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Fault Analysis Gives NDC the Edge

(December 2010) Jost Luffer Crane

NDC fully understands the importance of a thorough engineering investigation when repairing drives for complex lifting applications.

When recently asked to repair a fault on a Leroy Somer SP4402 inverter from a Jost Luffer Crane our exhaustive processes were put to the test. The crane operator delivered the unit from site to our South East Service Centre for an immediate assessment, concerned to minimize expensive downtime. Initially, the drive appeared to work perfectly well and showed no sign of the customer's reported fault (which was that the jib would raise, but not lower).

Given the customer's fault report, NDC engineers pressed on and resolved to investigate further and mimic the cranes own control by using drawings and parameter sets recorded from previous repairs on identical cranes. Many of our competitors would at that point have simply returned the unit unrepaired to the customer, declaring 'no fault found'.
However, our inspection and testing processes finally determined that one of the digital inputs was not being interpreted correctly, and therefore failing to operate the crane correctly - although basic testing showed the inverter to be fully operational.

To effect the repair it was then necessary to swap the SM-Application module with an identical unit with the correct programme, this then proved that the parameters within the drive unit itself had corrupted.
We then decided to re-programme with a known good file set from our own internal library of crane specific inverters (which includes Control Techniques, Leroy Somer, Lenze, SSD, Reliance, Telemecanique, SEW, Loher, Omron, Yaskawa and others).

The drive was finally re-tested and proven to operate as per the drawing schematic. To ensure the crane was then fully safe to use, the manufacturer e-mailed the correct set of crane-specific parameters over to us and the crane was returned to full use that afternoon.

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