Patent Publication Number: US-4222625-A

Title: High voltage electrical connector shield construction

Description:
The present invention relates generally to shielded high voltage electrical connectors and pertains, more specifically, to a shield construction which enables use of such a connector at higher voltages without the presence of the deleterious effects of corona when the connector is unconnected and is energized under high voltage conditions. 
     In recent years, heavy emphasis has been placed upon the development of underground electrical power distribution systems, especially in light industrial, commercial and residential areas. Various power distribution components, such as shielded high voltage electrical cables, transformers and electrical connectors have been evolved for use in such systems. Among these components, shielded electrical connectors have been developed which are assembled early in the field at the terminal ends of electrical cables so as to facilitate the construction and installation of underground power distribution systems. The numerous advantages of such connectors have given rise to the demand for simplified connectors which will operate successfully at even higher voltages than those already accommodated by earlier connectors. 
     Devices have been developed which enable the safe connection or disconnection of shielded high voltage electrical connectors, such as a connector elbow, with a high voltage terminal, such as a bushing, under load conditions. However, in operations at higher ratings, in excess of 35 Kv, for example, corona can develop in the energized unconnected connector due to the high electrical stresses across the gap between the contact pin and the shield of the unconnected connector. The result is an undue amount of noise, as well as other deleterious effects. 
     It is an object of the present invention to provide a shielded electrical connector for high voltage connections, the connector having a shield construction which reduces the electrical stresses between the connector contact and the connector shield while the connector is unconnected and is energized under high voltage conditions. 
     Another object of the invention is to provide a shielded electrical connector having a simplified shield construction which eliminates or reduces corona noise in an unconnected connector which is energized at higher voltages. 
     Still another object of the invention is to provide a shielded electrical connector of the type described and capable of ready installation in the field at the terminus of a high voltage power distribution cable. 
     Yet another object of the invention is to provide a shielded electrical connector of the type described and having a structure compatible with present related components. 
     A further object of the invention is to provide a shielded electrical connector of the type described and having a construction which enables ready fabrication utilizing present manufacturing techniques. 
     A still further object of the invention is to provide a shielded electrical connector of the type described which is economically fabricated in large numbers of uniform high quality. 
     The above objects, as well as still further objects and advantages, are attained by the present invention which may be described briefly as providing, in a shielding system for an electrical connector having a housing including a first end for engagement with a high voltage electrical cable and a second end carrying an electrical contact element for connection with a high voltage terminal, the improvement comprising: a shield extending along the housing, the shield including a first portion adjacent the first end of the housing and a second portion adjacent the second end of the housing; and the second portion of the shield being electrically separated from the first portion such that the electrical potential difference between the contact element and the second portion of the shield, under energized conditions, will be less than the electrical potential difference between the contact element and the first portion of the shield. 
    
    
     The invention will be more fully understood, while still further objects and advantages will become apparent, in the following detailed description of a preferred embodiment illustrated in the accompanying drawing, in which: 
     FIG. 1 is a longitudinal, cross-sectional view of an electrical connector constructed in accordance with the invention, installed at the terminus of a high voltage electrical cable and about to be connected to a high voltage terminal; and 
     FIG. 2 is a fragmentary view of the components of FIG. 1, connected. 
    
    
     Referring now to the drawing, an electrical connector constructed in accordance with the invention is illustrated in the form of connector elbow 10 which is about to be connected to a high voltage terminal in the form of a bushing 12. Connector elbow 10 is installed at the terminus of a high voltage electrical cable 14 which has a conductor 16, insulation 18 and an external shield 20. 
     Connector elbow 10 includes a housing 22 which is installed over the end 24 of the shield 20, bared portion 26 of the insulation 18, and a terminal 28 which is electrically connected and mechanically secured to conductor 16 of cable 14 by means of a crimped connection between the barrel 30 of terminal 28 and the conductor 16. Housing 22 extends axially between a first end 32 and a second end 34 and is molded of elastomeric materials. A first member 36 of housing 22 is molded of an insulating elastomer and extends throughout almost the entire length of housing 22. An external shielding system is provided by a shield 38 constructed of a conductive elastomer in the form of second and third members 40 and 42 molded integral with first member 36. An internal shield is provided by a fourth member 44 of conductive elastomeric material molded integral with the first member 36. 
     Housing 22 is installed readily at the terminus of cable 14 in a now well-known manner. That is, housing 22 is slipped over the cable terminus so that the first member 36 grips the bared portion 26 of insulation 18 and second member 40 grips the cable shield 20 adjacent the first end 32 of the housing to establish the appropriate insulated connection while continuing the shield along the housing. An electrical contact element in the form of a conductive pin 46 is secured to the terminal 28 by means of a threaded connection 48 and extends axially within a recess 50 located adjacent the second end 34 of the housing 22 and extending axially into the housing to establish a receptacle for receiving the bushing 12. Pin 46 has given external diameter D which is complementary to the internal diameter of a socket 52 which serves as the electrical contact element of bushing 12. 
     Bushing 12 is the terminal of a high voltage transformer 54 and includes an insulator 56 surrounding the socket 52. When a connection is established between electrical connector 10 and bushing 12, as seen in FIG. 2, pin 46 makes contact with socket 52 and insulator 56 is seated within recess 50. An annular cuff 58 at the second end 34 of the housing 22 engages a complementary shoulder 59 of the bushing 12. 
     In the unconnected state illustrated in FIG. 1, the circuit which includes cable 14 and connector elbow 10 is energized so that connector elbow 10 is placed under high voltage conditions. Electrical stresses therefore are established across a gap 60 between contact pin 46 and shield 38, and especially between pin 46 and the shield 38 at portion 61 of cuff 58. In conventional connector elbows, the shield of the connector elbow is grounded and, when the circuit which includes the cable is energized, the electrical potential difference across the gap between the contact pin and the shield is a function of the potential at the pin and ground potential. Under high potential conditions, such as 35 Kv and upwards, the electrical stresses across the gap between the contact pin and the shield in a conventional connector elbow will cause corona. The corona engenders an objectionable crackling noise as well as other deleterious effects. 
     In order to eliminate the unwanted effects of corona in an unconnected connector, as illustrated at 10 in FIG. 1, when cable 14 is energized so that connector 10 is under high voltage conditions, the shield 38 is constructed in two portions, shown in the form of second and third members 40 and 42, with the third member 42 being separated electrically from the second member 40. In this manner, the third member is not grounded and the electrical stress across gap 60 is reduced. Thus, the second member 40, which extends axially from first end 32 toward second end 34 of housing 22 and circumferentially around first member 36, terminates at a terminal end 62, short of the second end 34, while the third member 42, shown in the form of a sleeve 64 also extending circumferentially around first member 36, extends axially from second end 34 toward first end 32 and terminates at a terminal edge 66 confronting terminal end 62 of second member 40 and is spaced axially therefrom. Sleeve 64 is coaxial with pin 46, has an inner surface 68 spaced radially from the pin 46 and from recess 50, and extends axially along a major portion of the axial length of recess 50. Because of the spacing between sleeve 64 and the remainder of the shield, in the form of second member 40, the sleeve 64 is separated electrically from the remainder of the shield. Hence, under energized conditions, with second member 40 grounded and pin 46 at a high electrical potential, the potential of sleeve 64 will rise, as a result of capacitance coupling between the pin 46 and sleeve 64, thereby reducing the potential difference between pin 46 and sleeve 64, with a concommitant reduction in electrical stress across gap 60. Corona is thereby reduced or entirely eliminated. 
     Because there will be a difference in electrical potential between sleeve 64 and second member 40, first member 36 is constructed to provide insulation between the second and third members 40 and 42. Thus, a portion 70 of first member 36 is placed between the confronting terminal end 62 and terminal edge 66. A further portion 71 of first member 36 extends axially along the inner surface 68 of sleeve 64 and terminates short of second end 34 to expose conductive portion 61 of cuff 58. Additionally, a sheath-like portion 72 of first member 36 extends axially along outer surface 74 of sleeve 64 to insulate against flash-over to the second member 40 and to protect operators against the voltage induced in sleeve 64, when the circuit is energized. 
     Upon connection of the connector elbow 10 to the bushing 12, as seen in FIG. 2, cuff 58 engages shoulder 59 and the cuff portion 61 of sleeve 64 makes contact with a grounded shield 78 on the bushing 12, bringing the entire shield 38 to ground potential. The spacing between the confronting terminal end 62 and terminal edge 66 is minimal and does not disturb the integrity and function of the shielding system in the completed connection. 
     The magnitude of the axial spacing between the second and third members 40 and 42 is great enough to assure that the second and third members 40 and 42 are electrically insulated from one another. However, the axial spacing should be kept small enough so as not to disturb the integrity and function of the shielding system in the completed connection. An appropriate magnitude for the spacing between the confronting terminal end 62 and the terminal edge 66 is of the same order of magnitude as diameter D of pin 46. 
     It will be seen that the structure of connector elbow 10 is changed only slightly from the construction of present, conventional connector elbows, but the change enables that structure to be used readily at higher voltages. Hence, the manufacture and use of connector elbow 10 can be accomplished economically and with ease, while attaining the advantages of extending the useful range of application. 
     It is to be understood that the above detailed description of an embodiment of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.