Softstart UK hammers motor starter costs for EdF
1 min read
When EdF (Cottam Power) needed a starter for the MV drive fitted to a hammer mill at its Nottingham site, most suppliers claimed that only a variable speed drive would be suitable.
Softstart UK, however, offered a cheaper MV soft starter that Graham Wolsey, an engineer on the EdF project team, reports has proved entirely satisfactory, also allowing the firm to save thousands of pounds on the project budget.
The equipment was installed at EdF's Nottingham site, adjacent to Cottam Power Station, where the company pulverises olive cake and mixes it with coke to form an environmentally friendly biofuel, burned in the power station.
The hammer mill receives olive cake via a triple screw feeder at up to 30 tonnes per hour, and is driven by a 350kW 3.3kV electric motor. The drum, with its hammers attached, has very high inertia and takes up to 15 seconds at start up to reach operating speed at 3,000 rpm.
Hence conventional direct-on-line starting was not possible, because the very high torque would be likely to damage the drive system couplings system.
Wolsey says that when EdF engineers approached MV drive systems suppliers, most said that a VSD was the only feasible solution, and that a soft starter as would be unable to provide consistently accurate starting control.
Softstart UK disagreed and a PLC-controlled unit from its MV-DS range was selected. Interconnections in the MV section use MV cable, making them lighter and eliminating the need for costly partial discharge testing.
In addition, the MV section is isolated from the control section by a fibre optic link for gate firing control. MV-DS soft starters also incorporate line contactors that use vacuum switching, which combines reliability and long life with zero maintenance.
"These characteristics seemed to make the MV-DS an excellent match for our needs," states Wolsey, "but after the dire warnings we'd received about using soft starters, there was still a certain amount of tension when we hit the start button for the first time."
But he adds: "We needn't have worried, as the advice provided was every bit as good as the company's products, and the mill performed exactly as we wanted."
The mill is now in daily use and the soft starter is performing faultlessly. Currently, it is only called upon to perform one start per day, but Wolsey says it has been demonstrated as being capable of handling up to four starts per hour."
"I would have absolutely no hesitation in recommending [Softstart UK] to anyone who has unusual and challenging starting requirements," concludes Wolsey.
