the cross-sectional area of the conductors, so as to reduce the resistance of the conductors and the amount of voltage drop on the conductors. However, this may not be cost-effective (e.g. due to the additional conductive material required), or practical (e.g. due to the mechanical properties of the enlarged conductors). Therefore, single-phase electrical heaters which have convenient conductor dimensions generally have lower efficiency than three-phase electrical heaters, and may be less preferable in large scale applications. Indeed, single-phase self-regulating heaters have many desirable characteristics for use with pipe-lines. For example, such heaters can be cut to any desired length, and are inherently temperature safe due to the self-regulating behaviour of the heating element. However, such single-phase self-regulating heaters may not be particularly suitable or convenient for use with long pipelines. Moreover, for the reasons set out above, scaling up a single-phase heater for use in a longer circuit length (e.g. by increasing the conductor cross-sectional area) may not be appropriate.

The electrical heater 800 used as a three-phase electrical heater generally has better performance than a conventional heater arrangement used to heat long pipelines. An arrangement used to heat long pipelines may typically include three separate heaters extending in parallel along the length of a conduit (e.g., the conduit 300). The three heaters may be spaced apart from each other around a periphery of the conduit, and are each provided with a conductor surrounded by a sheath of electrically insulating material. Remote ends of the three conductors are electrically connected together to form a wye point. In use, ends of the three conductors opposite to the wye point may be separately connected to three phases of a three-phase power supply, such that the conductors are configured to generate heat output due to the electrical resistance of the conductors themselves. Each of the three heaters may be referred to as a series-resistance heater. In contrast, for the electrical heater 800, it is the heating element 5, rather than the conductors 1 , 2, 3, that generates a majority of the output heat.

Although an arrangement of series resistance heaters as described above may achieve a relatively long circuit length suitable for use in large-scale applications, it cannot self-regulate its temperature in the way that the electrical heater 800 does (due to the positive temperature coefficient of resistance of the heating element 5) and therefore requires additional temperature controls to ensure temperature safety. Further, due to the fact that remote ends of the three conductors are electrically connected together, such an arrangement of (e.g. three) series resistance heaters cannot be easily cut to length in use and is normally provided for use with a conduit having a particular length. Moreover, it is often necessary to modify the design of a series resistance heater arrangement, for example, by modifying a length and/or a cross-sectional area of each conductor, in order to allow the arrangement to be used in a particular application. This is because the design of a series resistance heater is generally determined by a particular length of a conduit to be heated, a voltage level of an available power supply and/or a required level of power output. Therefore, it may be difficult to use one design of a series resistance heater (or arrangement thereof) for different applications. In contrast, the electrical heater 800 can be conveniently cut to length in use, by removing, for example, a length at a remote end of the heater 800. Further, the conductors 1 , 2, 3 of the electrical heater 800 are used for transmitting electrical power to the heating element 5, but are not used for generating heat. Therefore, as long as the resistances of the conductors 1 , 2, 3 are controlled to be relatively small, it is possible to use a particular design of the electrical heater 800 for multiple applications. As a result, the electrical heater 800 may be flexibly used for a range of different applications and needs not be redesigned for each application.

Further, for different applications where the electrical heater 800 is cut to different lengths, the electrical heater 800, when connected to the same power supply, is able to provide a substantially constant power output per unit length. This is because different parts of the heating element 5 along the length of the electrical heater 800 experience approximately the same level of voltage, since the voltage loss along the conductors 1 , 2, 3 is negligible compared to the voltage drop across the heating element 5. Therefore, the heating element 5 typically generates substantially the same amount of heat per unit length of the electrical heater 800, regardless of the total length of the electrical heater 800. In contrast, in the arrangement of series resistance heaters as described above, the conductors are used to generate heat, the length of the series resistance heaters directly and significantly affects the resistance of the conductors. It has been found that when the total length of the series resistance heaters is doubled, the power output per unit length is reduced to a quarter of the original power output per unit length.

Further, an arrangement of three series-resistance heaters described above does not include a fourth conductor (like the conductor 4), or distributed heat generating areas, both of which features contribute to allowing heat to be effectively distributed around a conduit to be heated. Consequently, there generally exists a significant progressive temperature gradient from the separate conductors (which are effectively also heating elements) of the series resistance heater arrangement to the contents of the conduit to be heated, via the sheath of each heater (which sheaths include the electrically insulating material which surrounds each of the conductors). For example, when a temperature of the conduit is heated to be around 60°C, the conductors of each of the series resistance heaters may reach a temperature of around 160°C. The temperature difference of around 100°C between the conductors and the conduit is likely to cause significant differential expansions across the conductors, the sheaths of the heaters, the conduit, and the contents of the conduit. The differential expansions must be managed to ensure safety of the series resistance heater arrangement, and the system in which it operates. Managing the differential expansions may increase the complexities of using the series resistance heaters.

The electrical heater 800 substantially reduces the temperature difference, by using the fourth conductor 4 to distribute heat generated by the heating element 5 evenly around the conduit 300. Further, the location of heat generation (i.e. throughout the arcuate sections 5-1 to 5-3 of the heating element 5) contributes further to the generated heat being effectively distributed around the conduit. It has been found that during the operation of the electrically heated conduit 100, the temperature difference between the conductors 1 , 2, 3 and the conduit 300 is typically less than 5°C. Accordingly differential expansions across different layers of the electrically heated conduit 100 are generally negligible.

As shown in Figure 2, the heating element 5 is disposed around the fourth conductor 4, and the conductors 1 , 2, 3 are further disposed around the heating element 5. That is, the fourth conductor 4, the heating element 5 and the conductors 1 , 2, 3 are disposed along a radially outward direction of the conduit 300. It will however be appreciated that an alternative embodiment is possible, where the heating element 5 is disposed around the conductors 1 , 2, 3, and the fourth conductor 4 is further disposed around the heating element 5. That is, the conductors 1 , 2, 3, the heating element 5 and the fourth conductor 4 are disposed along a radially outward direction of the conduit 300, and the fourth conductor 4 is the outermost layer of the electrical heater 800. In the alternative embodiment, the fourth conductor 4 serves as the wye point of the electrical heater 800 and is also beneficial for distributing heat generated by the heating element 5 around the conduit 300. It will be understood that in the alternative embodiment, the electrically heated conduit 100 may be manufactured using a process similar to that illustrated in Figure 6, with steps S3 and S5 swapped.

In Figure 2, the heating element 5 is in contact with the fourth conductor 4, and is further in contact with the conductors 1 , 2, 3. It will however be understood that the heating element 5 does not need to be in direct contact with the conductors 1 , 2, 3, 4. Any intermediate layer which does not substantially inhibit the electrical coupling between the heating element 5 and the conductors 1 , 2, 3, 4 may be provided. For example, one or more layers of material which have positive (or negative) temperature coefficients of resistance may be disposed between the heating element 5 and the conductors as intermediate layers.

As described above, each of the conductors 1 , 2, 3 extends along a direction parallel to the central axis V, such that, each of the conductors 1 , 2, 3 is aligned with the central axis V and a length of each conductor is substantially equal to a length of the conduit 300. This arrangement of the conductors 1 , 2, 3 is referred to as "linear arrangement" in the description below. It will be appreciated that other arrangements of the conductors 1 , 2, 3 are possible. For example, each of the conductors 1 , 2, 3 may extend helically around the conduit 300, thereby forming a triple helix. In the triple helix arrangement, the pitch of the triple helix may remain uniform along the length of the conduit 300. In any event, the dimension G of the gaps 10, 11 , 12 may remain substantially constant along the length of the conduit 300, so as to ensure that the electrical performance of the electrical heater 800 is substantially uniform along the length of the conduit 300. Alternatively, it will be appreciated that the dimension G of the gaps 10, 11 , 12 may vary along the length of the conduit 300 to deliver different levels of heat output along the length of the conduit 300.

It will further be appreciated that the linear arrangement of the conductors 1 , 2, 3 is preferable in that, for a predetermined length of the conduit 300, the linear arrangement allows each conductor to achieve a minimum overall length (i.e., a length substantially equal to the length of the conduit) and, accordingly, the amount of voltage drop on each conductor per unit length of the conduit 300 is minimised, thereby allowing the electrical heater 800 to achieve a maximum circuit length. In the embodiment described above, an electrically insulating layer 6 is provided between the conduit 300 and the fourth conductor 4. The layer 6 is not essential and may be dispensed with, if the tubular wall of the conduit 300 is made of an electrically insulating material, such as, for example, plastics. It will further be appreciated that the arcuate sections 5-4 to 5-6 of the heating elements may be partially or completely omitted since the arcuate sections 5-4 to 5-6 play a limited role in the operation of the electrical heater 800 as described above. That is, the heating element 5 may comprise a plurality of heating element sections (similar to the arcuate sections 5-1 to 5- 3) which are not directly connected to one another. Each heating element section may be disposed between the fourth conductor and a respective one of the first, second and third conductors and may generate heat when an electrical current is passed between the fourth conductor 4 and one of the conductors 1 , 2, 3. Edges of the heating element sections may be aligned to edges of the conductors 1 , 2, 3, such that a separation between adjacent heating element sections around the perimeter of the conduit 300 may be substantially equal to a separation between adjacent ones of the conductors 1 , 2, 3 around the perimeter of the conduit 300.

As illustrated in Figure 2 and described above, each of the conduit 300, the electrically insulating layer 6, the fourth conductor 4 and the heating element 5 is of a tubular shape having a circular cross-sectional shape along a plane normal to the axis V. It will be appreciated that this is not necessary. In practice, one or more of the conduit 300, the electrically insulating layer 6, the fourth conductor 4 and the heating element 5 may have a cross-sectional shape which is generally, but not strictly, circular. The generally circular cross-sectional shape may be due to limitations of manufacturing methods being used to make the conduit 300, the electrically insulating layer 6, the fourth conductor 4 and the heating element 5. In another example, the conduit 300 may have a cross-sectional shape other than a circular shape, such as, rectangular or oval shape, etc. Preferably, each of the electrically insulating layer 6, the fourth conductor 4 and the heating element 5 have a cross- sectional shape similar to that of the conduit 300. However, this is not necessary either.

Further, each of the conductors 1 , 2, 3 is illustrated in Figure 2 as an arc concentric with the conduit 300. It will be appreciated that this is not necessary. A cross-sectional profile of the conductors 1 , 2, 3 may be varied according to a cross-sectional shape of the conduit 300. For example, if the conduit 300 has a rectangular cross-sectional shape, it will be understood that the each of the conductors 1 , 2, 3 may be a flat sheet of material lying on a side surface of the conduit 300, or may be disposed around a corner of the conduit 300 so as to lie partially on two (or more) side surfaces of the conduit 300. It will be appreciated that in practice the central axis V of the conduit 300 (illustrated in Figure 1) may not be a perfectly straight line. Non-straight conduits are often required to transport fluid along a particular path. A non-straight conduit may be manufactured by joining several straight conduit sections together in series with suitable corners, or by deforming a pre- manufactured conduit. It will be understood that in some embodiments, the electrical heater 800 may be applied to a conduit which has previously been formed to a required non-straight path. Alternatively, the electrical heater 800 may be applied to one or more conduit sections prior to assembly. The electrical heater 800 provided with the conduit 300 may have different electrical performance along the length of the conduit 300 so as to provide different levels of heat output to suit the environment where the conduit 300 is located. For example, the width W of the conductors 1 , 2, 3, the gap G between the conductors 1 , 2, 3 or the thickness T of the heating element 5 may vary along the length of the conduit 300.

As illustrated in Figures 2 and 3, the electrical heater 800 is of a substantially tubular shape surrounding the conduit 300. It will be understood that this tubular shape of the electrical heater 800 is mainly determined by the shape of the conduit 300, and is not necessary if the electrical heater 800 is used to heat an object other than a conduit. An example of such an electrical heater is illustrated in Figure 7, in which an electrical heater 800' is provided to heat an object 500. Components of this example that correspond to those of the embodiment described above are labelled using the same numerals as the embodiment but with a prime symbol ' for differentiation. As shown in Figure 7, an electrically insulating layer 6' is provided on a surface 16 of the object 500. The electrical heater 800' is further provided on top of the electrically insulating layer 6'. The electrical heater 800' has a substantially planar profile, where a fourth conductor 4' is disposed on top of the electrically insulating layer 6', and a heating element 5' is disposed on a top surface of the fourth conductor 4', with conductors 1 ', 2', 3' further provided on top of the heating element 5' in a spaced-apart manner.

Figure 7 is a cross-sectional view of the electrical heater 800' and the object 500. The object 500 has a length and extends along a direction generally perpendicular to the cross-sectional plane of Figure 7. The electrical heater 800' is elongated and has a length which extends along a length of the object 500. For example, the electrical heater 800' may be straight and extend in a direction parallel to the length of the object 500. Alternatively, the electrical heater 800' may be wound around the object 500 helically, such that the length of the electrical heater 800' extends generally along the length of the object 500. That is, a central axis of the electrical heater 800' extends along the length of the object 500, but each section of the electrical heater 800' does not strictly extend along the length of the object 500. The overall length of the electrical heater 800' (along the central axis of the electrical heater 800') may not be exactly the same as the length of the object 500. Similarly, each of the conductors , 2', 3', 4' and the heating element 5' is elongated and has a length which extends along a length of the object 500.

The electrically heating element 5' comprises a first surface 17 and a second surface 18 opposite to the first surface 17. The conductors 1', 2', 3' are disposed on the first surface 17. The fourth conductor 4' is disposed on the second surface 18. The conductors 1 ', 2', 3', 4', the heating element 5' and the insulating layer 6' have substantially the same characteristics to the characteristics of their counterparts as described above with reference to Figures 1 to

6, except that each of the conductors 1 ', 2', 3', 4', the heating element 5' and the insulating layer 6' has a flat non-curved profile, which is different from the curved profile of their respective counterpart as shown in Figure 2.

In use, the conductors 1 ', 2', 3' are connected to three output phases of a three-phase power supply (not shown), respectively. The fourth conductor 4' (i.e., the wye point) is generally connected to the earth ground. An electric current which flows out of each of conductors 1', 2', 3' tends to follow an electrical pathway from a respective one of the conductors 1 ', 2', 3', via the electrical heating element 5' and the fourth conductor 4', and back to another one of the conductors 1', 2', 3' via the electrical heating element 5^: again. The resistances of the conductors 1 ', 2', 3', 4' are much smaller than the resistance of the heating element 5'. Therefore, the heating element 5' generates a majority of the heat output by the electrical heater 800'. The heat generated by the heating element 5' is transmitted, through the fourth conductor 4' and the electrically insulating layer 6', to the object 500. The fourth conductor 4' serves as a heat distributor for distributing the heat generated by the heating element 5', thereby allowing the surface 16 of the object 500 to be heated substantially evenly.

From the example described above, it will be appreciated that depending upon the particular shape of an object to be heated, the electrical heater 800' may have any suitable profile which generally follows at least a part of an outer profile of the object, and is not limited to the particular circular profile as shown in Figures 2 and 3 or the planar profile as shown in Figure

7. In particular, as described above, the electrical heater 800' is flexible and therefore can have an outer profile which conforms to at least a part of an outer profile of an object to be heated. It would further be appreciated that regardless of the shape of the electrical heater 800', the electrical heater 800' may be particularly suitable for use as a three-phase electrical heater, and the conductors 1 ', 2', 3' are suitable for connection to a three-phase power supply. The fourth conductor 4' may be connected to the earth ground or may be floating. The conductors 1', 2', 3' are electrically coupled to the fourth conductor 4' via the heating element 5', and therefore the electrical heater 800' are connected in a wye configuration with the fourth conductor 4' being the wye point.

While various embodiments have been described above it will be appreciated that these embodiments are for all purposes exemplary, not limiting. Various modifications can be made to the described embodiments without departing from the scope of the present invention.

Claims

CLAIMS:

1. An electrically heated conduit comprising:

a conduit for conveying fluid, the conduit having a length; and

an electrical heater, the electrical heater comprising:

first, second, and third conductors, wherein each of the first, second, and third conductors extends along the length of the conduit;

a fourth conductor disposed around the conduit and extending along the length of the conduit; and

an electrical heating element disposed between the fourth conductor and the first, second and third conductors, the electrical heating element being arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors.

2. An electrically heated conduit according to claim 1 , wherein the first, second and third conductors are configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the first, second and third conductors are separated from each other of the first, second and third conductors around a perimeter of the conduit.

3. An electrically heated conduit according to claim 2, wherein a separation between adjacent ones of the first, second and third conductors remains substantially constant along the length of the conduit.

4. An electrically heated conduit according to claim 2 or 3, wherein the electrical heating element has a thickness along a radial direction of the conduit, and wherein a separation between adjacent ones of the first, second and third conductors is greater than the thickness of the electrical heating element.

5. An electrically heated conduit according to claim 4, wherein the separation is at least three times the thickness of the electrical heating element.

6. An electrically heated conduit according to any of claims 2 to 5, wherein the first, second and third conductors are evenly spaced apart from each other around the perimeter of the conduit.

7. An electrically heated conduit according to any preceding claim, wherein the first, second and third conductors are configured such that, at a cross-section of the electrical heater along a plane normal to a central axis of the conduit, each of the first, second and third conductors has a respective dimension around a perimeter of the conduit.

8. An electrically heated conduit according to claim 7, wherein the first, second and third conductors have equal dimensions around the perimeter of the conduit.

9. An electrically heated conduit according to claim 7 or 8, wherein a respective dimension of one of the first, second and third conductors around the perimeter of the conduit is at least around three times a separation between adjacent ones of the first, second and third conductors around the perimeter of the conduit.

10. An electrically heated conduit according to any preceding claim, wherein each of the first, second, and third conductors is electrically coupled to the fourth conductor via the electrical heating element.

11. An electrically heated conduit according to any preceding claim, wherein the electrical heating element is disposed around the fourth conductor, and the first, second, and third conductors are further disposed around the electrical heating element.

12. An electrically heated conduit according to any preceding claim, wherein each of the first, second, and third conductors extends along a direction parallel to a central axis of the conduit.

13. An electrically heated conduit according to any preceding claim, wherein the electrical heating element comprises a plurality of heating element sections which are spaced apart from each other.

14. An electrically heated conduit according to any preceding claim, wherein the conduit comprises a tube.

15. An electrically heated conduit according to any preceding claim, wherein one or more of the first, second, third and fourth conductors comprise aluminium or aluminium alloy.

16. An electrically heated conduit according to any preceding claim, wherein the electrical heating element has a positive temperature coefficient of resistance.

17. An electrically heated conduit according to any preceding claim, further comprising an insulating jacket disposed around the electrical heater.

18. An electrically heated conduit according to any preceding claim, wherein the fourth conductor substantially surrounds the conduit.

19. An electrically heated conduit according to any preceding claim, wherein the fourth conductor is of a tubular shape.

20. An electrically heated conduit according to any one of claims 1 to 18, wherein the fourth conductor comprises a plurality of conductor sections which are spaced apart from each other.

21. An electrically heated conduit according to claim 20, wherein the plurality of conductor sections are electrically coupled to the first, second, and third conductors, respectively, via the electrical heating element.

22. A method of installing an electrical heater around a conduit for conveying fluid, the conduit having a length, the method comprising:

providing first, second, and third conductors;

providing a fourth conductor around the conduit; and

providing an electrical heating element,

wherein each of the first, second and third conductors extends along the length of the conduit, and the fourth conductor extends along the length of the conduit, and wherein the electrical heating element is disposed between the fourth conductor and the first, second and third conductors, and is arranged to generate heat when an electrical current is passed between the fourth conductor and one or more of the first, second and third conductors.

23. A method according to claim 22, wherein providing a fourth conductor around the conduit comprises disposing the fourth conductor around the conduit, and disposing the fourth conductor around the conduit further comprises wrapping a layer of electrically conductive material around the conduit to substantially surround the conduit; and wherein the wrapped layer of electrically conductive material forms the fourth conductor.

24. A method according to claim 22 or 23, wherein providing an electrical heating element comprises disposing the electrical heating element around the conduit.

25. A method according to claim 24, wherein disposing the electrical heating element around the conduit comprises wrapping a layer of electrical heating material around the conduit, and wherein the wrapped layer of electrical heating material forms the electrical heating element.

26. A method according to claim 25, wherein the layer of electrical heating material is formed by extrusion.

27. A method according to any of claims 22 to 26, wherein providing first, second, and third conductors comprises spraying electrically conductive material along the length of the conduit, and the sprayed electrically conductive material forms the first, second, and third conductors.

28. An electrical heater, the electrical heater being elongated and having a length, the heater being configurable, in use, such that the length of the heater extends along a length of an object to be heated, the electrical heater comprising:

first, second, and third conductors for connecting to a three-phase power supply; a fourth conductor; and

29. An electrical heater according to claim 28, wherein the electrical heater is for use with a conduit for conveying fluid, the conduit having a length.

30. An electrical heater according to claim 29, wherein each of the first, second, and third conductors is configurable, in use, to extend along the length of the conduit.

31. An electrical heater according to claim 29 or 30, wherein the fourth conductor is configurable, in use, to be disposed around the conduit and to extend along the length of the conduit such that the fourth conductor substantially surrounds the conduit.