Driving the Al Hoota cave train

The Al Hoota cave is a major tourist attraction in Oman, receiving thousands of visitors a year. The operators of the cave needed a transport system that would take visitors a distance of over half a kilometre from the visitor centre to the cave in comfort and safety.

Severn-Lamb, a manufacturer of specialised vehicles and people movers based in Warwickshire, was appointed to come up with a suitable means of transport. The operators specified an energy efficient system and one that was also quiet running so it didn't spoil the visitor experience or disturb the one hundred or more species of wildlife that live in the cave system. Electric propulsion was the only practical solution to meet these requirements, so the next step was to find a propulsion supplier that was both reputable and had an international presence with regards to warranty and support.

That supplier turned out to be ABB Drives Alliance member, Sentridge Control, who supplied four ABB ACS 800 industrial drives, each of 30kW and four ABB high-efficiency 37kW motors to power the train. The two companies set about designing a suitable propulsion system for a 700 metre-long track ride - some 100 metres of which would be within the cave itself. It also had to be capable of carrying 48 passengers, travelling at up to 20km/h and taking power from a three-phase, 415V electrified third rail arrangement.

According to Glen Hickman of Sentridge Control, the drive design included provision for dual redundancy, so that if one motor was lost for any reason, the train could continue on its journey. Another useful feature highlighted by Mr Hickman is the built-in drive-to-drive link, which allows the drives to talk to each other via a master-follower arrangement, enabling them to run at the same speed and share the load.

The drives allow the train to be driven from either end by transferring the master drive function to the rearmost drive. Another feature that could be used in the future is the ability for the drives to receive a signal from an external pick-up mounted on the train, allowing them to detect points and reduce speed accordingly. And with ambient temperatures climbing to 50°C, cooling air for the drives is obtained from the main cab air conditioning system. Severn-Lamb engineering director, Greg Squires summarises:

“We were very impressed with the on-site support provided by ABB, which we needed to call on a couple of times. Flying engineers out to the area is expensive, so the ability to use ABB’s local engineers was a real benefit for us when commissioning the system.”