Meissner recently completed a project in which it was appointed by Eskom to supply uninterruptible power supplies (UPSs) to the power utility’s Megawatt Park facility. The project involved the replacement of 4 x 400 kVA UPSs and their associated control panels with the latest Powerware UPSs offering parallel redundancy.

In a congratulatory letter to Meissner on the successful completion of the project, Robert Twigg, technical services manager, Eskom stated, "I am impressed to the extent that in my opinion Meissner Uninterruptible Power should be 'rubber stamped' as the leaders in this industry and I will undoubtedly recommend your team to other organisations. The project was undertaken during the recent load shedding period which added a number of unforeseen circumstances that the Meissner installation team handled in an exemplary manner."

Abel Martins (left) of Meissner and Robert Twigg of Eskom

To complicate matters, Eskom was very keen to retain its existing open cell vented batteries as they had only been replaced some five years previously and still had another 10 to 12 years of life expectancy. This posed a slight dilemma, as the DC voltages of the old system were not compatible with the new technology and this meant that either the new UPSs had to be modified or alternatively Eskom faced the necessity of additional new batteries.

Two challenges arose - firstly, that there was not enough space to accommodate the cells required - and secondly, that new batteries mixed with older cells do not represent an ideal DC mix. Meissner came up with an alternative to supply three larger 500 kVA UPSs, and then in order to attain the correct DC voltage level, to split one of the existing four sets of wet cells into three parts and to add one of those three parts to each of the remaining three battery sets. This resulted in exactly the correct DC voltage as required by each of the new 500 kVA UPSs. Certainly, Eskom would be sacrificing 100 kVA in total UPS power but the load had reduced over the years anyway down to only 830 kVA.

Part of the new UPS installation necessitated the upgrade and refurbishment of the existing UPS supply breakers and their control system. Along with the new UPSs, new maintenance bypass switchgear was also required, all of which resulted in a colossal AC re-cabling job that was to be carried out at the same time as the DC reconfiguration. In addition to this, the IT department at Megawatt Park announced that it could not afford the 24 to 36 hours of downtime required for a once-off load cut-over from the old UPSs to new ones.

In order to facilitate this, Meissner loaned Eskom a fourth 500 kVA UPS and, courtesy of Battery Technologies, two full sets of sealed lead-acid maintenance-free batteries to back up two of the new 500 kVA UPSs which would be installed in a separate room next to the actual UPS room. This allowed the load to be seamlessly connected to and supported by the two temporarily installed parallel 500 kVAs while the old 400 kVA machines were removed from their positions.

The other two new 500 kVA UPSs were then installed in their intended positions in the UPS room, the DC voltages of the existing wet cells were configured and their associated DC protection gear was installed. At the same time CHI Control, Meissner's sister company, completed the task of refurbishing the UPS supply AC breakers. When all was complete, the load was again transferred to the two new UPSs, now in their permanent positions. The two temporary UPSs could then be disconnected and one of them then moved from its temporary position and installed permanently in the UPS room alongside the other two new 500 kVA units.

The end result is that Eskom now has a perfectly configured N+1 parallel redundant UPS system in place to cater for power outages somewhat longer than those envisioned in the past.