Chessington World of Adventures, a popular theme park and zoo in south-west London, offers 25 different rides and attractions. One of the most famous attractions is the Vampire ride. It became the UK’s first suspended roller coaster when it opened in 1990 and the only coaster to fly above tree height. During the summer season, the Vampire now thrills adrenalin junkies of all ages – it is one of thefew rollercoasters Europe-wide available also for small children, starting at a height of 1.1m. At peak periods, the Vampire ride attracts 17,000 visitors a day.
Three trains make, on average, 720 laps ofthe track over an eight-hour day. This createsa substantial workload for the ride’s DC motor control system. The ageing control system was becoming costly in both maintenance and downtime. Chessington World of Adventures needed to improve the ride’s reliability ahead of the summer’s peak-season.
Chessington World of Adventures had two options: Redesign the control system to useAC motors and AC drives, or keep the existing DC motor control system and retrofit it with modern DC drives. Redesigning with AC technology would mean a lengthy andcostly Health and Safety review. Keeping the already installed and proven DC technology proved both easier and more cost effective.
System integrator B & G Controls of Sittingbourne, Kent, was contracted by Chessington World of Adventures due to their knowledge of fair ground applications. B & G Controls chose DC drives from Sprint Electric because they had previously worked together on another demanding ride application at Chessington World of Adventures.
David Garwood from B & G Controls explains,“Two 430 Ampere PLX digital DC drives were installed to control the Vampire’s flight. Each flight has many twists and high-speed turns, but the two lifts create the serious demand. To raise the three trains and 24 passengers, the drives operate at 90 percent current for the first lift and 100 percent current for the second.”
To make the ride’s load-run-disembark process a smooth one for the park’s visitors, the PLX has to interface with an existing SLC-500 series PLC from Allen Bradley. “The PLX DCdrives’ software made it possible to re-program inside the drive, some of the signals coming out of the PLC to suit the application better. Signals such as Field o.k. and Tacho o.k. required logic function and timer function PLX application blocks to re-create whatthe PLC needed of them,” explains Sprint Electric’s research and development director Aris Potamianos, who helped with the software integration and commissioning.
Other PLX safety features ideally suited to this application are the drive’s coast-stop input and the ability to revert automatically from tacho generator speed feedback to armature voltage feedback. The PLX’s coast-stop inputensures the ride control can effect an almost instant isolation of the drive from the rest of the process in the unlikely scenario of hardware or software failure inside the PLX. The coast-stop input forces the drive to cease supplying armature current to the motor irrespective of drive operating conditions.
Another useful safety feature is the PLX’s abilityto automatically reveart from tacho generator speed feedback to armature voltage feedback in case of mechanical or electrical damage to the tacho generator or its connection medium to the drive. The drive willgive a warning of this failure to the PLC but itwill continue to be under closed loop speed control until the next convenient stop instance when the fault can be attended to.
With the installation and commissioning complete, Chessington World of Adventures’engineers are pleased with the re-vamped control system, having noticed the ramp upto full speed is a lot smoother now. David Garwood concludes, “The test runs during the park’s closed season were really successful.We were all looking forward to seeingthe improvements when the park openedagain in the summer.” Excited young visitors’comments on the Chessington website giveevidence that the refurbishment of the Vampireride was a success: “One of the best ridesever! Great for all ages; my cousins aged fiveand seven loved it,” says a girl. “This is probably the most exhilarating ride in the wholepark – amazing,” comments a boy. And another visitor adds, “Can’t wait to go on it again next year!”
Increase in accuracy and productivity as well as lower energy consumption make these DC drives ideal for retrofits when a more effective, modern drive system is required.Sprint Electric offers a full range of PLX digital DC drives from 12 Amps up to 2250 Amps,with all models available from stock. Whether in retrofits or original equipment, the DC Drives are being used in many different applicationsincluding metal processing, the pulp and paper industry, rubber and plastic processing, lifting equipment, food processing, leisure industries and many more.
