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Sometimes, it isn’t that straightforward…

Although replacing inverters rather than repairing them is sometimes the favoured option, it isn’t always as easy as it might appear.

On many early drives there was little or no industry standard interfacing, leading to rather bespoke, specialised control systems. This is not necessarily a problem until control engineers are tasked with retrofitting the existing system with a modern inverter A large print works asked NDC if they could offer a replacement system for a number of Black Clawson variable speed AC drives. The 180kW pump drives were in use 24/7 which meant that replacing the units with new, reliable drives was the most obvious route to take. However, once a site survey had been undertaken, it became very apparent that retrofitting the drives was a massive task. During the construction of the building the drives had been winched into the plant rooms and then bricked up, each plant room had two spare drives, but these had long since failed. The price to replace the drives was prohibitively high, so NDC offered the customer another route. NDC offered to maintain the drives, repair the faulty spare drives and even source and store all spares, until such time that the funds were available to replace with new. The customer was sceptical at first, citing the manufacturers opinion that “no one could support this old stuff anymore”. As the drives could not be removed, on-site testing of faulty drives was essential to identify faults, NDC engineers then repaired some fault on-site, while pcb faults were rectified in the lab and then tested using bespoke test rigs for each card. Although the process took over one month, all spare drives were returned to service, and the task of overhauling and refurbishing each drive began. As a result of this rather unusual approach, the incidence of pump stoppages has fallen from an average of six per week to one or two per month.

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