Adoption of Overhead Rigid Conductor Rail System in MTR Extensions

Journal of International Council on Electrical Engineering
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Adoption of Overhead Rigid Conductor Rail System
in MTR Extensions
Man Kit Mak
To cite this article: Man Kit Mak (2012) Adoption of Overhead Rigid Conductor Rail System in
MTR Extensions, Journal of International Council on Electrical Engineering, 2:4, 463-466, DOI:
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Journal of International Council on Electrical Engineering Vol. 2, No. 4, pp.463~466, 2012 463
Adoption of Overhead Rigid Conductor Rail System
in MTR Extensions
Mak, Man Kit†
Abstract – The conventional overhead catenary system for both 1500V d.c. traction system and 25kV a.c.
traction system have been used in the existing railways of Mass Transit Railway Corporation Limited
(MTRCL) in Hong Kong for over 20 years. Another type of overhead line system, the overhead rigid
conductor rail system has now been increasingly used in the tunnel sections of underground metro system
in Europe, Mainland China and South Korea. The non-tension and low resistance characteristics of the
rigid conductor rail system have advantages in enhancing and improving various aspects including energy
efficiency, reliability, maintainability and availability of the overhead line system. This paper gives an
outline of the overhead rigid conductor rail system and the benefits of adopting such system for the new
MTR extensions including West Island Line, Kwun Tong Line Extension, South Island Line (East) and
Shatin to Central Link. The result of simulation study to demonstrate the acceptable dynamic
performance for the interface with the pantograph of rolling stock for line operating speed up to 130kph
is included in this paper.
Keywords: Rigid conductor rail, Catenary, ORCR, OCS
1. Introduction
The Overhead Rigid Conductor Rail (ORCR) System for
railway has been used in Europe since the 80’s. It has
been adopted in the tunnel sections of underground metro
system in the low voltage range from 750V d.c. to 3000V
d.c. and for heavy rails at the high voltage range from 15kV
a.c. to 25kV a.c.
The ORCR system for 1500V d.c. system and 25kV a.c.
system inside tunnels has been widely adopted, not only in
Europe, but also in Asia, especially in Mainland China and
South Korea.
The operating speed for ORCR system has been up to
100kph for d.c. system and 160kph in a.c. system.
There are benefits in adopting ORCR system in MTR
extensions as compared to the conventional overhead
catenary system (OCS) which have been used in existing
railways for both 1500V d.c. system and 25kV a.c. system
for over 20 years. The benefits include capital cost saving
and improvements in energy efficiency, maintainability,
reliability and availability.
2. General Description of ORCR System
Corresponding Author: Project Division, MTR Corporation Limited ,
Hong Kong ([email protected])
Received: September 27, 2012; Accepted: September 28, 2012
The ORCR system comprises an aluminium conductor
profile with a copper alloy grooved contact wire inserted
with special conducting grease at the bottom pinch as
shown in Fig. 1.
The characteristics of the aluminium conductor profile
are summarised as below:
Nominal Cross sectional area
Profile Height
Top Width
Vertical Inertia
Horizontal Inertia
Module of elasticity
Coefficient of linear expansion
Maximum Resistance at 20oC
2214 mm2
110 mm
85 mm
5.9 kg/m
110 cm4
335 cm4
69000 N/mm2
24 x 10-6 oC-1
This profile bears similarity to the messenger wire in
conventional overhead catenary system (OCS) in supporting the contact wire and has been standardised among
different manufacturers. The aluminium conductor profile
as well as the contact wire need not be in tension to
maintain the required level. Thus there is no tensioning
device such as balance weight assembly and associated
termination accessories for the ORCR system.
The continuous current rating of the standard rigid
conductor rail, i.e. the aluminium conductor profile with the
single contact wire is 3,000A and the resistivity at 20oC is
0.032Ω-mm2/m. This capacity is particularly advantageous
for metro with 1500V d.c. system where high current
Adoption of Overhead Rigid Conductor Rail System in MTR Extensions
capacity is required. For the 1500V d.c. 3000A OCS, a total
of six overhead copper wires including 2 x 120mm2 contact
wires plus 4 x 150mm2 messenger/auxiliary feeder wires
are needed to achieve the required capacity. In addition, the
copper loss of ORCR system is about 40% less than OCS
for 1500V d.c. system due to its lower resistance.
Fig. 2. Arrangement of transition section.
Fig.1. Cross section of aluminium conductor profile.
Staggers, which are arranged in a zig-zag manner on
conventional overhead catenary system to spread the wear
on pantograph carbon strips, will be configured in a
sinusoidal curved shape in ORCR system. A maximum
off-set value of about 250mm and 400mm from track centre
is normally adopted to spread more evenly on the carbon
strips for 1500V d.c. system and 25kV a.c. system
There are two types of transition arrangements which
will allow smooth passage from catenary system to ORCR
system and vice versa without creating hard points in the
(1) Transition Section – It gradually reduces the inertia and
increases the flexibility as it gets near the conventionally suspended contact wire by the progressively
cutting out the profile to enable smooth transition from
OCS to ORCR and vice versa. This transition section
arrangement is shown in Fig. 2 and has been widely
(2) Parallel Running of Two Systems – The two systems are
arranged in parallel and mechanically separated from
each other. The arrangement is shown in Fig. 3. In the
overlap section, the catenary contact wire is gradually
increasing its inertia and flexibility to match with
ORCR to allow smooth transition from one system to
Fig. 3. Paralleling the two systems as transition.
Hinged Arm Arrangement for 25kV a.c. System
Roof Mounted Arrangement for 1500V d.c. System
Fig. 4. Supports for ORCR system.
These transition devices are proven in numerous d.c. and
a.c. traction railway projects for passing from OCS to
ORCR and vice versa.
The aluminium conductor profile as adopted in 1500V
d.c. system is similar to the 25kV a.c. system. The only
difference between 1500V d.c. system and 25kV a.c.
Mak, Man Kit
system is the support arrangement of the aluminium
conductor profile. In 1500V d.c. system, the profile is
normally suspended from the roof whilst hinged arms are
used in 25kV a.c. system in order to reduce the headroom
requirement. The two typical support arrangements are
shown in Fig. 4.
3. Simulation Study on ORCR and Pantograph
Interface Performance
Computer simulation studies have been carried out to
ensure the ORCR and pantograph compatibility. The model
of the pantograph mounted on the existing IKK trains
which are running on the West Rail Line in Hong Kong was
adopted. Maximum operating speed of 130kph with 400mm
stagger was simulated.
The simulation study was performed on the interaction
between pantograph and the ORCR system based on
various considerations, such as turnout location, transition
section from conventional catenary system to ORCR
system, section insulator, ORCR expansion joint and
neutral section location. The results of the simulations for
the transition from OCS to ORCR and the neutral section
location are highlighted in Fig. 5 and 6 respectively.
The simulation results indicated that the contact force is
positive and below the maximum contact force of 250N for
operating speed up to 130kph. The dynamic behaviour of
the pantographs is satisfactory and fully complies with the
international standard EN50119 “Electric Traction
Overhead Contact Lines”.
Fig. 6. Contact force of pantograph – neutral section.
4. Maintainability, Reliability and Availability
4.1 Maintainability
The conventional catenary system requires many differrent types of components. The ORCR system will only
require fewer components (less than 30 items). As the
aluminium conductor profile is tandardized among different
manufacturers, the components from different manufacturers are interchangeable. Thus, the inventory of spare
ORCR components will be relatively less as long as
significant length of ORCR is installed.
In general practice, the average percentage worn out of
the cross sectional area of contact wire before replacement
is 20% for OCS. As the contact wire for ORCR system is
non-tensioned, it is acceptable to have worn out up to 50%.
The service life of the contact wire for OCS is around 25
years whilst service life of 30 years is expected for ORCR
The maintenance cost of ORCR system will be much less
than that of the OCS. The maintenance cost of ORCR
system is about one-third of that for OCS.
4.2 Reliability
Fig. 5. Contact force of pantograph – transition from OCS
to ORCR.
The major advantage of ORCR system is its nontensioned characteristic. It will not cause the dewirement
of contact wire, which normally results in severe damage of
overhead line system and train disruption. In case a
support of a span length of ORCR fails, the adjacent
supports on both sides will temporarily hold the system and
the train will still be able to pass through the faulty ORCR
section at a reduced speed.
Adoption of Overhead Rigid Conductor Rail System in MTR Extensions
From experience, components fell down fouling the
pantograph and the associated chain effect is the major
factor in reliability. ORCR requires less components and
moving parts compared with OCS and thus will improve
the reliability.
Another major characteristic of ORCR system is its fire
withstanding performance inside the tunnel. With the same
fire intensity, the tensioned overhead catenary wires will be
broken whilst the ORCR system can stay intact and ready
for use after cooling down.
4.3 Availability
In case of overhead line incident, the extent of damage
on ORCR system will be limited whilst the extent of
damage on OCS will involve one tension length. The
recovery time taken for the replacement of ORCR system
compared with the conventional catenary system will be
much shorter. The recovery time can be reduced from
several hours to less than an hour.
5. Capital Cost Saving
The major capital cost savings for the adoption of ORCR
system are as follows:
Elimination of the tunnel niches to house the tension
weight assemblies.
Reduction of headroom for overhead line equipment
installation zone in tunnel leading to a small tunnel
diameter. The internal diameter of the bored tunnel using
Tunnel Boring Machine (TBM) construction method can be
reduced from 6.84m to 6.3m by adopting ORCR system as
compared to OCS for 25kV a.c. system.
6. Application to MTR Extensions
There are four new extensions including West Island
Line (WIL), Kwun Tong Line Extension (KTE), South
Island Line (East) (SIL(E)) and Shatin to Central Link
(SCL) in Hong Kong. The West Island Line is under
construction phase and the other three extensions are under
design phase.
The traction system, operating speed and alignment
adopted for the four new extensions are summarised as
1500V d.c.
1500V d.c.
1500V d.c.
25kV a.c.
Operating Speed
80 kph
80 kph
80 kph
130 kph
Tunnel/ Viaduct
Tunnel/ Viaduct
The ORCR system can be fully applied to the four new
extensions according to the operating speed, traction system
and alignment adopted for the extensions.
The total construction length of the 1500V d.c. ORCR
system is about 20km for WIL, KTE and SIL(E) and the
total construction length of the 25kV a.c. ORCR system is
about 32km for SCL.
7. Conclusion
The ORCR system will be adopted in the four new MTR
extensions. The benefits of adopting the ORCR system are
summarised as below:
• The ORCR can significantly reduce the chance of
dewirement due to non-tension characteristics of the
contact wire under fault and fire incidents.
• Recovery time from OHL incidence can be reduced from
several hours down to less than an hour.
• ORCR can achieve higher reliability than those of OCS.
• No hard points will be introduced in the transition
sections from OCS to ORCR systems and vice versa.
• The copper loss for ORCR system is less than OCS to
provide good energy efficiency.
• Good current collection between pantograph and contact
wire under dynamic conditions for speed up to 130kph.
• Overall project cost saving for using ORCR system can
be achieved as tunnel size is smaller for 25kV a.c. system
and niches to house balance weight assembly can be
• Reduced maintenance cost as compared to OCS.
Mak, Man Kit received MSc degree in Control System
from Imperial College of Science and Technology, University
of London.
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