High voltage cable EMI shield

#The present invention is related to corona chargers, and more particularly, to shielding of high voltage cables between the high voltage source and the charger assembly.

#Corona chargers generate high frequency emissions that need to be suppressed by the shielding of high voltage cables. This suppression may be required for compliance with applicable electromagnetic emissions regulations and/or system functional requirements. In some applications a fully shielded solution is not required. A simple return path coaxial with the high voltage wire between the power source and the corona charger is all that is necessary. If the shield is placed close to the conductor there will be corona emissions and/or capacitive current through the high voltage wire insulation. This current loss through the insulation is typically in the range of tens to hundreds of microamps. In many electrophotographic charging applications current regulated power supplies are used to drive the charging systems. Typical current regulated chargers operate in the range of 100-2000 microamps. The loss of small amounts of current through unintended paths, such as through the shield, reduces the effectiveness of the system. Corona current flow from wire to shield reduces the efficiency of the system and degrades the insulation system resulting in lower reliability.

#Electrophotographic printing machines are built in a variety of physical configurations requiring many different high voltage cable routings. It is desirable to have a shielding system that can easily be adapted to different lengths and shapes. A simple flexible shielding system that can provide a consistent minimum space between the high voltage conductors and the shield is required.

#FIG. 1 is a cross sectional view of the shield, spacer and cable configuration;

#FIG. 2 is a longitudinal cross sectional view of the shield, spacer and cable configuration;

#FIG. 3 is a view of the preferred embodiment of the invention showing the grounding connections of the shield; and

#The invention provides a method and apparatus for shielding high voltage cables while reducing current flow to the shield, by adding a continuous foam spacer between the high voltage conductor and the grounded conductive shield. The teachings of Ditscheid do not present a simple, flexible assembly for adding a spaced shield to existing common low power, high voltage wiring. The present invention provides a flexible assembly with a simple process for adding a spaced shield to existing common low power high voltage wiring. The present invention also eliminates loses by providing a spacer between the center conductor and the shield along the entire length of the shield, thus eliminating the problem at the termination that Reif addresses.

#Referring to FIG. 1 in conjunction with FIG. 2, it has been discovered that problems associated with corona discharge through the insulation to the shield 1 are eliminated by the addition of a flexible spacer 2 between the insulated high voltage conductors 3 and the shield 1. FIG. 1 illustrates an axial cross sectional view for the preferred configuration of the invention. FIG. 2 is a longitudinal cross sectional view of the shield 1, spacer 2 and conductor 3 shown in FIG. 1. Preferably, an insulating foam tube is wrapped with a conductive shield 1.

#FIG. 3 is a view of the preferred embodiment of the invention to illustrate the grounding connections employed for the shield 1. The shield 1 is grounded via the integral ground tabs 4 as shown in FIG. 3, the shaded area is the conductive shield 1 and the grounding tabs are, preferably, formed by heat-sealing the fabric. As seen in FIG. 3, the fabric used to make shield 1 is wrapped around the continuous spacer 2. In the preferred embodiment, shield 1 is made from a Schlegel® Silver C2 fabric, although numerous types of conductive fabric can be used for shield 1. The shield 1 is preferably grounded at both ends. One end of the shield is connected to the power supply case ground. The other end of the shield is connected to the ground reference surface of the corona charger.