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Have You Been Told Your Drive Is Obsolete?

(MARCH 2015)

Have you been told your drive is obsolete?


We often find clients come to us with drives they have been told are no longer in production and as a result are obsolete and no longer supported. We find that this is rarely the case.

One of our clients came to us with just such a problem, the drive, an Allen Bradley 1336, 250kVA large inverter had failed, and due to the age of this drive they were unable to have the drive repaired by the OEM who could only offer an expensive substitute.


This comes with two problems, first the obvious expense for a drive of this size, and also the additional problem of modifying the control system to be compatible with the new equivalent; the drive being used in a complex pumping application.


Once we had spoken with our client we arranged same-day collection, and the clients engineers had the drive waiting for our courier. Upon inspection in our workshop it was found that the unit had suffered catastrophic failure of the main bus capacitor bank as we have found with several drive models in this range.


The Caps had failed and spilled electrolyte throughout the unit causing the failure of the mains rectification circuit, this also led to high voltage breaching the IGBT gate isolation and reaching the low voltage control sections.


We knew it would be impossible to assess the failure and the root cause accurately until we had repaired the capacitor bank and power stages to allow load testing as part of our Test – diagnose – Test – Repair approach, ensuring drives work when returned to service, and maintaining our exceptional levels of reliability.


Due to the age of the unit many of the parts for this drive were themselves obsolete so spares had to be sourced from specialist suppliers in both America and the Far East to allow testing to be carried out, and an accurate diagnosis to be made.


Once the replacement capacitors had been fitted our engineers tested the drive to check performance, this testing revealed the drive had suffered additional damage to both the gate driver card and CPU control card as part of the initial failure.


These components more specialised due to presence of items such as hybrid I.C.s, and programmable logic I.C.s, and for many their scarcity would have made tracking them down a very difficult task, however thanks to our longstanding relationships with a network of suppliers worldwide we were able to source these parts and place orders within hours.


On arrival at our workshop, the components were fitted to the drive. This process required our engineers to access our extensive data base of drive specifications and parameters to ensure the panels were configured correctly for the make and model of drive.


Once reassembled we used our in house dynamometer to load and soak test the drive, a process we believe is essential for a drive of this capacity, this proved to be a very valuable process as it revealed a problem when running under load that pointed to the new capacitors in the load bank being faulty, this was confirmed by further testing.


As a result we removed and disposed of the capacitors, and  informed our supplier of the issue for our internal QA procedure,  we then  went to an alternative supplier to ensure the issue did not occur a second time. Once the capacitors were replaced we retested the drive which performed correctly throughout. The drive has now been dispatched to the client for installation.


This project clearly demonstrates the value of the test – diagnose – repair- test  strategy , without this process the capacitors may have failed on installation resulting in additional downtime for the client, which at one of the UKs largest power stati

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