Safety critical power for Vienna’s underground

In many major cities around the world, underground railways are fundamental to green mobility and economic growth. The Wiener Linien rapid transport system in Vienna, for example, connects around 450 million passengers to nearly 100 stations every year and is expanding. But with each of these subterranean stations dependent on the public power grid, an outage could spell disaster for the city's inhabitants who need a safe route to street level.

To ensure that every light, escalator, automatic door and signalling system remains operational in the event of an emergency, our Rolls-Royce Power Systems team have been developing a sixth emergency genset to join the five already installed on Vienna’s network.

A compact but powerful solution

The mtu Series 956 genset unit is an imposing sight, standing at 3 m high, 5 m long and 2 m wide and weighing in at 21.5 tonnes. “Sure, it's a huge engine, but in terms of the output it's capable of it's pretty compact,” points out Giovanni Coiro, Sales Manager Power Generation at Rolls-Royce Power Systems.

That output is 5,000 kW. Spread over 16 cylinders, the 956 engine boasts an incredible power-to-weight ratio. “Exactly the reason we want such engines in our emergency generator sets,” adds Gerald Leutgeb, head of the Electrical Plant division of Wiener Linien, Vienna's public transport operator.

Five mtu engines are already in service in the engine rooms deep in the belly of the Wiener Linien. This sixth unit is already en route to Vienna and will be ready for service in late 2022. Having left the Rolls-Royce factory in Friedrichshafen, the engine will visit the site of mtu sales partner K&W Drive Systems, who will be working on the final integration with Austrian electric power generation expert, ELIN.

Keeping the lights on

Together, the gensets will be capable of delivering 30,000 kW of power to keep the stations fed with energy should the public power grid fail. Lifts, for example, will move to a predefined level and open their doors automatically to allow passengers to exit while the station lights remain fully on, illuminating safe passage to exits.

Up to 2 MW of power per service line is required to supply enough electricity to each underground station. While this isn’t enough to operate the trains themselves, these come to a standstill in the event of an outage, with only certain units continuing to run to bring passengers to the next station for their safe evacuation. 

Engineering to depend on

Thankfully, most engines installed in emergency gensets rarely need to be used. But when the case does arise, they have to be able to step in immediately. In Vienna, the mtu engines can ramp up to maximum power output in less than ten seconds and tests are performed every month to check that they're always operational. Additionally, all six engines are connected so that, in the unlikely event of a technical issue with one, the others will switch on in its place.

“We've been lucky enough never to have suffered a serious power outage,” reports Gerald Leutgeb. “But if it does happen, I have 100% faith in the engines.”

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