Electrical systems specialist, Mersen has developed a monitoring system adapted for current collector devices used in subway and metro systems
The third rail is just as essential for subways and metros as the overhead wire is for long-distance and high-speed trains: both supply electrified trains with electricity. Running along the railroad line, the third rail carries the current while the current collector collects it when sliding along the power rail. The current drawn is transferred to the rail vehicle by a collector shoe usually made of copper impregnated graphite. Two rugged coil springs fitted on the current collector ensure constant contact of the shoe against the power rail.
This physical contact paired with a voltage of 750 V, the often-considerable speed of the trains, and places of unevenness on the third rail contact surface are all factors responsible for the significant wear sustained by the collector shoes fitted on every train.
“The shoes are generally replaced every six to twelve months. However, Mersen’s shoes do last longer”, explains Mersen Sales Manager François Trama. Nevertheless, the shoe represents 70 percent of the total cost of ownership of the entire current collector device (CCD) during its lifespan.
Boosting efficiency and sustainability
“After investing nearly four years of hard work, our project team has now devised a solution that will dramatically improve the comprehension of the CCD’s performance on duty”, declares Mechatronic Engineer Bilal Naim. Mersen’s solution to the problem is the D-CCD, the Digital Current Collector Device. This device is used for realtime monitoring of the contact force between the shoe and the power rail.
The clearly visible portion of the D-CCD is a black box, which is attached to the arm of the current collector and houses the so-called MAT, the Module Acquisition & Transmission. The MAT is composed of the readings recorder (strain gauge and temperature sensor) and of an electronic system that is in charge of processing the signals, storing the data and providing the wireless communication. The measured variables are
- the temperature rise in the current collector (if one collector of the car is off),
- the force applied on the third rail by the shoe (N),
- the shocks and vibrations applied to the current collector during its course and
- Optical sensors.
The optical sensors serve as arc detection where one can detect the peak of lights generated by arcs taking place at the shoe vs. power rail contact.
All these data serves as indicators for the condition of the collector shoe, the collector overall and indirectly of the third rail. “This information allows us to find out if the shoe is still operational or will have to be replaced shortly. It gives a clear insight of the quality of the third rail”, reveals R&D Department Manager Olivier Dosda.
Challenges during development
The development of the measuring technology for the MAT posed a tremendous challenge to Mersen’s engineers. “The goal to measure the contact force with the greatest possible accuracy required us to be as close to the contact point as possible, but the voltage of 750 V also made it necessary to provide for dependable insulation”, explains Olivier Dosda. “Two objectives hard to combine.” Similarly challenging was the development of an electronic module capable of working reliably in a difficult environment marked by high voltage, high level of shocks and vibrations, and electromagnetic effects.
The solution developed by the engineering team features a specially designed strain gauge technology using thick-film strain gauges. Patented in 2018, this advanced technology detects deformations in the current collector arm during operation. Thanks to its electrical isolation properties, it can be safely applied to electrified current collectors, allowing precise characterization of impacts occurring between the current collector shoe and the electrified third rail during operation.
The MAT module is battery-powered and designed with its own data storage. “These properties make it a stand-alone unit without any connection nor interference with the train, which was of great importance to us”, underlines Olivier Dosda. Its power supply and data capacity are enough for one day of operation. Customers who wish to test-drive the system for a day and check the condition of their power rail / current collectors can be accommodated by Mersen with a workable solution that can easily be integrated into Mersen current collectors via plug-and-play.
Analysing wear behaviour
Those interested in monitoring their current collectors continuously will require to connect the train network to the MAT via an ethernet cable and a 24 V supply voltage. This interface that the MAT calculator provides will transfer the data directly to the train system and extend the real time measurement as long as it needs to.
“This long-term monitoring feature in particular is what creates the best prerequisites for analyzing the wear behavior of the current collectors and for drawing the appropriate conclusions”, states Olivier Dosda. “We aim to eventually arrive at predictive maintenance including plannable maintenance intervals, which will allow our customers to operate their trains with improved reliability and reduces total cost of ownership.” And as far as the benefits for themselves are concerned, Mersen is hoping that the data collected by the D-CCDs will help them optimize the design of their current collectors.
High-efficiency solution
As a global expert in electrical energy and advanced materials in high-tech industries, Mersen ranks among the world’s leading suppliers of current collectors for use in subways and metros. “With the D-CCD, we are now offering our customers an exceedingly appealing high-efficiency solution that will give them an insight of what is going on between the 3rd rail and the carbon shoe which is the stepstone towards shoe life extension.“
Mersen unveiled the Digital Current Collector Device in September 2024 at InnoTrans in Berlin, where it managed to “electrify” the visitors of the world’s leading trade fair for transport technology. It was also met with great interest at a roadshow through Southeast Asia. This is also the region that placed the first customer order. A manufacturer from Korea will build the D-CCD into trains operating in the service of the Singapore subway system. “The wait for the first feedback from use in the real world is keeping us at the edge of our seats”, announces Olivier Dosda.
For more information, visit Mersen
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