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Current collection characteristics and improvement methods of high-tension overhead catenary systems


Electrical Engineering in Japan, Vol. 123, No. 4, 1998

Translated from Denki Gakkai Ronbunshi, Vol. 117-D, No. 6, June 1997, pp. 704?711

Current Collection Characteristics and Improvement Methods of High-Tension Overhead Catenary Systems
MITSUO ABOSHI ISSEI NAKAI
JR West, Japan

Railway Technical Research Institute, Japan

HIROKAZU KINOSHITA
JR Shikoku, Japan

SUMMARY With increasing speeds on electric railways, overhead catenary systems on narrow-gauge lines have been improved by increasing messenger wire tension. However, the contact loss ratio of the pantograph is comparatively high in heavy-simple or feeder-messenger wire-type overhead catenary systems. These catenaries have higher tension of the messenger wire. In order to investigate the causes of contact loss and to work out effective improvement methods, laboratory and field tests have been carried out. From the results thereof, it is confirmed that the contact force fluctuation is influenced by the wave reflection factor at the hanger, and a hanger which has a spring mechanism is found to effectively improve it. It is expected that rubber damping hangers or friction damping hangers will reduce contact loss of the pantograph and wear of the contact wire. ?1998 Scripta Technica, Electr Eng Jpn, 123 (4): 67?76, 1998 Key words: Electric railway; current collection; overhead contact line; contact loss; heavy-simple catenary; feeder-messenger catenary. 1. Introduction Recently, higher speeds have been promoted in electrical railways in Japan. On narrow-gauge lines including those of the Japan Railways (JR) group, the maximum speed of commercial operation is 140 km/h now, and 160 km/h operation is expected in the near future. For highspeed operation in electric railways, reducing contact loss of the pantograph is one of the most important subjects. Contact loss causes power interruption and increases wear of contact strips and contact wires.

A simple catenary system which has a total tension of 19.6 kN (Fig. 1) has been used ordinarily for narrowgauge lines. As the uplift of this catenary is comparatively large, however, many accidents have occurred as trains run at higher speeds and the number of pantographs increases. Therefore, in high-speed or high-wind sections, the catenary has been improved to a heavy-simple catenary in which the tension of the messenger wire increases (Fig. 1). However, in this catenary system, the contact loss ratio of the pantograph is comparatively high, and some forms of this catenary are not applicable to commercial operation above 120 km/h [1].

Fig. 1. Example of high-tension overhead catenary system. CCC0424-7760/98/040067-10 ? 1998 Scripta Technica

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On the other hand, a feeder-messenger wire is used as a feeder cable and a messenger wire simultaneously in narrow tunnels. A feeder-messenger wire is generally designed so that the cross-sectional area is broad (the linear density is large) to satisfy the electrical capacity and the tension is strong to prevent excessive catenary dips. Excessive contact loss of the pantograph and severe wear of the contact wire occur in this catenary too. These are serious problems for maintenance of the overhead contact line. In the above-mentioned catenary, the tension of the messenger wire is larger than that of the contact wire. We call these catenary systems ?high-tension overhead catenary systems? (or ?high-tension catenaries?). In order to investigate the causes and to work out effective improvement methods, laboratory and field tests have been carried out [2?4]. This paper describes the relation between the reflection factor of the wave motion and the contact force fluctuation of the pantograph, and discusses improvement methods to reduce the contact loss ratio for a high-tension catenary. 2. Contact Loss Characteristics with High-Tension Catenary 2.1 Relation between contact force fluctuation and contact loss A pantograph is pressed to a contact wire with a stationary upward force (the sum of a static upward force and an aerodynamic upward force). The contact condition is stable, if the contact force between the pantograph and the contact wire is nearly equal to the stationary upward force. As shown in Fig. 2, the contact force fluctuates with the vibration of the pantograph in a span length period or a hanger space period, and also with the height change or unevenness of the contact wire. The pantograph loses contact with the contact wire when the contact force is 0. Because the mean of the contact force is nearly equal to the stationary contact force, it is considered that the contact loss is higher when the contact force fluctuation is larger. In this paper, the contact force fluctuation means the difference from the stationary contact force, and the standard deviation of the contact force is provided as an estimating parameter of the contact force fluctuation. The contact loss ratio (ratio of the contact loss time versus the total operation time) is used as an index of the estimated contact loss. 2.2 Contact loss ratio for high-tension catenary Figure 3 compares the contact loss ratios measured in a field test (Yosan line, 1993.3) [5]. These contact loss

Fig. 2. Illustration of contact force fluctuation.

ratios were measured by the current measuring method [6] to detect the current in the bus line between pantographs. The minimum length of the estimating sections is about 300 m. In Fig. 3, ?110 km/h? represents mean values in a speed range between 100 and 119 km/h, and ?125 km/h? a speed range between 120 and 130 km/h. Each catenary has the feature that the contact loss ratio is higher for later pantograph order, but the contact loss ratio for any high-tension catenary is higher than that for a simple catenary. The mean contact loss ratio of the following pantograph exceeds 5% under the heavy-simple

Fig. 3. Comparison of contact loss ratio (Yosan line).

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catenary at 125 km/h, and under the feeder-messenger catenary at 110 km/h. 2.3 Analysis of contact force fluctuation To analyze contact loss characteristics, it is effective to investigate the contact force fluctuation. As measuring methods of the contact force in a field test have not been developed, we analyze it by a computer simulation method [7] for pantograph-catenary dynamics. The catenary is replaced with multiple point masses, and the motions of the masses are related by simultaneous equations. A pantograph is represented by a mass-spring system. Figure 4 compares the contact force fluctuation for a heavy-simple catenary and a simple catenary. The conditions of the simulation are that the pantograph number is one, the stationary upward force is 54 N, the mass of the pantograph is 21 kg (one mass model), the span length is 50 m, the hanger space is 5 m, the train speed is 160 km/h, and the hanger cannot part from the messenger wire. For a simple catenary, the contact force fluctuation is comparatively large because of the vertical motion of the pantograph in a span period, and the contact force becomes small after passing a support point. On the other hand, under a heavy-simple catenary, the contact force fluctuation caused by the motion in a span period is comparatively small, but that in a hanger period is large (it is large at a hanger, and small at the center between hangers, and the differential is large). The contact force near the center between hangers under a heavy-simple catenary is smaller than that under a simple catenary (except immediately after passing a support point).

From simulation analyses, it is found that large contact force fluctuation in a hanger space period is the main factor for the contact loss of a high-tension catenary. 3. Contact Force Fluctuation Caused by Wave Motion 3.1 Reflection factor of wave motion at hanger In order to analyze the wave propagation characteristics of the contact wire at a hanger, we assume the model shown in Fig. 5, in which the contact wire is regarded as an infinite string, and the hanger does not part from the messenger wire. When the wave motion of the contact wire becomes incident to the hanger from the left-hand side, the wave motion of the contact wire and the messenger wire are written as follows: (1) (2) (3) (4) (5) (6) where rT, r M, TT, TM indicate the linear density and the tension of the contact wire and the messenger wire; A1, A3 are the amplitudes of the backward wave motion; B1, B2, B3 are those of the forward motion; w is the angular frequency of the wave motion; cT, cM are the wave propa-

Fig. 4. Comparison of contact force fluctuation (simulation).

Fig. 5. Model of contact wire and hanger.

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gation velocity of the contact wire and the messenger wire; and i is the imaginary unit. From the boundary condition of the displacement at the hanger, (7) (8) and from the boundary condition of the force at the hanger,

(18) (19) where ZT, ZM are called the mechanical impedances of the contact wire and messenger wire, and are defined as the ratio of the exciting force to the vibration velocity. In the case of an ordinary hanger with k = ?, D = 0, mM = 0, the reflection factor is rewritten as follows: (20)

(9)

(10) where mT, mM, k, D are the mass of the contact wire side, the mass of the messenger wire side, the spring constant, and the damping ratio of the hanger, respectively. Substituting Eqs. (1) to (6) into Eqs. (7) to (10), we obtain the ratios of the amplitude of the reflected wave, the transmitted wave, and the messenger transmitted wave to that of the incident wave as follows: (Reflection factor) (11) (Transmission factor) (12) (Messenger transmission factor) (13) where (14) (15) (16) (17)

On the condition that mT w << ZM (suppose that mT @ 0.2 kg, ZM @ 300 Ns / m, when w << 1500 rad/s), the reflection factor in Eq. (20) is rewritten as the following equation independent of the angular frequency: (21) When the mechanical impedance of the messenger wire is larger than that of the contact wire, the absolute value of the reflection factor becomes comparatively high. If the mechanical impedance of the messenger wire is extremely large, the reflection factor becomes nearly ?1. 3.2 Relation between reflection factor at hanger and contact force fluctuation Second, by using the computer simulation method, we analyze the relation between the reflection factor at a hanger and the contact force fluctuation. Figure 6 shows the standard deviation of the contact force with only the mechanical impedance of the messenger wire changed from that of a heavy-simple catenary. The linear density and the tension of the messenger wire are changed at the same ratio, and therefore the wave propagation velocity of the messenger wire is constant. The reflection factor is calculated from Eq. (21). There is a tendency for the contact force fluctuation to be larger when the absolute value of the reflection factor |R| is higher. It becomes very large when the reflection factor exceeds 0.5. 3.3 Contact force fluctuation caused by wave motion of contact wire The reason that the contact force fluctuation is larger for a catenary in which the reflection factor is higher is as follows. The wave motion of the contact wire is originally excited by a pantograph, propagates forward and backward,

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Table 1. Example of reflection factors

Fig. 6. Relation between reflection factor and contact force fluctuation. catenary have the feature that the mechanical impedance of the messenger wire is larger than that of the contact wire, and the reflection factor is higher than that of a simple catenary. Therefore, it is considered that the contact force fluctuation in a hanger space period is the main factor of contact loss. 3.5 Methods to reduce reflection factor at hanger In order to decrease the contact loss ratio for a hightension catenary, it is necessary to reduce the reflection factor at the hanger. As shown in Eq. (21), the improvement method is essentially to make the mechanical impedance of the messenger wire not too much larger than that of the contact wire. Second, hangers must be made elastic. We can rewrite Eqs. (11) and (14) as follows:

reflects at hangers, and repeats this process. Thus, the propagation of the wave motion involves great superposition. When the wave motion incident to the pantograph is expressed by (22) and the pantograph is regarded as a one-mass model, the contact force fluctuation is represented as follows (23)

The contact force fluctuation |FP| is proportional not only to the amplitude of the incident wave |B1|, but also to w on the condition that mw >> ZT is satisfied (assuming m @ 20 kg, ZT @ 300 Ns/m, when w >> 1500 rad/s). It is found that the contact force fluctuation |FP| is larger when the vertical velocity of the wave motion incident on the pantograph |wB1| is larger. The above simulation analyses prove that the contact force fluctuation is larger with a catenary in which the reflection factor at a hanger is higher. This is because the greater part of wave motion reflects at a hanger and becomes incident to the pantograph. 3.4 Reflection factor of high-tension catenary Table 1 shows an example of reflection factors at the hangers of typical high-tension catenaries [calculated by Eq. (21)]. A heavy-simple catenary and a feeder-messenger

(24)

(25)

Therefore, decreasing d, that is, decreasing mT and k, is effective in reducing the reflection factor. If we can ignore the first term of the denominator in Eq. (25) and D, the angular frequency at which the reflection factor becomes the smallest is as follows: (26)

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Fig. 8. Improvement of reflection factor. Fig. 7. Friction damping hanger and rubber damping hanger. 4.1 Current collection test equipment The current collection test equipment is composed of a vehicle driven by L.T.M., and an actual catenary and pantograph available for the experiment. The test line length is about 500 m, and the measurement of the current collection quality is carried out in the coasting section where the speed is approximately constant. In this running experiment, a PS26-type pantograph (damper attached) for high-speed operation in narrow-gauge lines was used. 4.2 Condition of running experiments In the case of a heavy-simple catenary, the experimental condition for the higher reflection factor is (1) the increase of the messenger wire tension, and those for the lower reflection factor are (2) the change of the contact wire and the messenger wire tension and (3) rubber damping hangers. In the case of a feeder-messenger catenary, the experimental conditions for the higher reflection factor are (1) double messenger wires and (2) fixed hangers, and those for the lower reflection factor are (3) increase of the contact wire tension, (4) rubber damping hangers, (5) friction damping hangers, and (6) short hanger space. The improvements on commercial lines must be relatively inexpensive, so the experimental conditions have taken this into account. Until now, we have assumed that hangers do not part from the messenger wire. But it may occur that the hanger parts from the messenger wire, and the wave reflection factor decreases momentarily when a pantograph passes. In these experiments, on commercial lines, the hangers are able to part from the messenger wire

We have developed a friction damping hanger [8] and a rubber damping hanger [9] as practical elastic hangers. The friction damping hanger is developed to have a lower spring constant. A coil spring is used and the spring constant is about 1.5 kN/m. On the other hand, the rubber damping hanger is developed as a simple and economical one. A piece of rubber is bonded with vulcanization at the top of the hanger. Chloroprene (CR) is adopted as the rubber material, taking into account its durability and temperature dependency. The spring constant of a rubber damping hanger, between about 52 and 60 kN/m, is higher than that of a friction damping hanger. Figure 8 shows the effect of reducing the reflection factor by using these damping hangers. A friction damping hanger is effective in reducing the reflection factor even in the lower frequency range [wr = 86.6 r ad/s ( f = 13.8 Hz) in Eq. (26)]. On the other hand, a rubber damping hanger is effective in the higher frequency range [wr = 524 rad/s ( f = 83.5 Hz)].

4. Running Experiments on Current Collection Test Equipment We carried out running experiments on current collection test equipment at the Railway Technical Research Institute, and confirmed the current collection quality and the improvement effect under the typical high-tension catenary.

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(not fixed) except for some special conditions. Hanger space reduction is the condition under which hangers most readily part from the messenger wire by reducing the axial force of the hanger. 4.3 Results of experiments Figure 9 shows results of an experiment with a heavysimple catenary (span length 50 m), and Fig. 10 shows those of a feeder-messenger catenary (span length 10 m). The values in parentheses indicate the wave reflection factor at a hanger, which is the mean of values at w = 62.8 rad/s ( f = 10 Hz) and w = 628 rad/s ( f = 100 Hz) in Eq. (11). Figure 11 shows the relation between the reflection factor and the mean contact loss ratio. The contact loss ratio tends to be higher when the reflection factor is larger. It becomes very large when the reflection factor exceeds 0.5. This inclination agrees approximately with the above-mentioned simulation analyses (Fig. 6). It is confirmed that using rubber damping hangers or adjusting the tension of the catenary is effective in reducing the reflection factor and the contact loss ratio. The contact loss ratio for a heavy-simple catenary is higher than that for a feeder-messenger catenary in the region where the reflection factor is higher. It is considered that a hanger used in a feeder-messenger catenary can easily part from the messenger wire when a pantograph passes.

Fig. 10. Result of experiment (feeder-messenger catenary).

When the tension of the contact wire increases, the decrease of the contact loss ratio is much greater than that with only a decrease of the reflection factor. It is considered that it involves a decrease of the contact force fluctuation caused by increasing the total tension of the catenary.

Fig. 9. Result of experiment (heavy-simple catenary).

Fig. 11. Relation between reflection factor and contact loss ratio.

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5. Field Test of Improvement Methods From the above-mentioned experimental results, it is confirmed that reducing the wave reflection factor at a hanger is an effective way to decrease the contact loss ratio under a high-tension catenary. Thus, the following improvements are considered to be effective and economical. (1) Use elastic hangers. (2) Revise the tension of the catenary. We applied some improvement methods to the commercial lines and confirmed the effect. 5.1 Field test on Yosan line Figure 12 shows the improvement effect by using friction damping hangers or rubber damping hangers [5]. The field test was carried out on the Yosan line (1993.3, 8000 series car). Rubber damping hangers are set along 300 m of a heavy-simple catenary, and friction damping hangers are set along 60 m of a feeder-messenger catenary (all hangers). In the case of an ordinary hanger, the contact loss ratio of the following pantograph is over 5% for a heavysimple catenary at 125 km/h or for a feeder-messenger catenary at 110 km/h. It is confirmed that rubber damping

hangers or friction damping hangers are able to considerably decrease the contact loss ratio, to 1 to 3%. 5.2 Field test on Kosei line Figure 13 shows the improvement effect obtained by using rubber damping hangers under a heavy-simple catenary (GT170 mm2, 11.8 kN) [5]. The field test was carried out on the Kosei line (1992.10, 681 series car). Rubber damping hangers were set along 325 m of a heavysimple catenary (all hangers). The contact loss ratio was measured on the rubber damping hanger section and on the ordinary hanger section in the same drum. In the case of ordinary hangers, the contact loss ratio was over 10% (the average of each pantograph) at a speed of 160 km/h, and rubber damping hangers are able to decrease it to about 3%. 5.3 Field test on Chuo-East line Figure 14 shows the improvement effect obtained by revising the tension of the contact wire and the messenger wire of a heavy-simple catenary. The field test was carried out on the Chuo-East line (1993.10, E351 series car) [3]. When the tension of the contact wire increases to 14.7 kN with the same total tension, the contact loss ratio decreases to under 1.5% from 3 to 8% [1] at 130 km/h. In addition, by using the rubber damping hangers, the contact loss ratio decreases to under 0.5% at 130 km/h.

Fig. 12. Effect of reducing contact loss ratio (Yosan line).

Fig. 13. Effect of reducing contact loss ratio (Kosei line).

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wave motion at a hanger is higher, and that a high reflection factor is the main factor of contact loss for a high-tension catenary. (2) Using hangers with a spring mechanism or adjusting the tension of the catenary is effective in reducing the reflection factor and to decreasing the contact loss ratio.

Acknowledgments The authors wish to thank staff members of JR-East, JR-West, and JR-Shikoku for their great help in the field tests, and also Professor Kazuo Yoshida of Keio-Gijyuku University for support and help. REFERENCES Fig. 14. Effect of reducing contact loss ratio (Chuo-East line). 1. Yasoura. IEEJ, NC?90, 8-153 (1990). 2. M. Aboshi and N. Mifune. IEEJ, TER-93-37, pp. 51?60 (1993). 3. M. Aboshi and I. Nakai. IEEJ, TER-94-38, pp. 57?66 (1994). 4. I. Nakai and M. Aboshi. IEEJ, TER-95-4, pp. 27?36 (1995). 5. I. Nakai, M. Aboshi, and H. Kinoshita. IEEJ, JIASC?94, pp. 649?650. 6. R.T.R.I. Characteristics of Overhead Contact Line and Pantograph. Kenyusha, pp. 226?230 (1993). 7. Y. Fujii and K. Manabe. Computers in Railways III (1992). 8. M. Aboshi et al. IEEJ, TER-94-13, pp. 57?66 (1994). 9. M. Aboshi et al. IEEJ, NC?94, 8-207?208 (1994).

6. Conclusions From the above-mentioned simulation analyses, running experiments, and field tests, the conclusions regarding the current collection quality and the improvement of hightension catenaries are as follows. (1) It is confirmed that the contact force fluctuation is larger with a catenary in which the reflection factor of the

AUTHORS

Mitsuo Aboshi (member) graduated from Kyoto University in 1979 and then joined Japanese National Railways, where he worked on planning, construction, and maintenance of overhead equipment. He moved to the Railway Technical Research Institute in 1987, and conducted research on current collection dynamics. He is currently Chief Researcher, Fundamental Research Division, Railway Technical Research Institute.

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AUTHORS (continued) (from left to right)

Issei Nakai (member) graduated from Tokyo University in 1990. He joined the Railway Technical Research Institute in 1992, performing research on current collection dynamics. He is currently Assistant Manager, Seto-Uchi Local Railway Division, West Japan Railway Company. Hirokazu Kinoshita (nonmember) graduated from Yawatahama Technical High School in 1972 and then joined Japanese National Railways, where he worked on planning, construction, and maintenance of overhead equipment and power supply. He is currently Assistant Manager, Takamatu Electric Division, Shikoku Railway Company.

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