Investigation of harmonic distortion on Dar es Salaam 132KV network

In this study investigation and assessment of measured voltage and current waveforms in the regard of harmonic distortion on 132kv TANESCO network in Dar es Salaam region is presented. Measurements were performed by a power quality monitoring equipment (pedograph) having 16 bit resolution and sampling rate of 128 samples per cycle. Assessment were performed using a power quality analysis package- power quality recorder manager (PQRM). The result show that while individual total harmonics distortion were within the limit of compatibility level, fifth and fifteenth harmonics were above the compatibility level set by IEC. The maximum THD value obtained from the network also exceed the value recommended by IEC and IEEE standards for electromagnetic compatibility. The voltage unbalance trend varied from minimum of 1% up to the maximum 10%. The study reveals a significant unbalance in not linear load connected to the downstream of the network. Also, the current unbalance was noted varying from 46.4% to 50.3%, the situation which predict significant load imbalances to the downstream of the network. The impact of harmonic on the connected equipment (I,e power transformers) was also investigated and the extent of de-rating the equipment capacity was established to be 92% of the nameplate rating. It is therefore recommended for the new transformers to be connected to the network to be k-rated transformers so that copper losses and iron losses are optimized and efficiency increased. In order for existing transformers to handle additional harmonic currents resulting from nonlinear loads, their capacity must be de-rated by 92% of the nameplate rating to avoid overheating or pre-mature failure.