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A modern metro

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Milan Sima, railway general manager at Saft, explains how the batteries on board new trains for the Chengdu Metro will keep the system running for over 11 million people. 

By 2035 the Chengdu Metro in China is expected to carry over 14 million passengers every day with 21 lines and a total track length of 714 km.

At the moment, work is taking place to deliver 130 new trains destined for lines 5, 8 and 9. Before work can take place, there needs to be careful consideration as to how the service can run reliably and securely.

Chengdu is one of the largest cities in Western China. It’s got something for everyone, with a strong business and commercial community alongside a long history of culture and nature (it’s home to a giant panda breeding centre and nature reserve).

Being host to an urban population of 11,430,000 and more than 260 Fortune 500 companies means the roads get congested. That’s why, in September 2010, the Chengdu Metro was built. It has grown fast and it now has six lines in operation, carrying a total of four million passengers a day.

To meet its ambitious growth targets, the Metro’s engineers need to know they can rely on the systems they are specifying today for the coming decades.

Reliability and backup

As with any modern metro system, passenger safety is a top priority. It’s essential that safety, control, communication and comfort systems on board rolling stock will continue to cooperate in the unlikely event of a mains power outage. Therefore, train designers integrate backup batteries into their rolling stock.

But train designers have to consider many factors before implementing the latest and greatest security tech. First there are the challenges of limited space and pressure to minimise weight and conformance with safety standards. They also need to adopt components that provide long life, high reliability and high availability.

They have to do all of this while ensuring a low Total Cost of Ownership (TCO) and a reasonable timeframe. This means that maintenance budgets are kept in check and that trains are available for passenger services. Train builders have to rely on their suppliers to meet the manufacturing and delivery schedules, which are planned so that passengers experience reliable service from day one.

All these factors were at play for China Railway Rolling Stock Corporation (CRRC) when it was selecting the backup batteries for the 130 new trains for Chengdu Metro’s lines 5, 8 and 9. 

Adopting proven technology

CRRC selected Saft’s MSX nickel-technology battery systems. This type of battery has a compact and lightweight design, enabling CRRC to free up space and reduce the weight of the new trains without compromising backup duration or power performance.

The technology has already been proven on board the CRRC trains that are already running on lines 3 and 4. This gave the manufacturer the confidence to place a multi-million Euro, two-year contract with Saft for the new trainsets.

CRRC has deployed 434 MSX battery systems from Saft. They will be fitted to the 130 new Chengdu Metro trains, with different amounts fitted to trains on different lines, depending on the power requirements. Lines 5 and 9 will be fitted with four battery systems, while two battery systems will be fitted on the line 8 trains. Line 9 will be the first to have driverless operation, so needed extra attention in terms of performance and reliability of all the onboard systems.

These batteries are up to 40% smaller and 30% lighter than other nickel-based batteries, but still offer high-power performance and require minimal maintenance. All of the battery systems provide backup power for up to 45 minutes and the ones on board the line 5 and 8 trains will also provide traction power to enable stranded trains to travel short distances of up to 2km to reach the nearest station. The lightweight design, superior performance and exceptional reliability of these batteries has enabled CRRC to meet its objectives for low lifetime costs.

Bespoke battery systems

Another consideration for train designers is whether to outsource the complete design of a battery system or to specify all the components individually. For the Chengdu Metro trains, the cells were designed and manufactured at Saft’s specialist facility in Bordeaux, France, which has housed rail and R&D functions for 70 years. CRRC is building the cells into its own battery systems.

However, other rail programmes opt for a fully designed and tested package to fit into the space allowed. This includes all electrical and mechanical components housed in a battery box with moving tray for access. It integrates the cells, charger, electrical interface, fuses, switches and a water filling system with temperature sensors that provide data used by the charger to control charging.

Preparing for digital railways

One final consideration is the drive towards digital railways through the use of embedded sensors and condition monitoring equipment – and battery systems are no different.

Traditionally, it has been difficult to estimate the condition of the chemistry inside nickel technology batteries. Therefore, Saft introduced the COMMbatt monitoring system. This can be retrofitted to a battery system to collect real-time operational data from train backup batteries and compares it with measured performance data of rail batteries over decades. The result is a monitoring system that enables operators to shift towards preventive and condition-based maintenance.

As demand increases for smarter trains, so too does the demand for the smarter technology that makes it all happen. Smart batteries are crucial to creating the trains that customers want and need.

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