Today I had the privilege to design some electric power delivery systems to supply Northern Region Water Board (NRWB) under their Karonga Town Water Supply Project, funded by The Department for International Development (DFID). I therefore visited their sites at Mlare, Balyenge (Mwenilondo), Bwiba, Nyanja Hills and Karonga Water Treatment Plant.
While at Mwenilondo, I was in the bush capturing geo-spatial data using a mobile mapper. Unfortunately I encountered some overzealous wasps and received multiple stings on my neck, just behind the left ear. I had to endure the pain without rubbing the affected area, as doing the same was multiplying it further a thousand fold. When I came out to the open where the two colleagues from NRWB were waiting, I was advised to apply some Colgate paste to ease the pain. I reluctantly obliged and played along. Fortunately my field kit had some toiletries as I was yet to check-in at my place of lodging.
One of the places had a power requirement of 1,322KW, which translates to 1,652.5KVA at the applicants power factor of 0.8 in-line with their Consultants (Note that our country's recommended p.f. is 0.85. Currently, the site is supplied by a 500KVA, 11/0.4KV, ONAN, Dyn11, Ground Mounted (GM) Transformer, which is fed by a 70sq.mm 3 core Cross-linked polyethylene (XLPE) copper cable on the primary side and a 300sq.mm single core copper armoured cable on the secondary side. According to our work procedures, this capacity requirement has to be referred to our System Planning counterparts to carry out load flow simulations of the whole distribution feeder for such a load. However, in order to deliver the requested power and to be in tandem with the transformer capacity standardisation of the employer, the probable transformer choice is 2,000KVA, 11/0.4KV GM Transformer. This choice gives us 104.97A primary and 2,886.75A secondary currents respectively. This may eventually culminate into issues of cable sizing and market availability. Another choice, therefore, would be to split the loading onto two sets of 1,000KVA each.
