Power cuts were the rule rather than the exception, and emergency diesel power had to be kept on standby so that tea production could continue at any moment. The existing system comprised three generators: 1 x 350kVA Iveco connected to a Newage alternator fitted with an MX341 AVR, and 2 x newer 400kVA Iveco connected to Mecc Alte spa alternators fitted with UVR6 regulators. Although the third set could supply power on its own, only two of the three sets could synchronise with one another. Synchronisation was carried out manually by first adjusting the speed and then engaging the contactors via a push button when the semi-automatic relay logic system permitted. In addition to being time-consuming, this process was rather complicated and prone to electrical tripping.
The facility needed to upgrade its control units to fully automatic DSE5510s. Most of the existing control cabling was removed, leaving only the current transformer (CT) and voltage monitoring equipment in place. Contactor status (generator auxiliary closed contact) and generator bus voltage circuits were added, and after three intensive working days the system was ready for testing. A pile of cables, the generating set control unit, the kW meter, the phase sequence relay, the synchronisation control relay and the ECT equipment sat in a corner of the engine room, probably never to see a volt or an amp again!
After a few fine adjustments here and there, the new system worked flawlessly! Nchima’s sister facility at Lujeri had also upgraded its power station to a system very similar to the one described above. Standby power has now become a reliable and easy-to-use system; furthermore, thanks to the better use of the existing kW and kVA capacities, savings are also being made on engine running hours and fuel.
