NEW APPROACHES TO FLUID BLOCKING.

Abstract : The influence of the filling compound on the electrical characteristics of plastic-insulated multi-pair cables was studied theoretically. It is concluded that there is a strong economic incentive to find a method of blocking these cables against ingress of moisture with a filling compound of low dielectric constant. Successive amounts of water were injected into an unfilled cable so as to reveal the mechanism by which water affects the capacitance and conductance of the cable pairs. The concept of blocking these cables by means of hollow plastic microspheres, held in a fluid or solid matrix, is next introduced. The characteristics of one type of microsphere, which is commercially available, and of some fluid hydrocarbons loaded with these microspheres are described. Tests have been made to show the influence of these filling compounds on the mechanical properties of the insulating and jacketing materials used in this class of cable. Attention is drawn to the need for more revealing test procedures so that their long-term effects can be predicted with more precision. Some technical advantages are seen to lie in the use of specific polyethylene grease compounds, both as a filling medium and as a carrier for hollow microspheres. (Author)