## 4 Results
### Second Case  
Healthy Condition When the Connection of the Railway Tracks with the Impedance Bond Is Made through Two Steel Cables with a Section of 78 mm\({}^{2}\) with PVC Insulation  
In addition, the case of the connection between an impedance bond terminal and railway track with two steel ropes was analyzed. The values of the contact resistances to the contact area are given in Table 3. Figure 8 shows the time evolution of the temperature after the different currents passing the contact area. Thus, the following temperature values were obtained: for 100 A, a 34.8 \({}^{\circ}\)C value; for 150 A, a 46.1 \({}^{\circ}\)C temperature value; and for 200 A, a temperature value of 61.2 \({}^{\circ}\)C.  
Analyzing the contact area temperature, corresponding the first case (at 3600 s and 100 A currents passed) with the second case, it can be observed that 32.3 \({}^{\circ}\)C value is closed with 34.8 \({}^{\circ}\)C value, the difference being smallest than 2.5 \({}^{\circ}\)C. Although the contact resistance in the first case is higher than in the second case, the overheating is closed; this is due to the increase of the heat transfer surface in the second case. Since the thermal stresses in the case of contact with the copper rope are smaller, these connections should be made from this material. However, for economic reasons (not only robberies, vandalism), in operation, the connections with two steel cables are used. Figure 8: Temperature variation from the contact area by impedance bond and two steel conductors at different currents (100 A, 150 A, 200 A). Figure 7: Temperature variation from the contact area by impedance bond and one copper conductor at different currents (100 A, 150 A, 200 A). Third Case--Faulty Condition When Connecting the Railway Tracks with the Impedance Bond Is Made through One Steel Cable with a Section of 78 mm\({}^{2}\) with PVC Insulation  
This fault may occur when a steel cable between the impedance bond terminal and the railway track is broken because of overheating, railway accidents, etc. Figure 9 shows the temperature variation in the terminal contact area of the impedance bond when it is connected by a steel rope to the railway track, at the same values of the currents as the other cases. The temperature reaches to 52.5 \({}^{\circ}\)C, for a current of 100 A, 78.5 \({}^{\circ}\)C for 150 A, and 124.4 \({}^{\circ}\)C for 200 A. Moreover, the temperature in the terminal contact area has different evolutions due to the current values; the contact resistances, having almost the same values, do not influence the measurements. By comparing the obtained results with the first case at the same transited current, the temperature in the contact area is higher (for example, at 100 A, it has 52.5 \({}^{\circ}\)C \(>\) 32.3 \({}^{\circ}\)C). This big difference, 20.2 \({}^{\circ}\)C, is because the resistivity of the steel is higher than the copper resistivity, which will cause higher Joule losses on the steel rope. In addition, Figure 9 shows that, with the increase of the current over a certain value, the temperatures will exceed the allowable limits given by the impedance bonds manufacturer (105 \({}^{\circ}\)C on the terminal contact). At 200 A, with a single connecting rope, the values of the temperatures in the contact area exceed the allowable value, after approximately 1545 s. This fact can lead to thermal overloading of the impedance bond semi-windings from the ends of the circulation sector on which the abnormal situation appeared, respectively, to the blocking of the control circuit in that circulation sector. In this case, a maintenance activity to complete the connection between impedance bond and railway tracks with another steel connection ropes are necessary. Moreover, a thermographic image was performed, when the connection of the railway tracks with the impedance bond was made through a copper cable (healthy condition) and the connection with one steel cable (faulty condition).