# Cognitive Principles for Remote Condition Monitoring Applied to a Rail Pantograph System
## 2 Background  
### Pantograph System  
A pantograph is the part of an electric tram or train that connects the vehicle to the catenary system (primarily consisting of a catenary wire and a contact wire), supplying the vehicle with the current it needs for power. The part of the pantograph that touches the catenary is known as the contact strip. This strip of graphite acts as both a conductor and as a lubricant. For the train to have a steady power supply, the surfaces of the strip and contact wire need to be smooth enough to slide across one another without jumping or snagging. A number of factors can affect pantograph performance. This can include the speed of the train, with a high-speed system being more demanding on the catenary-pantograph system than an urban or metro system. Weather can be a factor, including wind (which can impact contact forces) or rain and snow (which can impact the connectivity between pantograph and catenary). In addition, the general state of wear to either the pantograph, specifically to the contact strip or more generally to the mechanical operation of the pantograph, or to the catenary, can all have an impact on performance. Some of the common failure modes of the pantograph/catenary system identified in the literature [20; 21] are:* Pantograph aerodynamics are disturbed or set incorrectly
* Worn pantograph contact strip
* Pantograph geometry set incorrectly
* Incorrect contact wire height
* Catastrophic failure of pantograph or catenary system (often caused by other failure modes)
* Failure or displacement of droppers (often causing damage through contact with a pantograph)
* Uneven contact wire wear at discontinuity
* Formation of ice coating on contact wire (only an issue in certain seasons and/or climates). Issues with pantograph performance range from poorer conductivity through to the contact strip catching on the contact wire, tearing the entire catenary system down. This is very costly in terms of money and time. To prevent this, it is essential to monitor the pantograph-catenary interaction, analysing any unusual results. Furthermore, general monitoring of pantograph system behaviour can encourage both predictive maintenance and more cost-effective scheduling of component replacement for either the pantograph or the catenary. There are several metrics that can be used to indicate the wear of a pantograph contact strip, which include:  
- _Lateral Acceleration of the Contact Wire_: As a result of the side-to-side motion of the contact point, any inconsistencies or irregularities on the contact strip could 'catch' on the contact wire, exciting it laterally. The values expected for a pantograph in good condition range from 3-5 m/s\({}^{2}\), but for a worn or damaged contact strip these values tend to exceed 10 m/s\({}^{2}\)[22]. It is recommended that acceleration be measured using optical accelerometers that are attached to the contact wire and oriented perpendicular to the direction of the tracks. The use of optical transducers is recommended because they do not suffer from electrical interference created by the pantograph-catenary interaction. - _Temperature_: If the temperature of a pantograph contact strip exceeds what is expected (based on an estimation using a complex fuzzy system [23]), then a fault in the pantograph contact area is likely. When using temperature as a wear indicator, a good method for measurement of the contact strip is to use a thermal camera along with image processing techniques. This allows the whole of the contact strip to be monitored, while recording the point of maximum temperature as it moves across the length of the strip. - _Shape of the Contact Strip_: In order to transfer current from the catenary to the vehicle, the contact plate needs to be touching the contact wire. Over time, the friction from this contact causes a number of defects that can be visually identified, the most common of these being over-abrasion, partial abrasion, chipping, and groove-shaped abrasion.