# Cognitive Principles for Remote Condition Monitoring Applied to a Rail Pantograph System
## 2 Background
### Pantograph System
Groove-shaped abrasion is considered particularly dangerous, as if the contact wire catches in the groove, it could tear the entire catenary system down. Visually, it is easy to identify these defects during an in-person inspection. However, it can be more difficult to spot these through video. In order to identify these remotely, a number of deep learning algorithms have been developed [24; 25]. These algorithms use a convolutional neural network (CNN) to identify a pantograph from an image and determine which defect category the image should be classified as. However, carrying out maintenance activity requires more than just simply categorizing the defect. In order to have a quantitative representation of the defect, image processing methods can be used. Most image processing starts with some form of edge detection algorithm. The most effective for use on the pantograph-catenary [24; 26] uses a multi-stage algorithm to intensify and suppress certain pixels, leaving just the edges. The method described in [24] gives an estimate of wear depth by first picking out the required edges using the Hough transformation, an image processing method for identifying complex patterns in images [27]. These selected edges are then smoothed to remove any noise before the distance between the top and bottom edges is calculated. - _Position of Contact with Wire_: Due to the stagger (zig-zag path) of the contact wire, the point of contact between the pantograph and catenary should continuously slide across the contact strip from one side to the other [28] (see Figure 1). However, the contact strip of a worn pantograph is neither perfectly flat nor smooth. The wire will always move across the pantograph in the direction of least resistance; due to this, the contact position plot for a worn contact strip (see Figure 2) does not show the same uniform, side-to-side motion as that of the healthy pantograph. It is possible to determine the contact position using the dynamic response of the pantograph [29]; however, this requires the integration of accelerometers and strain gauges into the panhead. Another solution is to use some form of edge detection algorithm, to first detect the pantograph and overhead line, and then use an algorithm like that proposed in [28] to scan the video frame by frame, locating and saving the contact point for each. - _Arcing_: Arcing occurs when the pantograph loses contact with the contact wire, forcing the current to travel through the air, resulting in a visible flash, high temperatures and electrical interference [21; 23]. Although the presence of arcing is not necessarily a direct wear indicator, it is an unpredictable and inevitable phenomenon that can cause  
Figure 1: Path of wire on contact strip in good condition (adapted from [28]). Figure 2: Path of wire on contact strip in worn condition (adapted from [28]). significant damage to both the contact strip [21] and the catenary [30], as well as other railway equipment. For this reason, the detection of arcing is essential to any pantograph monitoring system.