Drives refurbishment completes at UPM Shotton paper mill 07 March 2011

UPM Shotton Paper's recycled fibre plant reports that its extensive low voltage ac drive refurbishment programme has been successfully completed, and that uptime has been massively improved.

The work was carried out by ABB on a series of drives used throughout this critical plant, which feeds the main paper machines producing more than 500,000 tonnes of newsprint per annum.

Ray von der Fecht, head of UPM Shotton's automation team, explains that the refurbishment programme was instigated to improve the overall performance of the plant's installed drives base – so reducing downtime and cuttintg the cost of repairs.

ABB was tasked with identifying reasons for the existing low voltage ac drives downtime, and von der Fecht says that, at first, there were concerns that the power supply network may be causing spurious spikes that were, in turn, damaging the drives' semiconductors.

Engineers from ABB in Sweden applied a network analysis tool to look at the 11kV feeds to the 690V motor control centres feeding the drives, before confirming that the network was stable – so eliminating this potential cause.

Having visited ABB's drives centre in Helsinki, von der Fecht says ABB provided valuable guidance for the project. "After very constructive discussions, it was agreed that the next failure would be returned to the factory for a full analysis," he explains.

In the event, the drives were suffering from dry solder joints on the power semiconductor units. Although this was natural degradation and a common occurrence with drives generally, it was happening outside of normal warranty. However, von der Fecht says ABB offered to support UPM with replacement units.

"We learned a lot from just speaking with ABB's technical experts. There are very few companies that we could ever get that close to – where you can speak to the designers, with openness and honesty [and] directly contact the people that know the product intimately."

Using ABB's service workshop at St Neots, Cambridgeshire, the refurbishment, phased in over six months, included replacing power semiconductor modules and fans in 36 drives, ranging from 160kW to 560kW.

ABB worked on four drives at a time, also supplying standby drives to cover those being refurbished. Each drive was upgraded in a day and the batch tested and returned to the Shotton site the following week.

"Due to process changes, the focus on the plant is much more intense, especially as [it] has fewer shutdowns. The refurbishment program was done in a timely manner ahead of this more demanding availability requirement," says Steve Thomson, area automation supervisor.

"We are extremely pleased with ABB's response," says von der Fecht. "Since the refurbishment we have seen a marked increase in the reliability of the drives installation which helps overcome excessive downtime and the high cost of repairs we were experiencing previously."

Brian Tinham

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