Characteristics of Contact Force Waveforms and Their Application to Diagnosis of Overhead
Contact Line
1
1
Shunichi Kusumi , Takahiro Fukutani , Kazuyoshi Nezu
1
1
Railway Technical Research Institute, Tokyo, Japan
Abstract
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. Contact force 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 an
overhead contact line. This paper describes contact force waveform characteristics against the static
height of Shinkansen contact wires and their application in overhead contact line diagnosis.
1. Introduction
Large contact force fluctuations between contact wires and pantographs cause unstable current collection
conditions. When the contact force nears 0(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 contact line diagnosis.
2. Contact force measurement method
We would like to briefly explain the principles of contact force measurement. Figure 1 shows the low
noise-type pantograph that is used for Shinkansen running tests. The equilibrium of the forces acting on
the pantograph head can be expressed by Equation (1), as shown in Figure 1,
fc = fine + fb + fL
(1)
where
fc = Contact force applied to pantograph head
fine = Pantograph head inertia force
fb = Force acting on pantograph head from pantograph arm
fL = 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
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 the
pantograph head. 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. This sensor equipped pantograph is
enabling effective measurement of frequency up to 40 Hz.
On the other hand, it is difficult to measure directly the aerodynamic upward force acting on the
pantograph head. 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 or the wind tunnel test. With the exception of the aerodynamic upward force in Equation
(1), forces were measured during a running test. Figure 2 shows the pantograph head’s aerodynamic
upward force measurement result. 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.
Inertia force
Contact force
Panhead upward force
Overall upward force Running test)
Overall upward force Wind tunnel test)
80
Pantograph head
Accelerometer
Internal force
Spring
Strain gauge
(on the spring)
Figure 1: Measurement devices installed on low
noise-type pantograph
60
Upward force(N)
Aerodynamic
upward force
40
Panhead upard force
20
0
Overall upward force
-20
-40
0
50
100
150
200
Velocity (km/h)
250
300
Figure 2: Aerodynamic upward force
measurement result
3. Contact force waveform characteristics
3.1 Contact force and catenary structure
3.1.1 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 contact force on board
the train and the static height together with contact wire wear on a maintenance wagon. Figure 3 shows
these measurement waveforms. The contact force, pantograph height and contact loss in terms of
pantograph current were measured by the first pantograph at a speed of 280 km/h. Figure 4 shows the
result of frequency analysis of the data from the pantograph and the contact wire. This contact wire has
sag and the pantograph height fluctuates similarly with the static height of contact wire and the
outstanding spatial frequency in the contact force is the span cycle(0.02 0.03(1/m)). Fluctuations in
contact force included a dropper and hanger spacing cycles (about 0.1, 0.2(1/m)). On the other hand,
although the wear spectrum has span spacing and hanger spacing cycle components, it is not possible to
confirm the dropper space component.
When the low frequency, up-and-down 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
F = P0 - m(d2y / dt2)
(2)
where
y = Up-and-down displacement of pantograph
m = Mass of pantograph head and frame
P0 = Static upward force
In the low-frequency domain, the contact force is increased when the pantograph acceleration (d2y / dt 2)
is negative, and the contact force is decreased when the acceleration is positive. On the other hand, the
acceleration can be considered to be approximately proportional to the curvature of contact wire’s static
height profiles. As shown in Figure 3. To confirm this relation, we compared the contact force with the
curvature. Figure 5 shows the relationship between the curvature of static contact wire height profiles
and the current collection characteristics. From these figures, it can be seen that the negative higher
curvature makes the contact force large and the positive higher curvature makes the contact loss duration
time longer. Therefore, the contact force and the contact loss duration time have a correlation with the
curvature of contact wire’s static height.
3.1.2 Overlap section
At overlap sections, the contact force increases more than 270N and local wear also occurs, as shown in
Figure 3. We know how overlap structure performance influences local contact wire wear from past study
[3]. Figure 6 shows the classification of the overlap structure.
Contact wire wear
Pole
Overlap section
Contact wire static height
Pantograph height
15.5mm
15.0mm
Overlap section
100mm
100N
0N
Contact force
Contact loss
Figure 3: Contact wire condition and contact force waveform (280km/h)
1.E+04
1.E+03
Contact force
1.E+02
1.E+02
1.E+01
PSD(mm2 /Hz)
PSD(N2/Hz, mm 2/Hz, 1/Hz)
1.E+03
1.E+00
1.E-01
Pantograp
Height
h
1.E-02
1.E-03
1.E-04
0.01
Contact wire
static height
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
Contact loss
0.1
1
Wave number (1/m)
10
(1) Pantograph data
1.E-06
0.01
Contact wire wear
0.1
1
Wave number (1/m)
10
(2) Contact wire data
Figure 4: Frequency analysis of each set of measurement data
(1) Curvature and contact force at support points
(2) Curvature and contact loss duration time
at center of span
Figure 5: Relationship between curvature of contact wire height and current collection characteristics
(Contact wire and contact loss duration time was measured at 330km/h)
To confirm the relationship between the contact force and the overlap structure when the pantograph
passes an overlap section, we compared the structure where greater than normal contact force occurred
with that where normal contact force occurred. Figure 7(1) shows an example of the overlap structure
where greater contact force occurred. This figure corresponds to the right side overlap section in Figure
3, local wear occuring on the B line. This structure is equivalent to Figure 6(1). On the other hand,
Figure 7(2) shows an example of the overlap structure where normal contact force occurred. This
structure is equivalent to Figure 6(3). There is wear in the hanger space cycle on the contact wire,
however there is no local wear at the junction point. Figure 8 shows the velocity characteristics of contact
force at the overlap sections shown in Figure 7. The contact force reached 360N at the overlap section
shown in Figure 7(1) when the running speed increased to 320km/h from 280km/h. The contact force is
200N at the overlap section in Figure 7(2) at 320km/h. If the overlap structure has a good structure, it can
maintain good contact performance.
Train
A line
B line
A line
(1) Faulty structure
A line
B line
(2) Faulty structure
B line
(3)Good structure
16.0
Pole
350
Contact wire wear
15.5
300
15.0
250
Local wear
14.5
200
A line
14.0
B line
Train
150
13.5
100
200mm
13.0
0
20
40
Distance (m)
60
16.0
300
250
200
14.5
Train
150
14.0
A line
B line
13.5
0
12.5
(1) Overlap structure where greater contact force occurs
350
Contact wire wear
15.0
13.0
80
Pole
15.5
50
Contact wire static height
12.5
Residual diameter (mm)
Residual diameter (mm)
Figure 6 Classification of overlap structure
100
200mm
50
0
Contact wire static height
0
20
40
60
Distance (m)
80
-50
100
(2) Overlap structure where normal contact force occurs
Figure 7: Overlap section structure and contact wire wear
Figure 8 Velocity characteristics at overlap sections
3.2 Contact force and contact loss
Contact loss is a phenomenon of the contact force 0(N), therefore we investigated the relationship
between them. Figure 9 shows the contact force frequency distribution for cases where the contact loss
is 0% and 28%. The probability density functions calculated by the mean values and standard deviations
are also shown. In the area where 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 0.15% of the contact
force is negative. Thus, we studied the relationship between Fm-3s and contact loss. We were able to
observe a good correlation, as shown in Figure 10. 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.
Relative frequency
Probability density
Relative frequency
Probability density
┌
(1) Contact loss ratio=0%
═
(2) Contact loss ratio=28.2%
Figure 9 Contact force frequency distribution
(1) Velocity characteristics of Fm-3s and contact loss ratio
(2) Relationship between Fm-3s and contact loss ratio
Fig. 10 Contact force fluctuation and contact loss ratio
3.3 Contact force 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 300km/h [4]. If such a strain occurs repeatedly with every passing pantograph, it is
possible that the contact wire will break due to fatigue. We know that the contact wire strain is
proportional to the contact force. Therefore we observed the relationship between them. We measured
the contact wire strain together with the contact force. Figure 11 shows the relationship between the
contact force and the strain during the running test. The theoretical value was calculated by a tensioned
elastic beam model 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 shown above, the
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.
Contact wire strain ×10-6
1200
Measured value (280-340km/h) 340km/h
Theoretical value
1000
800
285km/h
600
400
200
0
0
100
200
300
Contact force (N)
400
500
Fig. 11 Relationship between contact force and contact wire strain
3. 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
ratio. 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) Contact force amplitude
It is known that contact wire strain is large at those places where 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 because the criterion of contact wire has been already prescribed as 500×10-6 in
-6
Japan. Consequently the contact force is evaluated as 180N at 340km/h against 500×10 from Figure 11.
Consequently, this value would be the contact force criterion.
The place where the strain exceeds the criterion value on the diagnosis may be the place where 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 in the 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 [5] 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) Contact force deviation
According to reference [6], 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 where s was below this value at a
running speed of 280km/h. The contact wire used on this section was newly developed PHC contact wire
(130mm 2) [7]. 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 30% can be permitted, in which case s is 70N.
4. 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.
References
[1] Kusumi, S., et al., “Measurement Method of Contact Force and Overhead Contact Line Diagnosis,”
Railway Engineering, London, England,(2004).
[2] Kusumi, S., et al., “Contact Force-based Overhead Line Diagnosis,” Quarterly Report of RTRI, Vol.47,
No.1, pp.39-45, (2005)
[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.159-162, 2000.12
[4] Iwainaka, A., et al., “Current Collecting Characteristics of Shinkansen Run at the Speed above 300
km/h,” Japan Industry Applications Society Conference, 3-23 pp.229-232, 2004.8 (in Japanese)
[5] Terada. Y, et al., “Diagnosis of Contact Line Overlap Composition by Contact Force,” RTRI Report,
Vol.16 No.6 pp.21-26, 2002.6 (in Japanese).
[6] Fujii. Y, et al., “Investigation of allowable contact-loss ratio related to contact strip wear,” J-Rail2000,
No.1409 pp.263-266 2000.12
[7] Hiroki. N, et al., “Application of Precipitation Hardened Copper Alloy to Contact Wire”, Quarterly Report
of RTRI, Vol.39, No.3, pp.142-146, (1998)