CONNECTOR FOR CONNECTING A THREE-PHASE CABLE AND MANUFACTURING METHOD OF THE CONNECTOR

Abstract: The invention relates to a connector and a manufacturing method thereof for a three-phase cable comprising concentric, segmentally disposed phase conductors (1) with surrounding insulation structures (11) and a concentric earth conductor (8) enclosing the phase conductors. According to the invention, the phase conductors (1) inside the connector are isolated from each other by means of a star-shaped dividing insulation piece (3) keeping the phase conductors (1) separate in their segments, phase terminals (2) of the connector being disposed on the segment bottoms of said dividing insulation piece (3), the connector further incorporates clamp means (5, 7) suited for pressing the phase conductors (1) against the phase terminals (2), and the connector further incorporates a ferrule (10) on which the earth conductor (8) can be bent backward and with the help of which the connector can be mechanically locked to a receptacle.

Description: Connector for connecting a three-phase cable and manufacturing method of the connector The present invention relates to a connector according to the preamble of claim 1 for connecting a three-phase cable. The invention also concerns a manufacturing method for the connector. Connection of a three-phase squirrel-cage or synchronous motor in inverter-driven systems is most frequently performed by means of a copper or aluminium cable having three symmetrically placed phase conductors surrounded by a common concentric earth conductor. Connection to the drive acting as the load is conventionally performed using a terminal block at low current levels and cable lugs at higher current levels. The concentric earth conductor is bundled into a "tail" diverted from the side of the cable and then connected using either of the above-mentioned termination methods. Such a termination method has several shortcomings. Firstly, the joint unavoidably becomes long and bulky, because the phase conductors must be diverted apart from each other prior to the jointing. Secondly, at least four separate jointing steps must be carried out, three for the phase conductors and one for the earth conductor. In the case of segmental phase conductors, they must be dressed into a round shape before jointing. Besides the connections, the cable must be secured by means of a separate strain relief. The phase and earth conductors, which are diverted apart from each other for the connection, form loops and radiating dipoles for the currents passing through them thus giving rise to stray inductances and emission of electromagnetic fields to their surroundings. To avoid such interference, the phase conductors should be arranged to run as symmetrically and as close to each other as possible. Furthermore, the length of the phase conductors exposed from under the concentric earth conductor should be minimized. It is an object of the present invention to overcome the drawbacks of the above-described technology and to provide an entirely novel connector for connecting a three-phase cable and a method for manufacturing such a connector. The goal of the invention is achieved by means of provid- ing a purpose-designed symmetrical connector for connect¬ ing a cable in inverter-driven systems, in which connec¬ tor the insertion of all three phase conductors into the connector occurs in a single jointing step and the earth connector is continued in its concentric form into the interior of the connector housing. Simultaneously, the concentric jointing of the earth conductor acts as the strain relief for the cable. More specifically, the connector according to the inven- tion is principally characterized by what is stated in the characterizing part of claim 1. Furthermore, the method according to the invention is principally characterized by what is stated in the char- acterizing part of claim 3. The invention offers significant benefits. Jointing can be made in a single step. At the same time the jointing step provides an effective strain relief. Moreover, the embodiment according to the invention provides an electrical interference level much lower than that of conventional constructions. In the following the invention will be examined in greater detail with reference to exemplifying embodiments illustrated in the appended drawings in which Figure 1 is a side view of a connector according to the invention; Figure 2 is a cross-sectional view along the plane A-A of the connector shown in Fig. 1; Figure 3 is a cross-sectional view along the plane B-B of the connector shown in Fig. 1; Figure 4 is a cross-sectional view along the plane C-C of the connector shown in Fig. 1; Figure 5 is a cross-sectional view along the plane D-D of the connector shown in Fig. 1; and Figure 6 is a cross-sectional view along the plane E-E of the connector shown in Fig. 1; Referring to Figs. 1 - 6, the connector according to the invention and the manufacturing method thereof are now described. In contrast to conventional jointing methods, the phase conductors 1 of the cable will not be diverted apart for connection under parallel terminals; instead, they are left in their natural positions and inserted unbent into a purpose-designed connector having a concentric structure, wherein the individual phase conductors l are disposed into circularly symmetrical segments of 120°. Referring to Fig. 6, the bottom in each segment terminal of the connector is shaped into a contact terminal 2 which is suited to make electrical contact with a phase conductor 1 and is continued as an isolated bar in the connector body and is finally connected to an inverter drive using appropriate means. The stripped lengths of the phase conductors 1 are radially compressed toward each other by means of a clamp 5 resembling a conven¬ tional hose clamp so as to provide good electrical contact between the phase conductors 1 and the segment terminals 2. Between the clamp 7 and the phase conductors 1 are adapted insulation pieces 4 and springed elements 6. The springed elements find use in the connection of aluminium conductor cables. Typically, the springed element 6 is a wave plate of spring steel to be placed between the clamp 7 and the insulation piece 4. The connector is typically encased in a metallic housing acting as an EMI shield, whereby the concentric earth conductor 8 is clamped to the feedthrough flange of the housing by means of a ferrule. The completed connection of the cable retains full symmetry and offers the best possible protection against EMI. The work stages of connector manufacture are as follows: 1. Starting from the end of the cable, the plastic sheath 9 acting as insulation is removed over a length of approx. 50 - 150 mm, advanta¬ geously approx. 90 mm such that the concentric multiwire copper earth conductor 8 is exposed. A steel ferrule 10 is inserted onto the exposed length of the concentric conductor, at its very stem, onto which ferrule all the separate copper wires of the earth conductor are bent backward. The copper wires are trimmed at the point where the ferrule 10 rests against the plastic sheath 9. This arrangement serves for strain relief and direct connection of the earth conductor to the metallic body of the adapter-type connector. 2. Insulating plastic wrappings 11 covering the phase conductors 1 are removed and the ends of the segment-shaped phase conductors 1 are stripped free over a length of approx. 5 - 50 mm, advantageously approx. 20 mm. For an aluminium conductor cable, oxide is removed from the inner surfaces of the conductor in a conventional manner applying contact grease if necessary. Outward bending of the phase conductors 1 is kept to the minimum save for the insulation and oxide removal steps of the conductors. At this stage, the cable end is ready for termination. 3. The exposed cable end with the segment terminals is pushed so deep into the connector as to align the earth conductor ferrule 10 with the center of the feedthrough flange of the EMI shield housing. 4. The phase conductors 1 are compressed against the segment terminals 2 with the help of the clamp 5 using a torque-indicating wrench to determine the proper tightening torque. 5. Finally, the upper part of the EMI shield housing is attached in place such that the earth conductor 8 of the cable remains compressed inside the feedthrough flange, whereby reliable electrical connection and good strain relief are established. In the context of the invention, the EMI shield housing can be appropriately called the receptacle of the connector.

Claims: Claims: 1. A connector for a three-phase cable comprising concentric, segmentally disposed phase conductors (l) with surrounding insulation structures (11) and a concentric earth conductor (8) enclosing the phase conductors, c h a r a c t e r i z e d in that - the phase conductors (1) inside the connector are isolated from each other by means of a star-shaped dividing insulation piece (3) keeping the phase conductors (1) separate in their segments, - the phase terminals (2) of the connector are disposed on the segment bottoms of said dividing insulation piece (3) , - the connector further incorporates a clamp means (5, 7) suited for pressing the phase conductors (1) against the phase terminals (2) , and - the connector further incorporates a ferrule (10) on which the earth conductor (8) is bent backward and with the help of which the connector can be mechanically locked to a receptacle. 2. A connector as defined in claim 1, c h a r a c - t e r i z e d in that said clamp means comprise a clamp ring (7) and a clamp (5) proper. 3. A connector manufacturing method for a three-phase cable comprising concentric, segmentally disposed phase conductors (1) with surrounding insulation structures (11) and a concentric earth conductor (8) enclosing the phase conductors, in which method the phase conductors (1) are electrically connected to electrical terminals (2) communicating with an electrical load and the cable end is stripped of the insulation material (9) enclosing the earth conductor (8) , c h a r a c t e r i z e d in that - a steel ferrule (10) is inserted onto the earth conductor (8) , at its very stem, on which ferrule all the separate copper wires of the earth conductor (8) are bent backward and the wires are trimmed at the point where the ferrule (10) rests against the plastic sheath (9) , - the insulation (11) covering the phase conductors is removed and the ends of the phase conductors (1) are stripped, - the exposed cable end with segment terminals is pushed so deep into the connector as to align the ferrule (10) of the earth conductor (8) with the center of the feedthrough flange of the body structure of the connector receptacle, - the phase conductors (1) are pressed against the segment terminals (2) with the help of clamp means (5) , and - finally, the connector is attached to the receptacle so that the earth conductor (8) of the cable remains pressed against the feedthrough flange, whereby reliable electrical connection and good strain relief are established. 4. A method as defined in claim 3, c h a r a c t e r ¬ i z e in that the insulation of the earth conductor (8) is removed over a length of approx. 50 - 150 mm, advantageously approx. 90 mm. 5. A method as defined in claim 3, c h a r a c t e r - i z e d in that the insulation (11) of the phase conduc¬ tor (1) is removed over a length of approx. 5 - 50 mm, advantageously approx. 20 mm. 6. A method as defined in claim 3 for completing the connector for an aluminium cable, c h a r a c t e r ¬ i z e d in that oxide is removed from the inner surfaces of the phase conductors (1) in a conventional manner applying contact grease if necessary.

Inventors: MIETTINEN ERKKI, MIETTINEN, ERKKI
Applicants: ABB INDUSTRY OY, MIETTINEN ERKKI, MIETTINEN, ERKKI
Application year: 1995
Main classification: H01R4
IPC codes: H01R4, H01R9, H01R13, H01R24