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07/04/2011
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Chester Zoo is reporting improved performance from its newly refurbished 1.5km long straddle beam monorail system – in large part due to new Parker drives and ac motors.
 The zoo's original system was installed 17 years ago and, although extended and upgraded, it has, until recently, retained much of the original control and motion technology, including heavy-duty dc motors.
"The original power, drive and control systems had been custom built by a local specialist," says project coordinator, Paul Curtis. "But, with his recent retirement we lost a significant degree of knowledge.
"Just as importantly, the systems had reached the point where they were becoming increasingly unreliable and expensive to maintain. They were also inefficient, in terms of energy consumption, relatively noisy and it was difficult to ensure a smooth ride."
Curtis explains that the refurbishment – carried out by Stockport-based systems integrator T&M Machine Tools – involved overhauling everything from the track to the control systems. In particular, the dc motors were replaced with ac equivalents, while Parker AC890 variable speed drives were introduced to control and balance motor speeds.
Each carriage has now been fitted with two 2.2kW ac motors, controlled by a network of eight drives – one acting as master, the others slaves, with increasing numbers switched on or off, in line with energy demands.
The drive network also now communicates with a PLC on each train, and hence also with the central control and traffic management system – with communications enhanced by FireWire. There is also onboard Ethernet, for remote diagnostics and programming. Remote monitoring is carried out over a 5GHz wireless grid.
"The master/slave configuration is important, as the ability to introduce additional drives as demand increases enables us to maintain constant speeds – for example, as passenger loads change or as trains traverse different gradients," comments Curtis.
"Greater control also enables us to reduce energy consumption and gives us the option of safely increasing train speeds," he adds.
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Author
Brian Tinham
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