Material Evaluation: Self Damping Wire SD/ACSR Conductor Failures

Power District (NPPD) implemented an inspection program to determine the extent of condition for this type of widely used conductor. Other companies which have had related issues with similar types of corrosion have simply replaced their existing insignificant miles of conductor; however NPPD transmission system includes over 2000 miles of this particular conductor. Throughout 2012, many other conductor spans were discovered with either broken or missing steel wire in the bundled conductor. Transmission line splices are installed every 15-20 spans, with failures being located in a span containing a splice. NPPD worked with Kinectrics to complete electromagnetic field inspections for three days in 2013, with retesting performed in 2015. Throughout this inspection of 54 spans of conductor, 36 were found to have some level of deterioration/corrosion ranging from marginal (5) to fair (1) to good (30). Over 80% of the corrosion noted in the report was found on a conductor span containing a splice; only 45% of the spans tested contain a splice. All of the failures occurred in spans where a compression sleeve or compression dead-end was present. In all cases, only the steel core broke internal to trapezoidal aluminum wire layers. The results of the inspection indicated that there is a notable amount corrosion in more than 50% of the spans inspected, mainly located in the middle 300 feet of the span. The corrosion is " marginal " in a few locations, but generally not indicative of an acute problem. Removal of spans testing " marginal " occurred in April 2015, along with the physical evaluation of the conductor validating the results of the electromagnetic inspection tool. Broken strands were found in all of the tested conductors scored as " marginal " following removal 2 years after initial testing. None of the conductors were rated as poor, which would indicate no imminent failures exist. Since none of these localized areas were in poor condition, it could be several years before more frequent findings of broken wire and related problems are observed.