Intermittent ‘turn-on/off’ faults repeatedly resulting in isolation.
The Problem
- In 2010 equipment was showing intermittent ‘turn-on/off’ faults repeatedly resulting in isolation. This had become a long standing problem.
- Equipment was being returned to the OEM, only to be returned ‘NFF’, despite the fault continuing to be present when returned to service
- Issue was compounded by 12 week lead time for repair, resulting in sets running without a full complement of working inverters
Investigation
- 2 weeks of intensive reverse engineering and tests led to discovery of the root cause:
- Degrading internal connection within IGBT, leading to false error detection
Solution
- Custom test devised to detect the issue at an early stage
- Failing IGBTs replaced with alternative batch
- SET took over repair from OEM
RESULT
- NFF rate dropped to near zero. The problem was being found and corrected
- Lead times reduced to typically 2 weeks
- Sets were running with full compliment of working inverters
- This and other work contributed to the Silver Spanner Award for most improved fleet
