Investigation of the Voltage sag pattern in Tanesco power networks at Tegeta grid substation in Dar es Salaam Region

TANESCO is suffering from revenue losses, damaged network equipment’s and complaints from customers due to poor power quality. One of the most significant elements of poor power quality is voltage sag disturbances .The main objective of this study is to explore and investigate voltage sag patterns in TANESCO power networks at Tegeta Grid Substation in Dar es Salaam Region. To achieve the main objective, the NRS-2:1996 standard ranging from 44 kV to 132 kV inclusively with voltage sag per annum of 16, 25, 25, 80 and 120 for sag type Z, T, S, X and Y respectively is adopted as a reference. A personal computer installed with PQRM software was used to retrieve the monthly data from impedo graph connected to the 132 kV power network. The data were sorted and counted using count if command in Microsoft Excel. The annual data with voltage sag per annum of 79, 1, 24, 4 and 250 for sag type Z, T, S, X and Y respectively, were obtained by combining the monthly data. The comparison with the adopted standard was made by computing the deviation and percentage error. The result showed that the sag category Y and Z had higher frequency of occurrence and deviated from the adopted standard by 130 and 63 and percentage error of 108.3% and 393.7% respectively ; while other types of sag were within the standard. Furthermore, the relationship between voltage sag and the connected load was established and the relation showed that, from 06.00 am to 08.00 pm the voltage sag profile followed the same pattern while in the remaining hours there was no relationship. The sag pattern was further explored and showed that, all types of voltage sag followed the same pattern throughout the year.