Electrical connectors – Metallic connector or contact having movable or resilient... – Screw-thread operated securing part
Reexamination Certificate
2000-01-13
2001-05-15
Donovan, Lincoln (Department: 2839)
Electrical connectors
Metallic connector or contact having movable or resilient...
Screw-thread operated securing part
C439S801000, C439S812000, C439S921000
Reexamination Certificate
active
06231404
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a connector for an insulated cable. The connector is intended for medium-voltage cables insulated with solid insulation and adapted for distribution networks up to 36 kV. The connection is adapted for current supply to switchgear or transformers for currents up to 250 A.
BACKGROUND ART
The task of a connector is to ensure an electrical connection between a cable and electric equipment. From patent document EP 0 655 805 A1, a connector is previously known, which shows a connector surrounded by an insulating body protected against hazardous contact. According to the known connector, the cable core is inserted into a sleeve-shaped contact shoe. In the side of the contact shoe, a hole is provided, into which a pin contact is threaded. The pin contact has a tool adaptor, which is provided with a notch. Upon reaching a torque, corresponding to a definite contact pressure on the cable core, the tool adaptor is arranged to be sheared off. The pin contact presses laterally against the exposed cable core and secures the cable core between the pin and the contact shoe. In so doing, the pin contact exerts a pressure only on some of the individual wires of the cable core.
The above-mentioned known connector solves the task of ensuring electrical connection in a complicated way. One problem is that the conductor wires are exposed to a local displacement such that they make contact with one another with such a force that they are deformed and hence damaged. By the different mechanical stresses on the conductor wires, different contact resistance and hence a non-uniform electrical stress on the cable core arise in unfavorable cases.
A further problem with the known connector is that the joint is not detachable, since, on the one hand, the tool adaptor is broken off and, on the other, the conductor wires are deformed during mounting. During repair or replacement of such a connector, the deformed end of the cable core must be cut off and the entire cable must be prepared anew, which requires a new effort. Nor does the known connector permit any reuse.
A disadvantage of the known connector is also that the pin contact, depending on the depth of screwing into the contact shoe, extends to differing degrees into a corresponding connection device in the equipment. Different thicknesses of the cable core therefore lead to differently sized contact surfaces being exposed in the pin contact.
An additional problem exists in the known connector, when measurement of the ground resistance of the cable screen is to be carried out. Usually, the outer conducting casing of the connector is connected to both the ground connection in the equipment and to the grounded cable screen. This ensures both mechanical protection and protection against hazardous contact, as well as a potential balance. To measure the ground resistance of the cable screen, this must be disengaged from all connection with ground or the outer conducting layer of the cable. For this purpose, the outer casing must be at least partly dismantled, which is time-and work-demanding.
To guarantee safe operation, the connector must be connected in an unseparable way with a bushing in the equipment. For this purpose, the connector must be held in contact position against the bushing. In bushings in the equipment there are eyes for attachment of a clamp making contact with the connector. Such a clamp exerts a pressure on the connector casing in a direction towards the equipment and hence fixes the connector in its contact position.
Known clamps usually consist of several parts and are relatively costly to manufacture. Usually, the clamps are applied with the aid of clamping screws which are tightened during mounting. It also occurs that the connector is held in position with the aid of springs which exert a clamping force over a yoke which makes contact with the connector.
SUMMARY OF THE INVENTION
The object of the invention is to provide a screened connector for current supply between, for example, a switchgear unit or a transformer and a medium-voltage cable, insulated with solid insulation, for distribution networks up to 36 kV. The connector is intended for indoor environments and to transmit currents up to 250 A. The cable core is subjected to less mechanical stress than known connectors. Measurement of the ground resistance of the cable screen in an installed connector is made possible. The connector permits a simple and electrically safe installation and is cost-effective. In addition, the electrical connection shall is capable of being dismantled and the parts are reusable. The disadvantage of the above-mentioned prior art design is avoided and the work and time expenditure during installation is reduced.
This is achieved according to the invention by a connector as described hereinafter. Advantageous embodiments are also described.
The connector according to the invention comprises a connection device arranged in an elastic insulating angular housing. The connection device comprises a clamping block placed in the angular housing, a pin contact being threaded in the side of the clamping block. A guide sleeve encloses the deinsulated end of the cable core and has an extension designed as a jaw. The jaw is inserted into the clamping block, the clamping block thus enclosing both the jaw and the cable core. The pin contact makes contact with the jaw and exerts, when being screwed in, a pressure against the jaw such that the cable core is clamped between that side of the clamping block, which is opposite to the pin contact, and the jaw. The contact pressure is thus evenly distributed over the conductor wires of the cable core end.
The thermal expansion of the cable core varies with different load states. The side parts of the clamping block are hence designed so thin that they become resilient when the cable core is expanded. In this way, a compressive force, which is partly independent of thermal variations, is created across the cable core. The necessary prestress pressure may thus be reduced to a minimum.
In a connector according to the invention, the pin contact always adopts the same contact position in the housing opening, independently of the depth of screwing. In this way, the plug-in depth and hence the contact surface for the pin contact will always be of the same magnitude, independently of the thickness of the connected cable core.
The angular housing is made of an elastic material and comprises several layers. The required potential equalization is achieved by constructing the outer layer of the housing of a semiconducting material and connecting it to the cable screen and to the ground of the equipment. Because of the elastic construction of the housing, it is possible to fold up that end of the housing which is connected to the cable and roll it backwards. This permits the connection between the cable screen and the outer casing of the connector to be separated. Measurement of the ground resistance of the cable screen and hence inspection of the cable sheath may thus be performed in a simple manner without separating the connector.
The connector is held in its contact position by a clamp which is made in one piece. The clamp is made of an elastic material, for example of a wire of spring steel and designed so as to receive a small spring constant with great capacity of movement. This is fulfilled, for example, if the clamp is brought to include at least one helical spring. In this way, the clamp may be easily clamped by hand. The spring force achieved is sufficient to securely fix the connector in its position in the equipment.
REFERENCES:
patent: 2916720 (1959-12-01), Steans
patent: 4427258 (1984-01-01), Mueller
patent: 4812012 (1989-03-01), Norden
patent: 5000705 (1991-03-01), Kinka et al.
patent: 6011218 (2000-01-01), Burek et al.
patent: 3029904 (1982-03-01), None
patent: 3210223 (1983-09-01), None
patent: 3543596 (1986-06-01), None
patent: 0655805 (1994-11-01), None
patent: 0691721 (1995-06-01), None
patent: 2503939 (1982-10-01), None
patent: 2216737 (1989-10-01), None
ABB AB
Connolly Bove & Lodge & Hutz LLP
Donovan Lincoln
Prasad Chandrika
LandOfFree
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