TRANSFORMER

Abstract: Transformer having a coil carrier (1) which comprises a coil tube (2) with a first flange (3) and a second flange (4), a primary coil (21) and a secondary coil (22) between the first and the second flange, high voltage contacts (6), low voltage contacts (5), a magnetic flux conductor (25) in, laterally of, and transverse to the coil tube (2), in which a first part (8) of the magnetic flux conductor (25) which extends transversely to the coil tube (2) is enclosed in a trough-shaped holder (9) with ends, which holder (9) is integral with the first flange, and in which the low voltage contacts (5) extend transversely to the coil tube (2) and to the holder (9). The first flange (3) extends at a side of the coil tube (2) where the low voltage contacts (5) are located to farther away from the coil tube (2) alongside the low voltage contacts than at a side opposed thereto. A separation is thus created between the magnetic flux conductor (25) and the low voltage contacts (5) of the transformer, whereby a comparatively long creepage path and a comparatively long clearance distance are realized between the high voltage side and the low voltage side of the transformer. In a situation where a sudden high mains voltage arises, this will prevent the high voltage from reaching the low voltage contacts (5) through the magnetic flux conductor (25).

Description: Transformer. The invention relates to a transformer which comprises: a coil carrier with a hollow coil tube which has a first flange and a second flange; a primary coil and a secondary coil around the coil tube between the first flange and the second flange; high-voltage contacts at the second flange in connection with the primary coil; low-voltage contacts at the first flange in connection with the secondary coil; a magnetic flux conductor in, laterally of, and transverse to the coil tube; a first portion of the magnetic flux conductor which extends transversely to the coil tube being accommodated in a trough-shaped holder with ends, which holder is integral with the first flange; and the low-voltage contacts extending transversely to the coil tube and transversely to the trough-shaped holder. Such a transformer is known from WO 97/05632. In the known transformer, a magnetic flux conductor is formed by an E-shaped core which is present inside and laterally of a coil tube and which cooperates with an I-shaped core which extends transversely to the coil tube and is present in a trough-shaped holder. A comparatively thick insulation layer around the primary or around the secondary coil is necessary for obtaining a safeguard against electrical breakdown between the primary and the secondary coil in accordance with a generally accepted safety standard. It is usual in these transformers to provide this comparatively thick insulation layer around the secondary coil, which is present at the low-voltage side. The secondary coil in this case consists of, for example, triple-insulated wire. This secondary coil has fewer turns than does the primary coil, so that the cost of this insulation layer can remain limited. The primary coil in this situation has a comparatively low insulation value, so that a breakdown will occur between the primary coil and the cores if an overvoltage should arise on the high- voltage contacts at the high- voltage side of the transformer. These cores, accordingly, form part of the high-voltage side in the case of any breakdown. A disadvantage of the known transformer is that the high- voltage side is not securely separated from the low-voltage side. A breakdown from the primary coil to the cores involves the risk of breakdown from the high- voltage side to the low- voltage side because the low-voltage contacts, which belong to the low-voltage side, are present adjacent the cores, which belong to the high-voltage side. When these transformers are used in a circuit, therefore, the safety of operators handling this circuit with transformer is not guaranteed. In addition, there is a risk of damage to further electrical components in the circuit which are in connection with the low-voltage contacts because high- voltage is capable of reaching the low- voltage side of the transformer. It is an object of the invention to provide a transformer of the kind mentioned in the opening paragraph in which the high-voltage side is separated with a high degree of security from the low-voltage side. According to the invention, the above object is achieved by the transformer which is characterized in that the first flange extends along the low-voltage contacts to farther from the coil tube at a side of the coil tube where the low-voltage contacts are present than at a side of the coil tube opposed thereto. The first flange thus forms an additional electrical separation between the magnetic flux conductor and the low-voltage contacts. On the one hand, the first flange constitutes a comparatively long distance for arcing through the air, the so-called clearance distance, between the magnetic flux conductor and the low-voltage contacts, and on the other hand a comparatively long creepage path between the magnetic flux conductor and the low-voltage contacts is formed. The creepage path is the shortest path along which a current, a so-called creepage current, can flow along material which is present between the magnetic flux conductor and the low- voltage contacts. The creepage current flows along the surface of the material as a result of, for example, pollutants and moisture present on the material and is dependent on the type of synthetic resin of which the material consists. Since the first flange forms a comparatively long clearance distance, no arcing through the air can take place between the magnetic flux conductor and the low- voltage contacts, given usual values of overvoltages. In addition, the lengthened flange forms a comparatively long creepage path from the magnetic flux conductor along the surface of one side of the flange, over the edge and along the surface of the other side of the flange, along the surface of the holder to the low- voltage contacts of the transformer. It is favorable, furthermore, when a wall transverse to the first flange is present at each end of the trough-shaped holder and also at the first flange, which wall extends along the low- voltage contacts. This renders it possible for the low-voltage contacts to be present close to the ends without a comparatively short creepage path from the low-voltage contacts to the magnetic flux conductor being caused thereby. It is furthermore favorable for this purpose when the wall, seen transversely to the first flange, extends to beyond the trough-shaped holder. An embodiment of the transformer according to the invention is characterized in that the coil tube has a rectangular cross-section with an opening at each of two mutually opposed sides. A better thermal contact between the coils wound around the coil tube and a portion of the magnetic flux conductor present in the coil tube is obtained through the openings. This is favorable for the removal of heat generated in the coils to the portion of the magnetic flux conductor present in the coil tube. The transformer according to the invention will be explained in more detail below with reference to the drawings, in which Fig. 1 shows a first embodiment of the transformer according to the invention in side elevation, partly broken away, Fig. 2 shows the transformer of Fig. 1 in a perspective view along II, Fig. 3 shows the transformer of Fig. 2 in exploded view, Fig. 4 shows a second embodiment of the transformer according to the invention in exploded view, and Fig. 5 is a cross-section taken on the line V-V in Fig. 4. The transformer according to the invention shown in Fig. 1 and Fig. 2 comprises a coil carrier 1 which has a hollow coil tube 2 with a first flange 3 and a second flange 4. As is visible in Fig. 1, a primary coil 21 and a secondary coil 22 are present around the coil tube 2. In the Figure, a portion of the secondary coil 22 has been left out so as to show the primary coil 21 which is situated below the secondary coil 22. The primary and secondary coils 21 and 22 have been left out in Figs. 2, 3, 4 and 5 so as to render the coil tube 2 visible. Low- voltage contacts 5 are present adjacent the first flange 3, and high-voltage contacts 6 are present adjacent the second flange 4. In this embodiment as shown in Figs. 2 and 3, a magnetic flux conductor 25 formed by an E-shaped core 7 is present in and laterally of the coil tube 2, cooperating with an I-shaped core 8 which is present transverse to the coil tube 2 in a trough- shaped holder 9 with open ends 10, which holder 9 is integral with the first flange 3. The low- voltage contacts 5 extend transversely to the coil tube 2 and transversely to the I-shaped core 8 and are formed by pins in this embodiment. As is visible in Figs. 2 and 3, the first flange 3 extends at a side of the coil tube 2 where the low-voltage contacts 5 are present, along the low- voltage contacts 5 to farther away from the coil tube 2 than at an opposite side of the coil tube 2. This is indicated in Fig. 2 as the distance a on the first flange 3 at the side of the coil tube 2, where the low-voltage contacts 5 are present, which distance is greater than a distance b at the opposite side of the coil tube 2. The first flange 3 in this manner forms an additional electrical separation between the cooperating cores 7 and 8 and the low- voltage contacts 5. The separation creates a comparatively long creepage path, indicated with an arrow in broken lines in Fig. 1 and extending from the cooperating cores 7 and 8 along the surface at one side of the flange, over the edge and along the surface at the other side of the flange 3, along the surface of the holder 9 to the low- voltage contacts 5 of the transformer. Furthermore, a comparatively long creepage path is also realized in this manner from a fastening point 30 of the secondary coil 27 to the low- voltage contacts 5, where the triple insulation is usually subject to degradation, to the primary coil at the high- voltage side, which benefits the high-security separation between the high-voltage side and the low-voltage side. It is further apparent in Figs. 2 and 3 that a wall 11 transverse to the first flange 3 is present at each end of the trough- shaped holder 9 and also at the first flange 3, which wall extends along the low-voltage contacts 5, which is indicated as a distance c in Fig. 2. In addition, the wall 11 extends, seen transversely to the first flange 3, to beyond the trough-shaped holder 9, which is indicated as a distance d in Fig. 2. Further additional electrical separations have thus been created between the cooperating cores 7 and 8 on the one hand and the low-voltage contacts 5 on the other hand, so that the low-voltage contacts 5 may be present close to the ends without a comparatively short creepage path from the low-voltage contacts 5 to the magnetic flux conductor 25 being caused thereby. It is noted that this invention offers a possibility of separating the high- voltage side with high security from the low-voltage side also in miniaturized transformers, such as switch mode transformers. It is also noted that the lengthened flange offers an additional protection against damage to the magnetic flux conductor if the transformer should inadvertently be dropped. Figs. 4 and 5 show a second embodiment of the transformer according to the invention in which the coil tube 2 has a rectangular cross-section with an opening 12 at each of two mutually opposed sides. The second embodiment of the transformer according to the invention further comprises substantially the same components as the first embodiment. Corresponding components of the first and second embodiments have been given the same reference numerals in Figs. 4 and 5. A better thermal contact between the coils 21 and 22 wound around the coil tube 2 visible in Fig. 1 on the one hand and the portion of the magnetic flux conductor 25 present inside the coil tube, a portion of the E-shaped core 7 in this embodiment, on the other hand is achieved through the openings 12. This is favorable for the removal of heat generated in the coils 21 and 22 to the E-shaped core 7. The transformer will remain comparatively cool owing to the comparatively large cooling surface area of the core 7, which benefits the power capacity of the transformer.

Claims: CLAIMS: 1. A transformer which comprises: a coil carrier (1) with a hollow coil tube (2) which has a first flange (3) and a second flange (4); a primary coil (21) and a secondary coil (22) around the coil tube (2) between the first flange (3) and the second flange (4); high- voltage contacts (6) at the second flange (4) in connection with the primary coil (21); low-voltage contacts (5) at the first flange (3) in connection with the secondary coil (22); - a magnetic flux conductor (25) in, laterally of, and transverse to the coil tube (2); a first portion (8) of the magnetic flux conductor (25) which extends transversely to the coil tube (2) being accommodated in a trough-shaped holder (9) with ends (10), which holder (9) is integral with the first flange (3); and - the low- voltage contacts (5) extending transversely to the coil tube (2) and transversely to the trough-shaped holder (9). characterized in that the first flange (3) extends along the low- voltage contacts (5) to farther from the coil tube (2) at a side of the coil tube (2) where the low- voltage contacts (5) are present than at a side of the coil tube (2) opposed thereto. 2. A transformer as claimed in claim 1, characterized in that a wall (11) transverse to the first flange (3) is present at each end (10) of the trough-shaped holder (9) and also at the first flange (3), which wall (11) extends along the low- voltage contacts (5). 3. A transformer as claimed in claim 2, characterized in that the wall (11), seen transversely to the first flange (3), extends to beyond the trough-shaped holder (9). 4. A transformer as claimed in claim 1, characterized in that the coil tube (2) has a rectangular cross-section with an opening (12) at each of two mutually opposed sides.

Inventors: CLAUS PATRICK A F, VAN GESTEL PATRICK H, CLAUS, PATRICK, A., F., VAN GESTEL, PATRICK, H.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H01F27
IPC codes: H01F27, H01F30