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— by Howard Ande
Freight railroads are continually upgrading infrastructure to keep pace with increased traffic demands, while electrified transit systems are using more power to accommodate growing ridership. In addition, many U.S. freight and commuter railroads continue to implement positive train control (PTC).
A number of technological advances are helping railroads keep up in those areas, including the evolution of power conversion systems.
Mostly used on locomotives and in various wayside applications, the systems can convert AC power to DC, or visa versa, reallocate electrical power or provide power conditioning for PTC components.
To better meet railroads' reliability, adaptability and durability needs — especially in light of the harsh wayside environment and growing number of sensitive PTC electronics being installed along track — power conversion systems will need to be further modified and developed, suppliers say.
Railroads are making significant investments to upgrade their infrastructure to enhance areas such as operational efficiency, safety and communication capabilities, with PTC an example of those efforts, said Mike Kania, director of business development for power conversion systems supplier Eltek, in an email.
"The power conversion equipment used to support the railway infrastructure has served it well for many years. [But] the question to be asked is whether that technology will be the appropriate choice for the years ahead," he said.
To gauge the ongoing development of power conversion systems and identify emerging trends, Progressive Railroading contacted five suppliers. Their emailed responses follow.
During the past decade, there have been "huge" improvements in the performance of propulsion packages for electrically powered rail vehicles, said Guillaume Mehlman, president of Alstom Transport North America. Most of the improvements have been driven by rail industry constituents who strived to reduce propulsion systems' cost and weight in a highly competitive market, he said.
Changes also were made to meet increased service requirements from transit agencies for more passenger capacity and comfort, and features such as onboard passenger information systems. The performance improvements are made possible by new power transistor technologies that have enabled equipment weight decreases and cost savings typically in excess of 50 percent compared with 10 years ago, said Mehlman.
"These solutions have now reached a level of maturity throughout the industry and we observe relatively standard packages being offered for most transit vehicles with solutions that are compact, lightweight, highly integrated and energy efficient, and very reliable with a clear trend towards natural cooling," he said.
At the same time, public transit agencies operating electrified transit-rail systems in recent years have expressed strong interest in improving the performance and efficiency of wayside power conversion systems to address increased ridership, provide better onboard air conditioning, reduce heat release in stations, lower operating costs and reduce energy consumption, said Mehlman. As a result, transit operators now are seeking ways to reduce energy consumption by recapturing braking energy and upgrading their electrification systems to ensure high system reliability and efficiency.
"In the last two years in the American market, we have observed a clearly emerging trend toward partial autonomy of new light-rail systems in cities and municipalities concerned with improving urban aesthetics, preserving historic city centers, minimizing carbon footprints and reducing lifecycle costs," said Mehlman.
New technologies emerging because of the trend help address specific local or infrastructure constraints, such as relocating utilities in complex intersections or managing traffic over bridges and overpasses, he said.
In terms of its own technological advances, Alstom has launched the Harmonic and Energy Saving Optimizer (HESOP), a new wayside substation
designed to capture braking energy from tramway and light-rail systems and
return it to a local power grid. The HESOP technology is capable of capturing up to 99 percent of recoverable braking energy and reducing the amount of electricity used for traction by as much as 15 percent annually, said Mehlman.
Alstom also has introduced and marketed a suite of technologies to address transit agencies' particular needs regarding partial autonomy solutions. The suite includes Supercaps for off-wire operation over short distances (typically one-quarter mile or less). The systems are compact, roof-mounted packages, such as a prototype delivered and placed in service at RATP, Paris' transit agency, said Mehlman.
Another Alstom solution: batteries for autonomy over distances up to one mile. Such a battery system has been in commercial service in Nice, France, for three years, said Mehlman.
Meanwhile, Alstom offers a Ground Level Power Supply, or APS, that's
designed to deliver power to a vehicle through a third rail in the center of the track. APS' reliability and safety have been demonstrated for 10 years in cities such as Bordeaux, France, said Mehlman. Electrical power is fed through a line about one foot underground, and includes a fail-proof transistor-based switching technology that supplies power under a vehicle's central section only.
"We feel propulsion packages or wayside power supply systems cannot be viewed or offered as commercial off-the-shelf products," said Mehlman. "They require a more comprehensive approach tailored to each city's, operator's or public transit agency's specific service requirements and environmental constraints."
Products that help railroads support their infrastructure include modular power systems (MPS) using switched mode rectifier technology that offers numerous benefits in railroad applications, said Eltek Director of Business Development Mike Kania.
"They're highly reliable and significantly more efficient than older SCR battery chargers, reducing energy consumption and cost," he said. "Their compact lightweight design and hot plug-in architecture makes the replacement of a failed module quick and easy with no need to shut down the system."
One major benefit of MPS: the systems generally include a controller that provides comprehensive monitoring, reporting and diagnostic capabilities, Kania said. The controllers can be accessed remotely, and best-in-class models provide features to maximize performance and identify impending problems before they impact operations, Kania adds.
"Given the major infrastructure investments being made by railroads, it's the appropriate time to evaluate how they will power their systems in the coming years," he said. "Modular power systems offer the operational advantages that make them a strong choice to support the evolving railroad network."
To that end, Eltek has introduced a modular power system designed to
address the needs of signaling, communications and other power conversion applications for railroads.
The company also recently introduced new American Railway Engineering and Maintenance-of-Way Association-compliant products and features for its Micropack MPS designed to address the challenging needs of signaling, communications, PTC and other rail applications requiring 12V, 24V or 48V DC power.
Micropack rectifier modules weighing a little more than one pound are convection-cooled units with output power ranging from 120W to 250W. Multiple modules can be plugged into a system to increase its capacity and provide affordable "N+1 redundancy," said Kania. In an N+1 configuration, a failure of an individual module will have no impact on load since the remaining units can provide all necessary power.
The Micropack's hot plug-in design enables a mean time to repair of less than five minutes, with no disruption to a working system, said Kania.
Because PTC radios require an isolated 12V power supply in wayside applications, Eltek has introduced a 12V DC-to-DC converter for the Micropack line. The converters can be used in conjunction with an existing DC power system at a site. Alternatively, an integrated system of both Micropack rectifiers and converters can be provided and managed by a single controller in the system.
The Micropack systems typically operate between 90 percent and 92 percent efficiency, reducing power consumption by 25 percent or more versus the most widely used solution, said Kania.
Monitoring of the Micropack is performed by the Compack controller, which provides technicians both local and remote access to comprehensive monitoring, reporting and diagnostic information via an Ethernet (web browser) interface. The Compack controller has extensive battery management and monitoring capabilities to ensure battery life, and detect and identify problems before a field emergency occurs, said Kania.
There are concerns that single points of failure could potentially be introduced with PTC implementation, resulting in overall performance being compromised, he said. For power conversion systems' reliability and performance, this means moving from a conventional monoblock battery charger, with very limited monitoring and reporting capability, to modular power systems with rectifier/converter redundancy and advanced monitoring and control capabilities, said Kania.
"The Micropack system has been designed in response to those demands," he said. "The Micropack system is either in lab evaluation, field evaluation or actual deployment at nearly all the major railroads and many transit systems."
Higher power, modular multi-output and low-input total harmonic distortion (THD) are emerging trends impacting technological developments with power conversion systems and equipment, said Sue Mayrand, vice president of sales, rail and transit for Schaefer Inc.
The company has introduced Digital System Processing-based front ends to keep input THD at a minimum.
In addition, Schaefer has introduced small inverters targeted for railroad applications in the 700-to-3000W range.
"Schaefer has seen customer demand increase for products that can provide output power during engine cranking, 72V, 37.5V, and 600V DC inputs, an ability to install components under cars, and the ability to survive input transients when in use," said Mayrand. "We meet all these needs with different converter, inverter and battery charger solutions."
Schaefer is a build-to-order company, providing "the ultimate flexibility" to meet customers' needs, she said.
"We can add options, change 'standard' electrical specifications and build new mechanical packaging to meet project needs," said Mayrand. "We do this to some degree with almost all [products] we manufacture."
One trend noted by Arthur N. Ulrich Co. is an increasing interest in high-frequency technology in the area of battery charging, converters, inverters and controllers. A high-frequency design can improve operational efficiencies and the power factor, while also significantly reducing the size and weight of equipment, said Arthur N. Ulrich Chief Executive Officer Tom Ulrich.
"The trick is to balance these benefits with the long-term reliability and survivability of the products in harsh rail environments," he said. "Ultimately, the key is to provide a design and 'topology' that will provide the advantages of the new technology with the reliability provided by the technology it replaces."
In the wayside and communications battery chargers sector, Arthur N. Ulrich principal La Marche Manufacturing Co. has offered several new battery chargers and inverters featuring advanced high-frequency designs and various communication interfaces.
The chargers are smaller in size and lighter in weight, and offer "unique capabilities," such as an integrated AC and DC power system on a common frame with an assortment of options, said Ulrich.
The company also has upgraded its solar control system standards to incorporate Max Power Point Tracking (MPPT) controllers, which feature advanced DC-to-DC conversion technology, enabling Arthur N. Ulrich to utilize more cost-effective, higher voltage solar modules, he said. The customer then can reduce interconnect wiring costs and capture a wider range of the available solar energy spectrum, Ulrich adds.
Customers also are requesting more capability to monitor the health and status of equipment remotely to allow more proactive maintenance and servicing.
"They are looking for greater simplicity in configuration and setup, smaller equipment sizes, reduced weights for ease of handling and better output filtering for compatibility with the input power requirements of the more sophisticated equipment being deployed," said Ulrich. "At the same time, they want solid dependability in the harsh railroad wayside environment."
To meet those needs, Arthur N. Ulrich offers product variations tailored to a customer's wishes, which often involves adding a feature or two, he said.
"On at least one occasion, we have even removed some product features and options that were considered extraneous for desired cost savings," said Ulrich.
In terms of upgrading existing products, Arthur N. Ulrich has added surge and lightning protection and specific communication protocols, optimized transformers in its rectifiers and inverters, and expanded the power ranges of some products to more closely match customers' requirements.
Ulrich's customers include most of the Class Is, many transit authorities and many major signal system suppliers.
"It is important to realize that this equipment is absolutely critical to the power backbone that keeps the trains running," said Ulrich. "Just because technology allows us to add many more bells and whistles than we could in the past or shrink equipment sizes and weights dramatically, this should always be balanced against any tradeoff in system reliability and robustness."
With electronic equipment in general, the emphasis continues to be placed on providing more products in a smaller package at a lower cost, said John Thompson, a spokesman for Wilmore Electronics Co. In the harsh electrical and mechanical environments found in rail applications, design conservatism and circuit protection is critical, he said.
Advances in the power semiconductor industry, such as silicon-carbide rectifiers, lower-loss metal-oxide semiconductor field-effect transistors (MOSFETs) and high-voltage schottky diodes "are allowing us to make improvements in power conversion efficiency and package size without sacrificing reliability or protection," said Thompson.
Railroads' efforts to implement PTC have accelerated an already growing trend toward more sophisticated and capable electronic systems both onboard and trackside. The systems are usually in need of some type of power conditioning, said Thompson.
For example, Wilmore recently introduced a new series of small and inexpensive DC-to-DC converters (Wilmore series 1737) designed to power 74V DC PTC radios and electronics on hi-rail and track maintenance vehicles with 12 and 24V DC electrical systems, he said.
"Beyond the paramount requirements of reliability of the power conversion system and protection of the equipment that it powers, one of the requests we've received more regularly from customers is to provide power converters that can deliver full output power through locomotive cranking events," said Thompson.
During cranking, a 74V DC locomotive power bus might dip to as low as 20V DC for several seconds, too long for the hold-up times of traditional power converters, he said. A power system that can operate down to 20V DC on its input can allow important systems to continue to function through these events, Thompson adds.
"This capability is growing in importance as more and more electronic systems find their way into the locomotive environment, he said. "Wilmore has developed equipment to meet this demand and function requirements."
In addition to equipment developed to maintain power integrity in locomotive cranking events, Wilmore recently repackaged converters for 12V DC signal battery isolation, with various features to satisfy individual railroads' needs.
"As railroads continue to pursue higher reliability of service, greater throughput of freight and passengers, improved operating safety and more competitive cost structures, sophisticated electronic systems are sure to be a growing part of the solution," said Thompson. "The demanding operating environments will continue to encourage the use of conservatively designed and well protected power conversion equipment and, this will continue to be a major area of emphasis and expertise at Wilmore Electronics."
Howard Ande is a Bartlett, Ill.-based free-lance writer.