Restoration of the dielectric properties of in-service electrical power cables is well known. The general method comprises injecting a dielectric enhancement fluid into the interstitial void space associated with the conductor geometry of the cable. Typically, the injected fluid is an organoalkoxysilane monomer which subsequently diffuses radially outward through the polymeric insulation jacket to fill the deleterious micro-voids (“trees”) which form therein as a result of exposure to high electric fields and/or adventitious water. The organoalkoxysilane can oligomerize within the insulation, the shields, and the interstitial void volume of the cable by first reacting with adventitious water. In the case of in-service cables, as defined below, water can be present in the conductor strands as well as the intermolecular spaces of the polymeric components and fillers associated therewith (e.g., carbon black for most conductor and insulation shields; clay for most rubber insulation formulations). Water can also reside in micro-voids formed during manufacture of the cable and those formed during aging (e.g. water trees and halo). Furthermore, water can also diffuse into the cable from the environment. Oligomerization of the organoalkoxysilane retards the exudation of fluid from the insulation and micro-voids of the cable. An early method of this type, wherein the dielectric enhancement fluid was an aromatic alkoxysilane, was described by Vincent et al. in U.S. Pat. No. 4,766,011. This disclosure teaches the optional inclusion of a “hydrolysis condensation catalyst” as a part of the treatment fluid formulation to promote the above-mentioned oligomerization. A variation of the '011 patent method, which employs a mixture of an antitreeing agent, such as an organoalkoxysilane, and a rapidly diffusing water-reactive component as the dielectric enhancement fluid, also teaches the inclusion of such a catalyst, albeit with less emphasis. This method has enjoyed commercial success for more than a decade (see U.S. Pat. No. 5,372,841).
However, even though the above patent references recognized the benefit of including a catalyst and the importance of preventing the exudation of the dielectric property-enhancing fluid from the cable, they only disclose the use of certain organometallic catalysts.
USPTO Backgrounds
USPTO Backgrounds