Diagnosis of Overhead Contact Line based on Contact Force. Takahiro FUKUTANI Current Collection Laboratory, Power Supply Division

Transcription

1 PAPER Diagnosis of Overhead Contact Line based on Contact Force Shunichi KUSUMI Contact Line Structures Laboratory, Takahiro FUKUTANI Current Collection Laboratory, Power Supply Division Kazuyoshi NEZU Current Collection Laboratory, Large contact force fluctuations between contact wires and pantographs cause unstable current collection conditions and so it is important to measure and estimate the contact force to obtain a better knowledge of current collection quality. waveforms are affected by the condition of equipment used on overhead contact lines, so it is to be expected that the contact force waveform represents the state of repair of an overhead contact line. This paper describes contact force waveform characteristics against the static height of Shinkansen contact wires and their application in overhead line diagnosis. Keywords: contact force, overhead line diagnosis, contact loss, contact wire static height, overlap structure, aerodynamic upward force 1. Introduction Large contact force fluctuations between contact wires and pantographs cause unstable current collection conditions. When the contact force nears (N), it is difficult to maintain the contact between the contact wire and the pantograph, and an arc is generated, accelerating the wear of sliding parts. On the other hand, when the contact force is too great, mechanical damage is caused to those sliding parts. Therefore, it is important to measure and estimate the contact force to obtain a better knowledge of current collection quality. Contact force waveforms are affected by a number of factors relating to the conditions in which the overhead contact lines are installed and so it is presumed that the contact force waveform can be used to diagnose the state of overhead contact lines. This paper presents contact force waveform characteristics and their application in overhead line diagnosis. 2. measurement method and accuracy improvement 2.1 Measurement method We would like to briefly explain the principles of contact force measurement. The pantograph can be divided into two parts, part 1 being the part on which the contact force acts, as shown in Fig.1. The equilibrium of the forces acting on the pantograph head can be expressed by Equation (1), Inertia force : f ine Part 1 Part 2 : f c Aerodynamic upward force : f L Panhead Inner force : f b,i (i=1,2,..,m) Articulated frame Static upward force Fig. 1 Equilibrium of forces acting on pantograph fc = fine + fb + f L (1) f c = applied to pantograph head f ine = Pantograph head inertia force f b = Force acting on pantograph head from pantograph arm f L = Aerodynamic upward force acting on pantograph head We will be able to obtain the contact force, therefore, if we can measure the inertia force, internal force and the aerodynamic upward force of the pantograph head. At higher frequencies, the pantograph head in part 1 cannot be regarded as a rigid model and the elastic vibration dominates. Then, the inertia force can be obtained accurately by a weighted summation of acceleration values measured at multiple points on part 1. Figure 2 shows the low noise-type pantograph that is used for Shinkansen running tests. In this case, four accelerometers are mounted on the pantograph head and the internal force is obtained by measuring the strain on the pan-spring. On the other hand, it is difficult to measure directly the aerodynamic upward force acting on part 1. For some types of pantographs, we have developed an aerodynamic upward force measurement method based on contact wire deviation measurements Inertia force Panhead Inner force Panhead Support Spring Accelerometer Strain gauge (on the spring) Articulated frame Fig. 2 Measurement devices installed on low noise-type pantograph QR of RTRI, Vol. 47, No. 1, Feb

2 1). However, this method cannot be applied to the pantograph in Fig. 2. The aerodynamic upward force is proportional to the square of the relative flow velocity against the pantograph. Therefore, the aerodynamic upward force can be estimated by the running speed based on the relationship between the aerodynamic upward force and the flow velocity on the running test. With the exception of the aerodynamic upward force in Equation (1), forces were measured during a running test. 2.2 compensation based on aerodynamic upward force Aerodynamic upward force measurement method Figure 3 shows the aerodynamic upward force measurement method. The pantograph is lowered to a position separated from the contact wire and the string is connected to a load cell on the pantograph's underframe. The load cell output indicates the pantograph's overall aerodynamic upward force. In order to obtain the average force, the inertia force can be ignored. Therefore, the contact force f c can be expressed as = f b + f L (2) f b is defined as the internal force, as shown in Fig. 2. Thus, the aerodynamic upward force of the pantograph head f L can be expressed as f = f (3) L Load cell b String Upward force(n) Fig. 4 Aerodynamic upward force Measurement result Panhead upward force Load cell (running test) Load cell (wind tunnel test) Panhead upward force Overall upward force Velocity (km/h) Inertia force + inner force Static upward force + upward force (Wind tunnel test) Inertia force + inner force Velocity (km/h) Fig. 5 Mean contact force measurement result pantograph frame has a negative aerodynamic upward force. The velocity characteristic of the mean contact force that was corrected by the pantograph head's aerodynamic upward force approximately matches the aerodynamic upward force characteristic obtained in wind tunnel tests added to the static upward force. This can prove that correcting the aerodynamic upward force provides sufficient accuracy. Fig. 3 Aerodynamic force measurement method Aerodynamic upward force and mean contact force measurement results The aerodynamic upward force is obtained as a negative value of the internal force, as shown in Eq. (3). Figure 4 shows the pantograph head's aerodynamic upward force measurement result. The load cell running test result proved that the overall pantograph aerodynamic upward force approximately matches the wind tunnel test result 2), and the aerodynamic upward force acting on the pantograph head is approximately proportional to the square of the running speed. The contact force is obtained from the sum of the measured force (the internal force and the inertia force) and the pantograph head's aerodynamic upward force corresponding to the train speed. Figure 5 shows the velocity characteristics of the mean contact force. The inertia force plus the internal force, excluding the aerodynamic upward force, declines with running speed. This force includes the aerodynamic upward force of the pantograph frame, therefore the 3. waveform characteristics 3.1 and catenary structure Normal section Contact wires come into direct contact with pantographs, therefore the height condition of a contact wire significantly influences current collection performance. In order to gain an understanding of the relationship between the contact force and contact wire height, we measured the former on board the train and the static height together with contact wire wear on a maintenance wagon. Figure 6 shows these measurement waveforms. The contact force, pantograph height and contact loss in terms of pantograph current were measured by readings taken from the first pantograph at a speed of 28 km/h. Figure 7 shows the result of frequency analysis of the data from the pantograph and the contact wire (contact wire wear, pole position and static height). This particular contact wire had sag and the pantograph height fluctuated similar to the contact wire's static height and the outstanding spatial frequency in the contact force 4 QR of RTRI, Vol. 47, No. 1, Feb. 26

3 Overlap section Contact wire static height Pantograph height Pole Overlap section 15.5mm 15.mm 1mm 1N N Contact loss Time(s) Fig. 6 Contact wire condition and contact force waveform (28km/h) PSD(N2/Hz, mm 2 /Hz, 1/Hz) PSD(mm 2 /Hz) Fig. 7 1.E+3 1.E+2 1.E+1 1.E+ 1.E-1 1.E-2 1.E-3 1.E-4 1.E+4 1.E+3 1.E+2 1.E+1 1.E+ 1.E-1 1.E-2 1.E-3 1.E-4 1.E-5 1.E-6 Pantograph Height Contact loss Wave number (1/m) (1) Pantograph data Contact wire static height Wave number (1/m) (2) Contact wire data Frequency analysis of each set of measurement data within the span cycle (.2-.3(1/m)). Fluctuations in contact force included a dropper and hanger spacing cycles, and the contact loss also included similar fluctuation components. On the other hand, although the wear spectrum had span spacing and hanger spacing cycle components, it was not possible to confirm the dropper space component. When the low frequency, up-anddown motion such as that found in the span spacing cycle is analyzed, the pantograph can be expressed as a model of a mass (pantograph head and pantograph frame) and upward force. In this case, the contact force F can be expressed as 2 = d y 2 F P m dt (4) y = Up-and-down displacement of pantograph m = Mass of pantograph head and frame P = Static upward force In the low-frequency domain, the contact force is increased when the acceleration is negative, and the contact force is decreased when the acceleration is positive. To confirm this relation, we compared the contact force with the acceleration. The acceleration can be calculated, as shown in Eq.5, yi n 2 yi+ yi+ n a = ( n x) 2 (5) y i = Sample data of i number of pantograph height n = Data space for calculation x= Sampling interval. To observe the contact wire fluctuation height in the span cycle, the data space defines the time interval (n x=.64s) that corresponds to a hanger space of 5m. Figure 8 shows the relationship between pantograph acceleration and contact force at support points receiving a large contact force, and Fig. 9 shows the relationship between pantograph acceleration and the curvature of the static contact wire height profile using Eq. (5): Pantograph acceleration 1-3 (m/s 2 ) Fig. 8 Pantograph acceleration and contact force -8 QR of RTRI, Vol. 47, No. 1, Feb

4 Curvature of static contact wire height profile 1-3 (1/m) Fig. 9 Pantograph acceleration and contact wire curvature n x=5m. From these figures, it can be seen that the negative higher acceleration makes the contact force large, and that the acceleration has a correlation with the contact wire's static height. These mean that the contact force is greater at places with greater curvature of static contact wire height profiles. The location of a greater negative curvature in the contact wire height profile denotes the location the contact wire height profile shape is convex upward, as shown in Fig. 6, and the contact wire height profile shape becomes sharp. This is caused by excessive sag or pulling up due to a metal fitting Overlap section Pantograph acceleration 1-3 (m/s 2 ) At overlap sections, the contact force increases more than 27N and local wear also occurs, as shown in Fig. 6. We know how overlap structure performance influences local contact wire wear from past study 3). Figure 1 shows the classification of the overlap structure. To confirm the relationship between the contact force and the overlap structure when the pantograph passes an overlap section, we compared the structure greater than normal contact force occurred with that normal contact force occurred. Figure 11(1) shows an example of the overlap structure greater contact force occurred. This figure corresponds to the right side overlap section in Fig. 6, local wear occuring on the B line. This structure is equivalent to Fig. 1(1). On the other hand, Fig. 11(2) shows an example of the overlap structure normal contact force occurred. This structure is equivalent to Fig. 1(3). There is wear in the hanger space cycle on the contact wire, however there is no local wear at the junction point, as shown in Fig. 11(2). Figure 12 shows the contact force at 28km/h and 32km/h at the overlap sections shown in Fig. 11. The contact force reached 36N at the overlap section shown in Fig. 1(1) when the running speed increased to 32km/ Train A line A line A line (1) (2) (3) Faulty structure Good structure Fig. 1 Classification of overlap structure -8 Fig Overlap section structure and contact wire wear Residualdiameter (mm) Pole A line Local wear Train Contact wire static height Distance (m) Distance (m) Fig. 12 Comparison of contact force by overlap structure h from 28km/h. The contact force is 2N at the overlap section in Fig. 11(2) at 32km/h, even smaller than that for Fig. 11(1) at 28km/h. If the overlap structure has a good structure, it can maintain good contact performance. 3.2 and contact loss 2mm (1) Overlap structure greater contact force occurs Residualdiameter (mm) Pole A line Train Contact wire static height 2mm (2) Overlap structure normal contact force occurs Overlap at Fig. 11(1) Overlap at Fig. 11(2) 28km/h 32km/h Contact loss is a phenomenon of the contact force (N), therefore we investigated the relationship between them. Contact loss is measured by the pantograph current data that clearly indicates the mechanical contact status of the pantograph with the contact wire. Figure 13 shows the contact force frequency distribution for cases the contact loss is % and 28%. 42 QR of RTRI, Vol. 47, No. 1, Feb. 26

5 Relative frequency Relative frequency Fm-3s =5.8N Fm-3s=-129.3N Fm=52.5N (1) Contact loss ratio=% Fm=56.6N s=15.6n Fm+3s=99.2N s=62.n (2) Contact loss ratio=28.2% Relative frequency Relative frequency Fm+3s=242.6N Fig. 13 frequency distribution The probability density functions calculated by the mean values and standard deviations are also shown. In the area contact loss occurred, the minimum contact force had a negative value because of the low-pass filter data processing, however the contact force distribution almost matched that of normal distribution in cases both with or without contact loss. When Fm-3s is positive (Fm denotes the mean contact force and s the standard deviation), it can be judged that the contact loss almost doesn't occur because over 99.85% of the contact force is positive. On the other hand, if Fm-3s has a negative value, it can be judged that the contact loss occurs because over.15% of the contact force is negative. Thus, we studied the relationship between Fm-3s of the contact force and contact loss. We were able to observe a Contact loss ratio(%) F m 3s (N) -15 Fig. 14 Relationship between Fm-3σ and contact loss ratio good correlation, as shown in Fig.14. In order to reduce the contact loss ratio, Fm-3s has to be decreased by decreasing s because Fm cannot be decreased as it is decided by the pantograph type. The mean contact condition in the measurement area can be expressed by the contact loss ratio. Consequently, if the contact force standard deviation is calculated, we can estimate the contact condition including the contact loss in the measurement area. 3.3 and contact wire strain It is possible that strain in excess of the criterion value occurs at the contact wire when the pantograph runs at speeds over 3km/h 4). If such a strain occurs repeatedly with every passing pantograph, it is possible that the contact wire will break due to fatigue. However, it is not easy to measure contact wire strain at high voltages, therefore it can be measured only at a few points To solve this problem, we observed the relationship between the contact force and contact wire strain. If the overhead contact line is defined as a tensioned elastic beam model, the strain, when the constant force F runs under the model, can be expressed as F EI 1 ε = 2ZE T 1 ( V/ c) 2 (6) EI = Contact wire rigidity Z = Contact wire section modules T = Contact wire tension c = Contact wire wave propagation velocity V = Running speed This equation expresses that the strain of contact wire is proportional to the contact force and is inversely proportional to 1 ( V/ c ) 2. In order to confirm this, we measured the contact wire strain together with the contact force. Figure 15 shows the relationship between the contact force and the strain during the running test. The theoretical value was calculated using Eq. (6) and the speed used for the theoretical value was that on the running test. This figure shows that the contact force and contact wire strain have a good correlation. As Contact wire strain km/h Measured value (28-34km/h) Theoretical value 285km/h Fig. 15 Relationship between contact force and contact wire strain QR of RTRI, Vol. 47, No. 1, Feb

6 shown above, contact force can be used to estimate the strain along all contact wire sections. Therefore the contact force should be able to detect locations of greater than normal contact wire strain. 4. Prospects for contact force-based overhead line diagnosis As described above, contact force amplitude is related to the profile condition of a contact wire in the span cycle or the contact wire strain, and the contact force deviation is proportional to the contact loss. Therefore, the profile condition of an overhead contact line could be estimated on board the train using contact force or pantograph height data. Based on contact wire profile condition diagnosis, the static height of a contact wire can be controlled so as to maintain the contact force at below criterion values. Thus, it is important for overhead contact line diagnosis to estimate the contact force, and then we have studied a contact force estimation method. (1) amplitude It is known that contact wire strain is greatest at those places high contact force and local contact wire wear tend to occur. The curvature of the pantograph height profiles and the contact wire static height profiles are larger at these places. However, the quantitative relationship between the contact force and the local contact wire wear or the appropriate curvature of the contact wire static height profile has not been clarified yet. Therefore we have estimated the maximum contact force based on its relationship with the contact wire strain. As a calculation method for the contact wire strain criterion, an estimation method based on the contact wire wear has been proposed. It was reported in reference 5) that the criterion will be if the contact wire wear ratio is.5mm/1 pantographs. Consequently, when the contact wire strain criterion value on the diagnosis is assumed to be and the maximum speed of commercial trains is assumed to be 34km/h, the contact force is evaluated as 34N against the strain criterion value from Fig.15. Therefore, this value would be the contact force criterion. However, if an inspection car that measures contact force were running at 285km/h, the contact force would be evaluated as 45N using Fig. 15. Inspection cars, however, don't always run at the same speed. Thus, the running speed in Eq. (6) was adjusted and then the diagnosis carried out. The place the strain exceeds the criterion value on the diagnosis may be the place greater contact force occurs and, as described at 3.1.1, a high curvature of contact wire height profile is presumed. To confirm this condition, it is necessary to include in the investigation the acceleration of the pantograph span cycle, and if it were high, the diagnosis system would indicate the necessity to check the contact wire height profile condition. On the other hand, we think that the contact force criterion value at the overlap section should be decided from the perspective of contact wire wear. It was reported in reference 6) that there is a correlation between contact force and contact wire wear. However, since the relationship of the running speed and the wear has not been clarified yet, it is necessary to conduct further studies into the relationship between the contact force and contact wire wear. (2) deviation According to reference 7), the appropriate contact loss ratio criterion value is 5% in the case of one pantograph running. Thus, Fm-3s is evaluated as -25N by Fig.14 when the contact loss ratio is 5%. When Fm is 65N, s is evaluated as 27N. There was only one section s was below this value at a running speed of 28km/h. The contact wire used on this section was newly developed PHC contact wire (13mm 2 ) that has an average curvature of contact wire height profile of (1/m), which is smaller than that at other places, for example (1/m). The contact loss ratio 5% is the value in the case of one pantograph running. However, in the case of two pantographs with a bus bar, since the contact loss arc is negligible, a contact loss ratio of about 3% can be permitted, in which case s is 7N. However, since this is diagnosed from the contact force standard deviation value, it is necessary to correct the speed. fluctuations during high-speed running are governed by the contact wire wave propagation in hanger spaces. The contact force from this wave propagation can be expressed using Eq. (7) 8). F wv 2ρgL Zp Z h p ( 1+ β) β = γ R π Z + Z Z + Z 1 β t p ω= ω t p ω= ωwv c ( 1 + β) β c ω = 2πβ, ωwv = 2π L 1 β L h ρ = Contact wire linear density g = Gravity acceleration L h = Hanger space γ R = Wave reflection coefficient Z p, Z t = Mechanical impedance of pantograph and contact wire β = Nondimensional velocity (V/c). As shown in this equation, the contact force fluctuation is proportional to (1+β)β/(1-β). Therefore, it would be possible to perform the speed correction by this relationship when the train runs at high speed and the contact force fluctuation in the hanger space is clear. However, when outstanding fluctuations occur in places other than hanger spaces, for example in span spaces or at localized places, this speed correction cannot be made. This will form the subject of future investigations. 5. Conclusion We have confirmed that contact force amplitude has a correlation with the contact wire height profile condition and contact wire stress, and that there is a good correlation between contact force fluctuation and the contact loss ratio. In addition, we introduced the application of this relationship for the purpose of overhead line diagnosis. The diagnosis of overhead contact line conditions and repair of abnormalities is very important for maintaining stable current collecting conditions. We intend to make further progress with research into this diagnosis method toward its operational use. h (7) 44 QR of RTRI, Vol. 47, No. 1, Feb. 26

7 References 1) Kusumi, S., et al., Measurement Method of Contact Force and Overhead Contact Line Diagnosis, Railway Engineering, London, England, July 6-7, 24. 2) Kusumi, S., et al., Characteristics of Contact Force Waveforms and Application to Diagnosis of Overhead Line, RTRI Report, Vol.19, No.7, pp.17-22, 25.7 (in Japanese) 3) Shimizu, M., et al., Improvement of Structure of Contact Wire on Overlap Sections of Shinkansen, Quarterly Report of RTRI, Vol.41, No.4, pp , ) Iwainaka, A., et al., Current Collecting Characteristics of Shinkansen Run at the Speed above 3 km/ h, Japan Industry Applications Society Conference, 3-23, pp , 24.8 (in Japanese) 5) Yamashita, C., et al., Measurement Method of Fatigue Life of Contact Wire with Concerning Wear, The Papers of Technical Meeting on Transportation and Electric Railway, IEE Japan, TER-5-15, pp.7-12, ) Terada. Y, et al., Diagnosis of Contact Line Overlap Composition by Contact Force, RTRI Report, Vol.16, No.6, pp.21-26, 22.6 (in Japanese). 7) Fujii. Y, et al., Investigation of allowable contactloss ratio related to contact strip wear, J-Rail2, No.149, pp , ) Aboshi. M, et al., Contact Force Fluctuation between Catenary and Pantograph, RTRI Report, Vol.13, No.7, pp.7-12, QR of RTRI, Vol. 47, No. 1, Feb