Failure of Overhead Line Catenary Wires
Synopsis
There had been several instances on the client's network of in-service failures of Overhead Line (OHL) catenary wires, necessitating unplanned maintenance and causing service delays. Our client required a diagnostic assessment of the root cause(s) of in-service failures and to reduce their risk in the future. Failed and intact samples were provided to Tata Steel for comparison and metallurgical investigation. Samples included two messenger wire bridle cables that had failed, and a third that exhibited damage where it passed over an aluminium pulley, which physically supported it.
Key Client Issues
Numerous occurrences of catenary wire failure at loading platforms had caused disruption to passenger services, and unplanned maintenance. The client needed to know the root causes so that action could be taken to prevent future occurrences.
Solutions
Laboratory examinations were carried out to determine the failure mode of the catenary wire. The presence of grease was observed on the failed and damaged cables.
The grease largely insulated the cable from the pulley except at isolated points of contact. Heating/arcing at these points of contact lead to the localised damage observed. Damage would increase over an extended time period, causing the wire to fray before eventual failure.
Tata Steel also established a variance between the bridle cable material and the specification. The material was found to be less ductile than if it had complied with the specification. However, brittle fractures of wire strands were not generally observed during the investigation. The variance from the specification appeared to be only a contributory factor rather than the root cause of failure, which was found to be electrical arcing. Corus' findings were presented in a report with conclusions on the mode(s) and root cause(s) of failure.
Client Benefits
Our report enabled the client to identify:
- That the main factor contributing to the failure was arcing taking place within the cable strands and between the cable and pulley. This was evident from the frayed wire samples.
- That the arcing damage was caused as a result of lubricant insulating one component from the other. Removing lubricant from the affected areas could rectify this.
- Discrepancies between the material specification and the material that had been supplied. This may have contributed to the failure.
