T 0074/02 02-06-2004

Summary of Facts and Submissions

I. The proprietor of the patent filed an appeal against the decision of the opposition division revoking European patent No. 0 731 994.

II. The following documents of the state of the art have played a role in the appeal:

E3: DE-A-3 211 119;

E5: DE-U1-8 502 491;

F2: Prospectus from the firm Euromold, carrying a date of March 1990, part 7.2 "Zubehör der Serie 600 für 800A"; and

F3: DIN standard 47636, parts 1, 2 and 3 carrying a date of January 1986 and part 5 carrying a date of October 1989.

III. Oral proceedings before the board took place on 2 June 2004.

During the oral proceedings, the appellant (patentee) filed new claims 1 to 11 and new columns 1 and 2 of the description. He requested that the decision under appeal be set aside and that the patent be maintained in amended form on the basis of claims 1 to 11 filed during the oral proceedings.

The respondent (opponent) requested that the appeal be dismissed.

IV. Claims 1 and 2 of the patent in suit as amended read as follows:

"1. Device for interconnecting a high voltage cable with an apparatus or with a second high voltage cable, comprising

- a cable termination (30) which consists of an elastomeric body (36) with a stress relief device (34) and a connector shield (35) integrated therein, the body (36) having a conical interface surface (37) and an outer conductive screen (39); and

- a rigid insulator (41) having a conical interface surface (42) complementary to the interface surface (37) of the cable termination (30);

wherein the angle alpha defining the conical surface (42) of the rigid insulator (41) is between 15° and 45°."

"2. Device for interconnecting high voltage apparatus, comprising

- two rigid insulators (81, 82) each having a conical interface surface (83, 84) and being fastened to respective apparatus (79, 80) to be interconnected; and

- an elastomeric body (90) with a connector shield integrated therein and with an outer conductive screen (91);

wherein the body (90) has two conical interface surfaces (85, 86) complementary to the conical interface surfaces (83, 84) of the rigid insulators (81, 82) with the angle alpha defining the conical surfaces of the rigid insulators (41, 81, 82, 93) being between 15° and 45°."

Claims 3 to 11 are dependent on claim 1 or 2.

V. The arguments of the appellant can be summarised as follows:

Document F3 was a standard concerning apparatus connection parts with external cones, for voltages of 24. kV and 36 kV. In particular, the Figures 1 of parts 1, 2, 3 and 5 of document F3 each showed an apparatus wall, a cable connection part outside of the apparatus in the upper portion of the figure, and an insulating cone in the lower portion of the figure. This lower insulating cone was internal to the apparatus and thus was not intended to cooperate with a cable termination. This was confirmed in particular by the fact that the standard F3 only specified the maximum dimensions h6, d7 of an envelope of the lower insulating cone. The cable connection parts shown in the upper portion of said figures of F3 each comprised a conical interface surface that was intended to be complementary to the interface surface of a cable termination. The dimensions d1, d2, h2 given in document F3 for the different apparatus connection parts specified therein resulted in angles Alpha defining these conical interface surfaces having values between 0.895° and 5.95°. These values were well outside the range defined in claims 1 and 2 of the patent in suit. Thus, document D3 was not relevant against claim 1 or 2. In particular, it did not destroy the novelty or inventiveness of the claimed range between 15° and 45°.

Document E5 disclosed the closest prior art. E5 described a device for interconnecting a high voltage cable with an apparatus, comprising a cable termination, which consisted of an elastomeric body having a conical interface surface, and a rigid insulator having a conical interface surface complementary to the interface surface of the cable termination. It could be seen from Figure 1 of E5 that the angle defining the conical surface of the rigid insulator was approximately 10°. Thus, E5 did not suggest a range between 15° and 45°. The object of the invention of the patent in suit was to provide a simplified connection system for cables having ratings up to 400 kV and more. More precisely, the object of the invention was to standardize and optimise the connection, in particular provide a single simplified connection for high voltage cables, especially above 36. kV, with a conical insulator having the same angle Alpha for every voltage. With an increase in voltage, the interface had to be made longer to increase the leakage creeping path. However, the angle Alpha was chosen based on other considerations. An angle Alpha between 15° and 45° provided the best possible compromise between the dimensional, electrical and mechanical properties of the device. In particular, because the resistance at the elastomer-epoxy interface was lower than inside these two materials, it was advantageous to reduce the tangential component of the electrical field at the interface. For a simple configuration, this tangential component was given by sin (Alpha) and was substantially reduced for values of Alpha lower than 45°. For small values of Alpha, lower than 15°, the height of the device increased very rapidly, which made the device too bulky. Furthermore, due to the high friction coefficient of the elastomer, lubricant had to be used abundantly during assembly. The lubricant tended to be absorbed, so that, due to the increased friction, disassembly required a large force to separate the parts. By increasing Alpha, it was possible to reduce the required force and diminish the quantity of lubricant, while keeping a relatively small height. Thus, the choice to have an angle Alpha between 15° and 45° as specified in claims 1 and 2 of the patent in suit was not arbitrary, but had a technical significance. Furthermore, none of the cited prior art documents suggested having an angle Alpha between 15° and 45°. Indeed, at very high voltages, other manufacturers used an angle Alpha = 0° or a hollow insulator filled with a dielectric fluid, in general oil. The subject-matter of claims 1 and 2 of the patent in suit thus involved an inventive step.

VI. The respondent essentially argued as follows:

Figure 1 of document E5, which disclosed the closest prior art, showed a device interconnecting a high voltage cable with an apparatus. The cable termination consisted of an elastomeric body, which had a conical interface surface, and a metallic cover. A rigid insulator having a conical surface complementary to the interface surface of the cable termination was provided on the side of the apparatus. The subject-matter of claim 1 of the patent in suit differed from this prior art device in particular in that a stress relief device and a connector shield were integrated in the elastomeric body of the cable termination. As appeared from column 2, lines 29 to 36, of the patent in suit, this stress relief device was in fact a stress relief cone comprising a voltage deflector. A similar conical voltage deflector 5 was already included in the rigid insulator 3 shown in Figure 1 of E5. Furthermore, a similar element 105 was included in an elastomeric body 103 shown in Figure 2 of E5. Document E3 also showed such a voltage deflector 18 integrated in a body made of silicone rubber. It was therefore obvious to the skilled person to include such an element in the elastomeric body of the cable termination. Figure 1 of E5 also showed a metal lattice 9 integrated in the rigid insulator 3 and it was obvious to the skilled person to provide such a lattice also in the cable termination as a connector shield. Thus, all the components mentioned in claim 1 of the patent in suit were obvious. The object of the invention described in E5 was to reduce the length of the connection and the particular device shown in Figure 1 of E5 was intended for operation at a voltage of 20 kV. It was obvious to reduce the length of the connection at higher voltages by increasing the angle defining the conical interface surface, thereby flattening the conical interface. Furthermore, document F3 showed a trend to increase the angle defining the conical interface as well as the height of the device with increasing voltage. Thus, at higher voltages, the skilled person would not only increase the height of the device but also the angle Alpha. In particular at a voltage of 400 kV as envisaged in the patent in suit, Alpha would necessarily be greater than 15°. Therefore, the subject- matter of claim 1 of the patent in suit was obvious in view of either E5 alone or a combination of E5 and E3. The components specified in claim 2 of the patent in suit were obvious in view of document E3, which disclosed a device with two plugs 21, each having a conical interface surface, and an elastomeric body 8 with a connector shield integrated therein and an outer conductive screen 19, wherein the body had two conical interface surfaces complementary to conical interface surfaces of the plugs. The figure in the upper part of page 2 of document F2 also showed an elastomeric body 2 with a connector shield 5 integrated therein and an outer conductive screen 1, which body had two conical interface surfaces for receiving rigid insulators having complementary interface surfaces. Due to the trend to higher voltages and the desire to keep the connection short, it was obvious to have an angle for the conical interface surfaces in the range between 15° and 45°. Furthermore, the angle would necessarily have to be made larger if the length of the device was to be reduced. It was correct that the invention of the patent in suit aimed at standardising and optimising. However, this did not mean that the invention involved an inventive step. The skilled person would increase the angles resulting from the DIN standard (document F3) when standardising the connection at higher voltages.