RAIL FEATURE
Improving performance and reducing cost for the rail industry
Elizabeth Da Silva, high voltage development engineering manager, TE Connectivity, explains how a new-generation roofline module can improve the aerodynamic performance of trains, and how TE is bringing new products to market faster than ever through its dedicated test centre
R
oofline systems are critical to the operation of electrified trains. They
transmit high-voltage power from the pantograph on the roof to the traction transformers, and are traditionally made up of air-insulated components, such as switchgear, insulators, intercar cables, surge arrestors, bushings and downleads. They also include cable, copper braid and even the nuts, bolts and supports that hold connections in place. Such systems are tested to their limits on top of trains. Not only do they experience mechanical shock, vibration, overvoltages (lightning and switching transients, for example), fast airflows, adverse weather, and temperature fluctuations, they often operate in a variety of environments that can affect electrical performance, such as pollution, humidity, and high altitude or low pressure. This is key as air quality affects the performance of high voltage systems by reducing the insulating ability of air. As railway systems are now being
developed in parts of the world where pollution, humidity, salt-laden air and high altitudes are common, it has become more important to engineer roofline systems for each line. Failing to do this can result in flashovers, when current jumps through the air from the electrical conductor to the roof of the train. This short circuit causes loss of power and stops the train, disrupting timetables and services, and ultimately affecting the train operator’s reputation.
IMPACT OF SMALL DESIGN CHOICES Over many years TE has worked with train manufacturers to reduce the likelihood of roofline system failures.
Flashover elimination is part of this objective. Usually this means scaling up air gaps to increase insulation and choosing only high-quality components - from appropriated polymers, down to the connecting braids, supports, nuts and bolts. Even these simple components are important. For example, a nut made of low-grade steel can corrode and destroy high- value components. Alternatively, loose strands of a low-
quality copper braid can reduce the air clearance and cause the electric field to concentrate, increasing the likelihood of flashover. Alternatively, sharp edges on a support structure, or any pointed components, will also concentrate the electric field which is why high voltage systems use smooth rounded corners.
A NEW GENERATION OF SYSTEMS Recognising the potential for a step- change in technology, TE introduced a new-generation roofline module at InnoTrans in 2016. The new module completely replaces the individually engineered air-insulated approach and is designed for all platforms that operate at 25kV and 15kV. It is also designed to be low-profile,
lightweight and reliable in spite of harsh environmental challenges. The biggest advantage is energy savings from improved aerodynamic performance. Reducing the overall height of rolling stock, but reducing the height is also helpful for double decker rolling stock or lines with height restrictions. Lower weight is also an advantage. At its core, the new-generation roofline
module uses solid dielectric insulating materials, replacing the traditional air- insulated approach. Depending on the configuration and components, it is less than half the height and weight of the previous best in class roofline systems.
Up to 60 per cent of traction effort is
lost to aerodynamic drag and friction in intercity and high-speed trains, so any measure that reduces drag improves performance and the financial bottom line for operators.
ACCELERATED TEST PROGRAMME As well as creating a working prototype, TE also developed a Rail High Voltage Test Centre in Swindon to perform tests on the module, and other products, under a harsh regime of tests that evaluate performance against real-world operating conditions experienced in rolling stock applications. The test centre was opened in July 2016 to reduce time to market for new products. There can be long delays in testing at external facilities and it is essentially a pass or fail process, giving little insight into how to improve designs. By bringing significant testing in house, TE can develop products around 30 per cent faster. The test centre includes equipment for
electrical, mechanical, thermal, environmental and multi-stress testing. These mimic the harsh conditions experienced on the railway. One highlight of the facility is an impulse generator that tests components against lightning impulses of up to 300kV and switching transients up to 100kV. This accelerated programme of
laboratory testing will prove performance before on-board testing. The ultimate goal is for the first unit to enter commercial service in 2018, and to open the potential for train manufacturers to offer better aerodynamic performance, weight and space saving, to train operating companies, as well as energy and cost savings.
TE Connectivity
www.te.com
ELECTRICAL ENGINEERING | MARCH 2017 39
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