As the rail industry in Australia and New Zealand continues to evolve, the importance of efficient and reliable electrification planning cannot be overstated.
At the heart of this transformation lies the role of static frequency converters (SFCs), a critical technology that ensures the seamless integration of electrical power into rail networks.
SFCs play a crucial role in modernising and stabilising power systems, making them vital components in the transition to greener and more efficient rail networks.
High-performance electrification solutions can increase capacity, cut costs, and propel networks into the future.
They are pivotal in maintaining a balanced load on the three-phase supply network, thereby enhancing power quality and operational efficiency. By eliminating the need for harmonic filters and output transformers, SFCs can reduce carbon footprints and simplify the infrastructure required for modern rail systems.
But what are SFCs, and what can they do? To find out more, Rail Express spoke to two experts from Siemens Mobility Australia and New Zealand – Leo Beyers, Head of Rail Electrification, and Peter Wagner, Engineering Project Manager.
What is an SFC?
Traction power supply systems consist of many components that must interact seamlessly with each other. Traditionally the rail network has taken power from two phases, creating what is known as an ‘unbalanced load’.
An SFC eliminates this by converting the three-phase inputs into a single-phase current.
To put it simply, Wagner said: “Whilst providing the required power to the traction power network, SFCs provide a balanced load to the three-phase power supply network, which in turn provides good power quality back to the network provider, resulting in cost savings for the operator.”
Essentially, SFCs consist of only one converter, which directly couples two networks. Three-phase AC voltage is converted into single-phase AC at the required voltage and frequency.
Beyers said that with conventional power transformers, there is a reticulation of energy (the system of infrastructure and processes used to distribute electricity from a power source to the end-users), from a grid supply of 132 kilovolts, 66 kilovolts, and even 33 to 25 kilovolts.
“A 25-kilovolt AC system is the most well-known, internationally established means of power transfer to a network of trains.
“With conventional power transformers, this is achieved via step-down transformers – that step down from high voltage to medium traction supply voltage – and then the isolators, disconnectors, and switch gear are used to control and manage the assets.
“Static frequency converters are a bit more complex, but they are now being seen as the new ideal, because they are a highly innovative approach that present a number of benefits.”
The move towards SFCs
“In Australia and New Zealand, but also internationally, rail operators are moving towards this new technology that provides a controlled power supply which can be easily adapted and managed whilst ensuring stable operations,” said Beyers.
“Rail operators have identified key benefits from the use of SFCs, which include life cycle cost benefits, maintenance savings and increased availability of the traction supply network.”
As rail networks are electrified to support net zero strategies, future electrification systems need to be able to scale capacity while maintaining the highest availability possible to ensure punctuality and energy efficiency. Grid providers are also increasingly demanding a balanced load with low harmonics. In the future, the operational goals of the system will vary more than they do today; making quick adjustments a key requirement.
Siemens Mobility has successfully deployed SFCs across numerous projects internationally, including in Germany, the United Kingdom and soon in New South Wales.
“In the United Kingdom, for example, we were able to boost efficiency on the network by using SFCs to create a balanced load,” said Wagner. “This project has had considerable cost savings for the rail operator.”
Beyers said the rail industry’s migration towards SFCs has been happening over the past 10 to 15 years due to the increasing demands by grid operators to manage the load. There has been more momentum recently because a more innovative version of the Direct Current (DC) link converter has been released, which is an electrical module that acts as an intermediary, temporarily storing energy to allow for efficient power transfer and control.
“This is called the MMDC or modular multi-level direct converter, and it uses Insulated Gate Bipolar Transistors (IGBTs) and power semiconductor devices that act as high-speed switching elements in electronic circuits,” he explained.
“Transistors have lower losses than the thyristors used on older SFCs. This higher efficiency translates into cost savings and a reduction in rail’s carbon footprint across the equipment’s service, while its self-healing technology improves system reliability.”
Beyers said Siemens Mobility has adopted MMDCs as an alternative because they make energy management simpler.
“The older DC Link technology can present challenges, which MMDC technology eliminates,” he said. “The topology of traditional DC-Link technology using thyristors as switching devices can affect availability. If one switching device fails it takes some time before traction supply is restored.
“With MMDC, if one IGBT module fails, it doesn’t affect the others because the defective module is automatically bypassed, maintaining the series configuration.
“The SFC continues to provide power to the network and the replacement of the faulty module can be scheduled for a time convenient to operational requirements. The modular approach also makes replacement quick and easy to minimise any down-time. So, it’s a lot more resilient.”
He said that operators can opt to move from DC Link technology to MMDC, and this will help them vastly improve their asset management life cycle.
“When it comes to efficiency and availability, you don’t want to be using old technology.”
Cutting costs and boosting efficiency
Beyers said operators’ potential cost savings is driving growing interest in SFCs in the rail industry.
“SFCs require an initial investment, but then you really reap the benefits with savings over the entire life cycle of the asset,” said Beyers.
SFCs also offer operators a streamlined, more efficient process. Distance between SFC substations can be increased due to dual side feeding and there is a significant improved volt drop over the line length.
“With a conventional traction power substation, you are only taking two phases out of the three from the national grid,” Beyers said.
“The problem with that is that you have to meet regulatory requirements with the grid supply authority or network distribution operator, and you have to agree on specific power transfer arrangements – for example, harmonics and negative phase sequence. This can be quite exhaustive and painful, and if you don’t meet them, there are penalties. The beauty of SFCs is, you don’t have to worry about that. It’s really simple to manage with the power industry.”
Beyers said SFCs remove the need for additional monitoring equipment in substations, as well as a cubicle that is shared with local power authorities.
“With SFCs you can have a smaller substation footprint,” he added.
Operators can also save time and money when it comes to maintenance.
“You have fewer assets that can fail, and if they do fail, there are backup components and systems to ensure continued operation, so it’s quite unique.”
Beyers said there are also advantages when it comes to the connections to the railway or Overhead Line Equipment.
“There are benefits in how the static frequency converter protects both directions of an electrical section,” he noted.
“So, one can avoid the need for overhead line (OLE) discrete assets such as neutral sections.
“Put simply, that’s an intricate OLE configuration that you no longer need, that you would need at a conventional power transformer substation to maintain safe electrical phase separation.”
SFCs can also reduce harmonics – interference on the electrical network.
“If you reduce harmonics, again it improves efficiency and saves you money,” said Wagner.
“There are also limits to the amount of harmonic interference that is allowed, and if you don’t meet that, you will need to spend more money on additional equipment.”
With less equipment, there is less of a risk of faults.
Reducing greenhouse gas emissions
Wagner said MMDCs can lead to up to 10 per cent increase in energy efficiency, which means lower carbon emissions, as well as lower operational costs.
There are additional environmental benefits. “Siemens Mobility has a layout where we don’t need an output transformer, we use a reactor instead,” said Wagner.
“The carbon footprint of a transformer is much higher than that of a reactor – almost tenfold. So having the option of using a reactor makes a big difference when it comes to decarbonisation.
“In the design stage of one project a comparison between the DC-link and MMDC layout was made, showing a reduction of 30 per cent of the power modules when using MMDC. This is not just a significant reduction in carbon footprint but also positively affects the physical footprint of the converter station.”
Supporting railways
Beyers said Siemens Mobility has the skills and knowledge to support operators with their long-term power supply upgrades.
“If you are considering to expand your network, you’re going to need one or more grid supply points, and that’s where SFCs will provide significant savings long-term,” he said.
“The reduction in equipment needed, the lack of maintenance required and the improvements in efficiency all add up to a cost-efficient solution.
“For years, all around the world, Siemens Mobility recognises the need to increase value sustainably over the entire life cycle, and we are here to help.
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