In the world's major cities, underground railways are fundamental to green mobility. As such, they are being expanded in many places, including Vienna, where a new line – the U5 – is being built. With further subterranean stops, the city's inhabitants gain more points of access to the service. And to ensure that the lights never go out in the underground and that people can exit safely in the rare case of a power outage, five emergency gensets are in service there, soon to become six.
An mtu Series 956 unit is an imposing sight. Stand next to it and its sheer proportions – 3 m high, 5 m long, 2 m wide and 21.5 tons in weight – make you feel like you're looking up at a giant. “Sure, it's a huge engine, but in terms of the output it's capable of it's pretty compact,” pointed out Giovanni Coiro, Sales Manager Power Generation at Rolls-Royce Power Systems. That output is 5,000 kW, which, spread over 16 cylinders, means the 956 engine boasts an incredible power-to-weight ratio. “Exactly the reason we want such engines in our emergency generator sets,” said Gerald Leutgeb, head of the Electrical Plant division of Wiener Linien, Vienna's public transport operator.
30,000 kilowatts for safe evacuation of the stations
Five mtu engines are in service in the engine rooms deep in the belly of the Viennese underground. A sixth is scheduled for next year. This unit has already left the Rolls-Royce factory in Friedrichshafen and is currently on the site of mtu sales partner K&W Drive Systems, who is working with Austrian electric power generation expert ELIN to integrate it into the plant as a whole. The new emergency generator set is to be ready for service towards the end of the year.
Together, the generator sets will be capable of delivering 30,000 kW of power to keep lighting installations, escalators, control and signaling systems and information systems 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. All this ensures that people are safely evacuated from the underground, after which the metro stations can be closed. To supply enough electrical power to each underground station, up to 2 MW is required pro service line. That not being enough to operate the trains themselves, these come to a standstill in the event of an outage, with only certain units staying operative to bring passengers to the next station for their safe evacuation.
"I have 100% faith in the engines"
Most engines installed in emergency gensets hardly ever need to go on stream. 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. To check that they're always operational, test runs are performed on a monthly basis, giving the engines the opportunity for a few hours to show their capabilities. “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.” And if there does happen to be a hitch at one of the gensets, the others can switch in, since all six are connected. In other words, if one generator set fails or is being serviced, the others can come on stream.
All of which means that the Vienna metro's many passengers can relax in the knowledge that they will always be able to exit the underground safely should the mains power be disrupted.