At Chelker Raw Water Pumping Station we were asked to look at asset replacing obsolete medium voltage speed regulators with new low voltage inverters this would allow the old Medium Voltage motors to be replaced as they regularly broke down and were becoming difficult to repair as parts were unavailable.

The original challenge was to see if we could get a new LV drive and a 3300/400V transformer in the original space for the regulator. On paper this looked feasible but there were technical and specification issues to resolve. Because we had been involved early by the contractor we were able to visit the site and discuss the various issues. Although the original solution looked good on paper we quickly found some problems. There were issues with specification compliance as the transformers were not the YW preferred solution and it was quickly found that the old 3.3kV switchgear was unsuitable for feeding the new equipment. This was a major problem as the switchgear was obsolete and at the end of its asset life. There was no money on the scheme for replacing it.

We then suggested that instead of supplying four 3300/690V transformers we could replace the upstream transformers with two new 11000/690V units and therefore bypass the redundant switchgear. A new LV board could be fitted instead. This was still more expensive but was much cheaper than replacing the MV switchboard.

We continued to look at the site and discovered that the new LV board could not be installed while the existing MV Board was in situ. We asked if there was any reason why it had to be there and suggested that it could be in the pump room with the inverters. This was acceptable to all and also reduced the site cabling as the cable runs were shorter.

At this point we realised that we could incorporate the inverters into the switchboard as a conventional MCC. This saved having additional switchgear and site cabling. It also worked out to be the cheaper solution as it reduced the switchgear costs and cable installation costs. The main benefit was that we were able to remove all of the obsolete and unreliable MV equipment within the original budget. If we had not had the early involvement there was a possibility that the whole scheme would have been put back until AMP6 when the MV switchgear was due for replacement and the site would have become very unreliable.