CHAPTER 4
Identification and Inspection

Field Inspections

When IJ arcing is discovered, methodical field inspections are the first step in mitigating the issue. Field inspections can easily identify the most common causes of IJ arcing, and the common causes often can be repaired quickly. If a simple deficiency is not found, field inspections can also yield information that may be useful in identifying the root causes of the issue. Details regarding how to identify, classify the severity of, and differentiate IJ arcing indications from unrelated rail end conditions can be found in Appendix A and Appendix D.

IJ Arcing Indications

Visual Inspection of Rail End Damage

IJ arcing can be easily identified by visual inspection. Visual indications of IJ arcing are generally the first item found that indicates other underlying issues. The appearance of IJ arcing on rail ends is unique and not easily confused with other possible rail surface conditions.

Estimating Current Visual Inspection

The severity of IJ arcing indicates the amount of current flow when the arcing event occurred. These visual cues can be useful in diagnosing the underlying issue and may point to the origin of the issue. TPNR is a network in the track. When IJ arcing is noted, the other IJs in the area should also be inspected. Other IJ arcing in the vicinity and the level of damage at those other IJs can provide insight on what is contributing to the IJ arcing and where the issues may have originated.

Metal Buildup on Rail Ends

The patterns of the metal deposits on the rail ends of arcing IJs can provide information on the direction of the current flow when the arcing occurred. The circuit from the TPSS that provides the power to the train will always be completed with that same TPSS. Any metal displaced by arcing will always flow from positive to negative. This indicates power flow from the propulsion power source (where the train is receiving the power from the third rail or OHC) to the TPSS that supplied that power ultimately generating the arcing for that train.

Many systems supply the traction power to a third-rail or OHC segment simultaneously from two different TPSSs, and a train could receive propulsion power from both. Ultimately, the power supply and return between the train and the TPSS will be proportional. The path of the return can be complex and can involve multiple different paths through the track, some of which may not be readily obvious. When IJ arcing occurs, the current will flow in a particular direction, which can be important in understanding the underlying cause(s) of and potential mitigations for the arcing.

Metal disposition indications can be masked by the passage of trains; passing train wheels will smooth the running surface of the rail. However, identifying the direction of flow can indicate where to look for possible contributing issues (see Appendix D).

Cables and Cable Connections

Loose TPNR cables and connections can result in IJ arcing. When arcing at IJs is found, all TPNR cables and connections in the area around the IJ should be inspected. The inspections should radiate out from the location of the arcing IJ and extend up to the cables that return the TPNR to the adjacent TPSSs, thereby providing traction power to the area. These cable connections, along with inspections of the IJs, are the simplest and quickest actions that can be taken when IJ arcing occurs.

Field Verification of Drawings

IJ arcing may be related to field installations that do not match the design or “as-built” drawings. It is not uncommon for field modifications to be made but not properly documented.

Drawings that detail the complete overall TPNR network on a specific set of drawings are uncommon. Various items that affect the TPNR system are commonly spread out over multiple drawing sets from various disciplines (e.g., track drawings, train control drawings, and traction power drawings). Many times, some of the details are standardized and shown on separate drawings, with simple notations made on detailed drawings that rely on the standard drawings. When field inspections are performed, the design drawings and field installations should be verified to ensure the installations match the design. Every detail that can affect the TPNR should be reviewed in the field, including items such as cable connections, cable bonds, cross bonds, the number of cables at each location, IJ locations, IJ layouts, and more.

The underlying cause of the IJ sparking may be related to installations that differ from the design. Inspections should include the entire TPNR system in the track, including cable connections and bonding, number of cables, IJ locations, IJ layouts, location of third-rail segments in relation to IJs, and more. Any items found to differ from the drawings in the field should be assessed regarding their contribution to IJ arcing.

Train Control System

Those responsible for train control system design and maintenance are crucial to resolving IJ arcing issues. The conditions that cause IJ arcing often can cause damage to the train control system. The damage to the train control system can be easily attributed to unrelated causes other than IJ arcing. Whenever IJ arcing is encountered, it is important to involve train control personnel, so all the issues and impacts can be identified. In many cases, this involvement will lead to the resolution of the IJ arcing issue.

The train control system is integral to the TPNR system. Compromises are often made in the design of the TPNR system to accommodate the train control system. This does not place the cause of IJ arcing onto the train control system if the train control system does not have sufficient energy to cause IJ arcing.

When investigating IJ arcing issues, the delicate balance between the TPNR system and the train control system must be considered. The placement and layout of IJs is crucial to the safe and proper functioning of the train control system. The locations of cable connections between running rails needed for the TPNR are affected by the design and functionality of the train control system.

Train Operations

Train operations are integral with the TPNR system. Understanding the operating environment when IJ arcing occurs can aid in determining why the arcing is occurring. Unless there is a deficiency in the insulation, IJs do not spontaneously arc; instead, the arcing is initiated by a passing train. Visual indications of arcing are found on the trailing rail end of the IJ, based on the direction of train movement. Evidence of arcing found on both rails typically indicates arcing that occurs when trains pass over the IJ in both directions.

IJ arcing can be a transient event and may not occur with the passage of every train. Additionally, the issues contributing to IJ arcing may result from occurrences at a different location than the arcing IJ (e.g., the location of a different train or the propulsion modes of those trains). For example, a train bridging an IJ at a different location might create conditions in which IJ arcing can occur when a train passes over a different location. IJ arcing might occur only when multiple trains are in a certain area or if one or more trains are accelerating in a given area.

When IJ arcing is discovered, train movements in the area should be investigated. If it is unknown when IJ arcing occurs, a greater effort in investigating overall train movements over a longer period may be required. A look at train locations and the train combinations at a given time may provide insight into the situations when IJ arcing occurs. This insight can lead to determining what mitigations are required to prevent future arcing events.

Video cameras can be a useful tool in investigating IJ arcing events (Ryabchik et al. 2020a). Now very durable and inexpensive, video cameras also have battery and storage capacity that allow long recording periods without extensive installations. Recording an IJ for a period can provide insight regarding when IJ arcing occurs and the magnitude of those events. The timing of IJ arcing combined with the movements of trains in the area can provide insight into the root causes of the IJ arcing and the required mitigations.

Many times, reviewing train schedules or having a single discussion with train dispatchers or transportation planners will yield useful information on train movements. Train control and train dispatching system logs that record train movements are another useful source of information.

Control Centers

Control center personnel and their records and logs can be a valuable source of information when investigating issues with wayside equipment. Unusual events that impact the operation of trains may be noted by control center personnel, but personnel may have no idea of the cause or impacts on the wayside equipment. When IJ arcing is found, those who manage or control the operations of the trains and oversee or operate the traction power system should be included in the investigation. Where IJ arcing is intermittent, or appears to be an isolated event, incident or trouble logs can provide valuable information that can lead to identifying when the event occurred.

Broken Rails and Electrical Arcing

No reports indicated broken rails resulting from sparking or arcing at the rail ends of IJs. However, some reports denoted rail defects initiated by electrical arcing but unrelated to IJ arcing. These defects included arcing at loose TPNR cable rail connections and ground-fault arcing between the running rails and the earth ground (see Figure 12). Reports were also found related to broken rails caused by improperly installed rail cable connections (NTSB 2005a). One paper investigates the possibility of rail defects that might result from IJ arcing; however, the work

provides only theoretical discussions on how the damage to rails from IJ arcing might lead to rail breaks and does not cite any broken rails that had occurred (Ryabchik et al. 2020b).

When rail breaks occur on an electrified railway, TPNR arcing between the faces of the broken rail may also take place. When a rail break occurs, the TPNR electrical path is broken; if the rail ends come into intermittent contact, arcing unrelated to the cause of the broken rail will occur. Arcing with a similar appearance to IJ arcing can occur at rail breaks or at rail joints that are improperly bonded (cables that electrically connect the rail ends). The cause of a broken rail that exhibits arcing damage that occurred after the rail has broken should not be confused with the cause of a rail defect initiated by electrical arcing (see Figure 13).

The type of rail damage that can occur from IJ arcing has a lot of similarities to improper rail welding or torch cutting of rail. The negative effect of improper welding or torch cutting of rails is well understood and addressed in most track maintenance standards [reference APTA Rail Transit Track Inspection and Maintenance Standards §10.1.6, FRA Track Safety Standards §213.122 (49CFR213.122), and Transport Canada Rules Respecting Track Safety, Subpart D, §V.g.].

When destructive arcing occurs, IJs and associated rails are commonly replaced because the damaged insulation interferes with the train control system, or excessive wheel impacts are caused by metal loss on the running surface of the rail. It is likely IJs suffering destructive levels of arcing are replaced before cracks or breaks in the rail can develop.

Rail ends at IJs that have experienced sparking or arcing damage should be carefully monitored if left in service. If monitored using ultrasonic testing, care should be taken to ensure that the poor rail surface conditions caused by the sparking or arcing do not impede the performance of the ultrasonic testing [reference FRA Track Safety Standards §213.240 (49CFR213.240)].