Investigation and Mitigation of Insulated Joint Electrical Failure: A Guide (2025)
Chapter: 2 Background
CHAPTER 2
Background
Problem Statement
Transit agencies use electrical traction (overhead catenary or third rail) for the propulsion of trains, which is typically designed using high-voltage AC or direct-current (DC) electricity. The running rails are used as part of the system to return negative power to the traction power substation (TPSS). IJs are trackwork components installed in the rails to provide a train control circuit and traction power segment separation between blocks. IJs are implemented in the design of freight and transit railroads, which operate in vastly different system environments. Freight railroads are typically designed to use low-voltage/low-amperage train control systems with diesel power, while transit is typically designed to use train control systems that function in high-voltage/high-amperage traction power negative return (TPNR) systems.
Scope of Study
The emphasis of this work is related to DC-electrified transits and railways that are experiencing IJ failures, with a special focus on systems that use vehicles with AC traction motors. Although IJ arcing can occur on electrified railways with AC power distribution systems, the mitigation efforts are very different from those for DC systems and are outside the scope of this work; however, this guide may provide some useful information to those with AC distribution systems.
The primary deliverable for TCRP Project D-20 is this guide. The scope of work required to produce this guide included a literature review (see Appendix G), an industry survey (see Appendix E), and the preparation of a summary of gaps and needs in the current state of knowledge or practice where further research is needed (see Appendix F).
Additional work, performed as a part of this project but not included in this guide includes the following: creation of an initial amplified research plan for project panel review and comment, preparation of a separate technical memorandum titled “Implementation of Research Findings and Products,” compilation and delivery of monthly and quarterly reports, and support of project panel meetings.
Key Findings
- IJ arcing is not necessarily caused by the IJ—it is typically a symptom of other underlying issues.
- Common deterioration of the IJ and IJ rail ends can contribute to IJ arcing issues that can be easily mitigated by properly maintaining IJs and TPNR electrical bonding cables and cable connections.
- Some IJ arcing issues may require a multidisciplinary effort to resolve.
- The use of AC traction motors alone does not cause IJ arcing.
- Regenerative braking may contribute to IJ arcing.
- Introducing new vehicle fleets that impose additional loads on the TPNR system can result in IJ arcing.
- Increased traction power loads also increase TPNR loading that can result in IJ arcing; these include
- Changes to train operations and
- New or upgraded vehicles.
- Using computer models that do not detail the TPNR system in the track for traction power design may result in misleading results and conditions that can lead to IJ arcing.
- Inadequate integration in the design or modifications that affect the TPNR system can result in IJ arcing.
