Cartridge heating element for a medium-voltage heater
The cartridge heater design uses separate core and sheath insulations of ceramic and boron nitride materials to address high material costs and ensure reliable operation with optimized insulation and thermal management, achieving cost-effective manufacturing and safety.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SCHNIEWINDT
- Filing Date
- 2025-12-12
- Publication Date
- 2026-06-18
Smart Images
Figure EP2025086822_18062026_PF_FP_ABST
Abstract
Description
[0001] Schniewindt GmbH & Co. KG December 12, 2025
[0002] 124178 WO
[0003] 1
[0004] Cartridge heating element for a medium-voltage heater
[0005] The invention relates to a cartridge heater for a medium-voltage heater, comprising a heating conductor which runs in a concentric helix radially spaced from a longitudinal center axis of the cartridge heater in the longitudinal direction of the cartridge heater, a centered return conductor which runs in the longitudinal center axis of the cartridge heater, and a sheathing tube which surrounds the return conductor and the heating conductor at a predetermined radial distance to the heating conductor.
[0006] For a medium-voltage heater, several such cartridge heaters are connected in series, with a voltage drop of approximately [value] across each cartridge heater.
[0007] A voltage of 1 kV occurs. To achieve an operating voltage of 4 kV to 20 kV for the medium-voltage heater, a corresponding number of cartridge heaters must be connected in series. The insulation of each cartridge heater isolates the entire operating voltage of the medium-voltage heater, thus ensuring reliable and safe operation of the medium-voltage heater in the long term.
[0008] The invention is based on the objective of providing a cartridge heating element for a medium-voltage heater that can be manufactured with less expenditure on the materials required for its production, while ensuring equally reliable and safe long-term operation of the medium-voltage heater.
[0009] This problem is solved according to the invention by the cartridge heater having a core insulation arranged between the return conductor centered in the cartridge heater and the heating conductor surrounding the return conductor, and a sheath insulation arranged between the heating conductor and the sheath tube of the cartridge heater. By dividing the insulation of the cartridge heater into the core insulation and the separate sheath insulation, the technical possibility arises of providing the necessary insulation between the centered return conductor and the heating conductor concentrically surrounding it.
[0010] Core insulation for the voltage drop occurring at the cartridge heating element, from Schniewindt GmbH & Co. KG, December 12, 2025
[0011] 124178 WO
[0012] 2. The core insulation is designed to withstand the operating voltage of the medium-voltage heater, whereas the sheath insulation between the heating element and the outer casing is designed to meet the requirements of the medium-voltage heater. Due to the different requirements for the core insulation material and the sheath insulation material, this results in a cartridge heater that can be manufactured with significantly lower economic costs compared to the prior art.
[0013] The core insulation of the cartridge heater can be advantageously designed to withstand a voltage drop of, for example, 1 kV across the cartridge heater.
[0014] Accordingly, according to an advantageous further development of the cartridge heater according to the invention, its jacket insulation can be designed for the operating voltage of a medium-voltage heater comprising a plurality of such cartridge heaters, e.g. for 4 kV to 20 kV.
[0015] According to a particularly advantageous embodiment of the cartridge heater according to the invention, its core insulation is made of a ceramic material, e.g., magnesium oxide. Such ceramic materials, especially magnesium oxide, possess a high coefficient of thermal expansion and high dielectric strength, as required, thereby ensuring permanent electrical insulation between the centered return conductor and the heating conductor of the cartridge heater, while the economic cost of providing these materials is comparatively low.
[0016] Advantageously, the outer insulation of the cartridge heater can be made of boron nitride, allowing for a requirements-compliant design of the outer insulation with comparatively low economic costs. The relatively low coefficient of thermal expansion of boron nitride can be compensated for by the comparatively high coefficient of thermal expansion of the ceramic material forming the core insulation, as mentioned above.
[0017] In an advantageous embodiment of the cartridge heater according to the invention, Schniewindt GmbH & Co. KG, December 12, 2025
[0018] 124178 WO
[0019] 3 is a comparatively high coefficient of thermal expansion, which results in a high dielectric strength, e.g. 10 kV / mm, of core insulation of approx. 11x10'. 6 K' 1sufficient to achieve a comparatively low coefficient of thermal expansion of approximately 1.5 x 10' for the boron nitride-based jacket insulation. 6 K' 1 to compensate.
[0020] A permanently correct and fixed arrangement of the heating conductor within the cartridge heater according to the invention is achieved with minimal technical and structural effort if the heating conductor of the cartridge heater sits on its core insulation.
[0021] If a round adapter is arranged at the end section of the core insulation of the cartridge heater according to the invention furthest from the connection, and this adapter is located between the axial end surface of the core insulation and a base surface of the outer insulation spaced axially from it, and by means of which the heating conductor is kept at a constant distance from the outer tube, optimal heat dissipation can be ensured. This prevents a local increase in thermal stress, which would otherwise result from the heating conductor being routed towards the core of the cartridge heater, and thus a point of failure.
[0022] According to an advantageous further development of the cartridge heating element according to the invention, its round adapter has an axial through-hole in which the centered return conductor sits and is soldered or welded to the round adapter.
[0023] Accordingly, the round adapter of the cartridge heater according to the invention advantageously has a radial bore in which the heating conductor sits and is soldered or welded to the round adapter. This prevents the heating conductor wire from burning out during soldering due to the large mass differences between the heating conductor wire on the one hand and the round adapter on the other.
[0024] Advantageously, in the cartridge heating element according to the invention, silver solder is used as the soldering medium between the round adapter on the one hand and the return conductor or the heating conductor on the other. Schniewindt GmbH & Co. KG, December 12, 2025
[0025] 124178 WO
[0026] 4
[0027] If a thermocouple is embedded in the core insulation of the cartridge heater according to the invention, the operation of the cartridge heater can be thermally monitored and, in particular, the core temperature of the cartridge heater can be evaluated.
[0028] According to an advantageous embodiment of the cartridge heater according to the invention, the thermocouple embedded in the core insulation is connected to the centered return conductor.
[0029] For this purpose, the thermocouple is expediently arranged in an extension of an axial through-hole in the core insulation that accommodates the centered return conductor.
[0030] In an advantageous further development of the cartridge heater according to the invention, the thermocouple is welded at its free tip in the core insulation and is preferably fixed in the core insulation by means of ferrous cement.
[0031] Furthermore, in the cartridge heating element according to the invention, a sealing plug is expediently arranged at its connection-side end section, through which a connecting wire of the heating conductor, a connecting section of the centered return conductor and a connecting line of the thermocouple run.
[0032] In an inventive method for manufacturing a cartridge heater, a core insulation with an axial through-hole is produced from a ceramic material, the core insulation is pushed onto a centered return conductor that can be received in the axial through-hole, a helical heating conductor is pulled onto the outer surface of the core insulation and fixed there, boron nitride molded parts forming a sheath insulation are inserted into a sheath tube of the cartridge heater, creating an inner cavity, the core insulation, which has the centered return conductor in its axial through-hole and the heating conductor fixed on its outer surface, is inserted into the inner cavity of the sheath insulation, the connections of the cartridge heater are threaded through a sealing plug, and the sealing plug is inserted into the connection end of the cartridge heater. Schniewindt GmbH & Co. KG, December 12, 2025
[0033] 124178 WO
[0034] 5
[0035] The outer casing is pressed in and the diameter of the cartridge heating element is reduced in a rotary kneading machine.
[0036] Advantageously, the axial through-hole of the core insulation is enlarged, preferably by means of a wire saw, and a thermocouple with a connecting cable is inserted into the enlarged axial through-hole thus created, welded at its free tip and fixed by means of ferrous cement.
[0037] According to a further advantageous embodiment of the method according to the invention, a round adapter is arranged on the end section of the core insulation furthest from the connection, to which the centered return conductor and the heating conductor are soldered or welded, preferably using silver solder, and which is received between the axial end surface of the core insulation and a base surface of the sheath insulation when the core insulation is inserted into the sheath insulation.
[0038] The invention will now be explained in more detail with reference to one embodiment and the drawing. The drawing shows:
[0039] Figure 1 shows a schematic representation of a longitudinal section through an embodiment of a cartridge heating element according to the invention for a medium-voltage heater; and
[0040] Figure 2 shows a schematic representation of a cross-section through the embodiment of the cartridge heater according to the invention shown in Figure 1.
[0041] A cartridge heater 1, described below with reference to an embodiment, serves as a heating element for a medium-voltage heater (not shown in Figures 1 and 2). For such a medium-voltage heater, several of these cartridge heaters 1, e.g., 4 to 25 cartridge heaters 1, are connected in series. During operation of the medium-voltage heater, a voltage drop of approximately 1 kV occurs across each of the cartridge heaters 1 connected in series. To achieve an operating voltage of 4 kV to 20 kV for the medium-voltage heater, a corresponding number of cartridge heaters 1 must be connected.
[0042] The cartridge heater 1 has a heating conductor 2 and a longitudinal central axis. Schniewindt GmbH & Co. KG, December 12, 2025
[0043] 124178 WO
[0044] 6
[0045] The heating conductor 2 extends in a helical line concentric to the longitudinal axis 3 of the cartridge heater 1 in the longitudinal direction of the cartridge heater 1.
[0046] Between the longitudinal center axis 3 or the centered return conductor running therein
[0047] A radial distance exists between the return conductor 4 on the one hand and the heating conductor 2, which runs in the aforementioned helical path, on the other. The arrangement formed by the centered return conductor 4 and the heating conductor 2 is housed within a sheathing tube 5 of the cartridge heater 1, with a radial distance also existing between the inner sheathing surface of the sheathing tube 5 and the heating conductor 2, which runs in the helical path.
[0048] The cartridge heater 1 has a core insulation 6, which is arranged between the centered return conductor 4 running along the longitudinal axis 3 of the cartridge heater 1 and the heating conductor 2 surrounding this return conductor 4 in the aforementioned helical path, with the heating conductor 2 essentially sitting on the outer surface of the core insulation 6. The core insulation 6 is designed to withstand the voltage drop occurring across the individual cartridge heater 1, which, in the case of the described embodiment of the cartridge heater 1, is approximately 1 kV, as mentioned above. This core insulation 6 can be made of a suitable ceramic material, e.g., magnesium oxide. Accordingly, the core insulation 6 can exhibit a comparatively high coefficient of thermal expansion of approximately 1.5 x 10⁻⁶ 6 K' 1 and have a high dielectric strength, e.g. of 10 kV / mm.
[0049] In addition to the core insulation 6, the cartridge heater 1 has a jacket insulation 7, which is arranged between the helical heating conductor 2 on the one hand and the inner surface of the jacket tube 5 of the cartridge heater 1 on the other. The jacket insulation 7 is designed for the full operating voltage of the medium-voltage heater comprising multiple cartridge heaters 1, e.g., for 4 kV to 20 kV. In the case of the embodiment of the cartridge heater 1 described here, this jacket insulation is made of boron nitride. Accordingly, the jacket insulation 7 has a comparatively low coefficient of thermal expansion, which is approximately 1.5 x 10⁻⁶ 6 K' 1 can amount to. In the operation of the cartridge heater 1 or the medium-voltage heater comprising a plurality of such cartridge heaters 1, the comparatively high coefficient of thermal expansion is Schniewindt GmbH & Co. KG December 12, 2025
[0050] 124178 WO
[0051] The magnesium oxide core insulation 6 of the cartridge heater 1 is sufficient to compensate for the comparatively low coefficient of thermal expansion of the boron nitride sheath insulation 7 of the cartridge heater 1. The core insulation 6 thus serves to compensate for the comparatively low coefficient of thermal expansion of the boron nitride sheath insulation 7 and to ensure electrical insulation between the helical heating conductor 2 on the one hand and the centered return conductor 4 on the other.
[0052] Instead of magnesium oxide, other ceramic materials can also be used as material for the core insulation 6, whereby a high coefficient of thermal expansion, high dielectric strength and the lowest possible material costs are the focus when selecting a suitable material.
[0053] The outer casing 5 and the outer casing insulation 7 are closed at the left end of the cartridge heater 1 in Figure 1. A round adapter 8 is arranged between the base surface of the outer casing insulation 7 and the axial end surface of the core insulation 6 opposite this base surface. The thickness of the round adapter 8 corresponds to the axial distance between the base surface of the outer casing insulation and the axial end surface of the core insulation 6 opposite it. This round adapter 8 holds the helical heating element 2 at a constant distance from the outer casing 5 at the closed end section of the cartridge heater 1. This ensures optimal heat dissipation.In contrast, an offset or relocation of the helical heating conductor 2 towards the longitudinal central axis 3 of the cartridge heater 1 would lead to a local increase in thermal stress, which would result in an unwanted and therefore avoidable predetermined breaking point of the cartridge heater 1.
[0054] The round adapter 8 has an axial through-hole. The end section of the centered return conductor 4, facing the round adapter 8, sits in this axial through-hole. This end section is, for example, soldered to the round adapter 8 using silver solder or welded to the round adapter 8.
[0055] Furthermore, the round adapter 8 has a radial bore in which the end section of the heating conductor 2 facing the round adapter 8 is seated. This end section Schniewindt GmbH & Co. KG December 12, 2025
[0056] 124178 WO
[0057] The heating conductor 2 is also soldered or welded to the round adapter 8, for example, using silver solder. The radial bore of the round adapter 8 prevents the heating conductor 2 from burning out due to the large mass difference between the round adapter 8 and the heating conductor wire.
[0058] In the embodiment of the cartridge heater 1 shown in Figures 1 and 2, it is equipped with a thermocouple 9. The core temperature of the cartridge heater 1 can be measured and thus evaluated using this thermocouple 9. For this purpose, the thermocouple 9 is embedded in the core insulation 6 in such a way that it is in contact with the centered return conductor 4. To ensure this, an axial through-hole 10 in the core insulation 6, in which the centered return conductor 4 of the cartridge heater 1 is received, is provided with an extension. The thermocouple 9 is received in this extension of the axial through-hole 10 and, as can best be seen in Figure 2, is in contact with the centered return conductor 4. At its free tip, the thermocouple 9 is welded to the core insulation and fixed there with ferrous cement. The thermocouple 9 is led out of the cartridge heater 1 along the centered return conductor 4.
[0059] At its terminal end, opposite the closed end section, the cartridge heating element 1 has a sealing plug. A connecting wire 11 of the heating conductor 2, a connecting section 12 of the centered return conductor 4, and a connecting lead 13 of the thermocouple 9 run through this sealing plug.
[0060] To manufacture the cartridge heating element 1 described above, the heating conductor 2 is wound onto a mandrel to give it its helical shape. If the magnesium oxide core insulation 6 has a diameter of 18.4 mm, the mandrel can have a diameter of 16 mm, since the helical shape of the heating conductor 2 widens slightly after winding. The connecting strand 11 of the heating conductor 2 consists of one core of the heating conductor 2 wrapped with three cores of CuNi44 wire with a diameter of 0.7 mm. The core insulation 6 is manufactured with the axial through-hole 10, or the axial through-hole 10 is cut into the core insulation 6. The axial through-hole 10 is enlarged using a wire saw. Then the [unclear - possibly referring to a specific product or process] is [unclear - possibly referring to a specific product or process]. Schniewindt GmbH & Co. KG, December 12, 2025
[0061] 124178 WO
[0062] The core insulation 6, provided with an axial through-hole 10, is pushed onto the centered return conductor 4, with the centered return conductor 4 being received in the axial through-hole 10. The thermocouple 9 with its connecting lead 13 is inserted into the previously created enlargement of the axial through-hole 10, welded at its free tip, and fixed with ferrous cement.
[0063] The helical heating conductor 2 is then pulled onto the outer surface of the core insulation 6 and subsequently fixed there.
[0064] Boron nitride components are inserted into the jacket tube s of the cartridge heater 1, by means of which the jacket insulation 7 is formed by creating an inner cavity.
[0065] Then, the round adapter 8 is positioned at the end section furthest from the connection of the core insulation 6, which is provided with the helical heating conductor 2 fixed to its outer sheath surface and in whose axial through-hole 10 the centered return conductor 4 is located. The end section of the centered return conductor 4 is welded or soldered with silver solder into the axial through-hole of the round adapter 8, and the end section of the heating conductor 2 is welded or soldered with silver solder into the radial bore of the round adapter 8. The core insulation 6, fitted with the round adapter 8, is inserted into the inner cavity of the sheath insulation 7 located in the sheath tube 5 until the round adapter 8 comes into contact with the base surface of the sheath insulation 7.
[0066] The connecting wire 11 of the heating conductor 2, the connecting section 12 of the centered return conductor 4, and the connecting lead 13 of the thermocouple 9 are threaded through a sealing plug, which can be manufactured using a 3D printing process. The sealing plug is pressed into the outer casing 5 of the cartridge heater 1 to seal the cartridge heater 1. In a subsequent process step, the diameter of the sealed cartridge heater 1 is reduced in a rotary kneading machine, thereby compacting the interior of the cartridge heater 1.
Claims
Schniewindt GmbH & Co. KG December 12, 2025 124178 WO 10 Patent claims 1. Cartridge heater for a medium-voltage heater, comprising a heating conductor (2) extending in a concentric helix radially spaced from a longitudinal center axis (3) of the cartridge heater (1), a centered return conductor (4) extending in the longitudinal center axis (3) of the cartridge heater (1), and a sheath tube (5) surrounding the return conductor (4) and the heating conductor (2) at a predetermined radial distance from the heating conductor (2), characterized in that the cartridge heater (1) has a core insulation (6) arranged between the return conductor (4) centered in the cartridge heater (1) and the heating conductor (2) surrounding the return conductor (4), and a sheath insulation (7) arranged between the heating conductor (2) and the sheath tube (5) of the cartridge heater (1).
2. Cartridge heater according to claim 1, the core insulation (6) of which is designed for the voltage drop of the cartridge heater (1), e.g. for 1 kV.
3. Cartridge heater according to claim 1 or 2, the jacket insulation (7) of which is designed for the operating voltage of a medium-voltage heater comprising a plurality of cartridge heaters (1), e.g. for 4 kV to 20 kV.
4. Cartridge heater according to one of claims 1 to 3, the core insulation (6) of which is made of a ceramic material, e.g. magnesium oxide.
5. Cartridge heater according to one of claims 1 to 4, the jacket insulation of which is made of boron nitride.
6. Cartridge heater according to claim 5, wherein the core insulation (6) of approximately 11x10' has a comparatively high coefficient of thermal expansion and a high dielectric strength, e.g. 10 kV / mm. 6 K' 1is sufficient to achieve a comparatively low coefficient of thermal expansion of the boron nitride-based sheath insulation (7) of approximately 1.5 x 10' 6 K' 1 to compensate.
7. Cartridge heating element according to one of claims 1 to 6, wherein the heating conductor (2) Schniewindt GmbH & Co. KG December 12, 2025 124178 WO 11 sits on the core insulation (6).
8. Cartridge heater according to one of claims 1 to 7, in which a round adapter (8) is arranged at the end section of the core insulation (6) furthest from the connection, which is located between the axial end surface of the core insulation (6) and a base surface of the jacket insulation (7) spaced apart from it in the axial direction of the cartridge heater (1), and by means of which the heating conductor (2) can be held at a constant distance to the jacket tube (5).
9. Cartridge heating element according to claim 8, wherein the round adapter (8) has an axial through-hole in which the centered return conductor (4) is seated and is soldered or welded to the round adapter (8).
10. Cartridge heating element according to claim 8 or 9, wherein the round adapter (8) has a radial bore in which the heating conductor (2) is seated and connected to the round adapter (8) is soldered or welded.
11. Cartridge heating element according to claim 9 or 10, wherein the soldering medium between the round adapter (8) on the one hand and the return conductor (4) or the heating conductor (2) on the other hand is silver solder.
12. Cartridge heater according to one of claims 1 to 11, wherein a thermocouple (9) is embedded in the core insulation (6).
13. Cartridge heater according to claim 12, wherein the thermocouple (9) embedded in the core insulation (6) is in contact with the centered return conductor (4).
14. Cartridge heating element according to claim 12 or 13, wherein the thermocouple (9) is arranged in an extension of an axial through-hole (10) of the core insulation (6) that accommodates the centered return conductor (4).
15. Cartridge heating element according to one of claims 12 to 14, wherein the thermocouple (9) is welded at its free tip in the core insulation (6) and is fixed in the core insulation, preferably by means of ferrous cement. Schniewindt GmbH & Co. KG December 12, 2025 124178 WO 12 16. Cartridge heating element according to one of claims 12 to 15, at the connection-side end section of which a sealing plug is arranged, through which a connecting wire (11) of the heating conductor (2), a connecting section (12) of the centered return conductor (4) and a connecting line (13) of the thermocouple (9) run.
17. Method for manufacturing a cartridge heater (1) in which a core insulation (6) with an axial through-hole (10) is made of a ceramic material, in which the core insulation (6) is pushed onto a centered return conductor (4) that can be received in the axial through-hole (10), in which a helical heating conductor (2) is pulled onto the outer sheath surface of the core insulation (6) and fixed there, in which boron nitride molded parts forming a sheath insulation (7) are inserted into a sheath tube (5) of the cartridge heater (1) forming an inner cavity, in which the core insulation (6), which has the centered return conductor (4) in its axial through-hole (10) and the heating conductor (2) fixed thereon on its outer sheath surface, is inserted into the inner cavity of the sheath insulation (7), in which the connections (11, 12) of the cartridge heater (1) are connected by a The sealing plugs are threaded on,in which the sealing plug at the connection end of the cartridge heating element (1) is pressed into its jacket tube (5) and in which the diameter of the cartridge heating element (1) is reduced in a rotary kneading machine.
18. Method according to claim 17, wherein the axial through-hole (10) of the core insulation (6) is enlarged, preferably by means of a wire saw, and a thermocouple (9) with a connecting lead (13) is inserted into the enlargement of the axial through-hole (10) thus created, welded at its free tip and fixed by means of ferrous cement.
19. Method according to claim 17 or 18, wherein a round adapter (8) is arranged on the end section of the core insulation (6) furthest from the connection, to which the centered return conductor (4) and the heating conductor (2) are soldered or welded, preferably by means of silver solder, and which is received between the axial end surface of the core insulation (6) and a base surface of the sheath insulation when the core insulation (6) is inserted into the sheath insulation (7).