Determination of dstatcom parameters for a 33 kv line from Shinyanga to Bariadi

Voltage drop on electric power distribution feeders increases with feeder length as applies to the 33 kV line from Shinyanga to Bariadi that runs over 180 km distance with no compensators installed at the receiving end. The voltage received at the end of feeder experience large voltage drop resulting to motors for water pumping connected near the end of feeder failing to start during peak load. Line constants were represented in nominal π model. DSTATCOM capacitive and inductive dynamic ranges of -1900 kVAR and +1900 kVAR respectively were evaluated based on the system fault level value while the dc capacitor value of 0.19 mF was obtained by using the energy storage for five cycles. The DSTATCOM model used three levels VSC that was synthesized with a Neutral Point Clamped configuration. The synchronous reference frame strategy using modified Park transformation matrix was applied in the control part of the VSC in order to produce PWM pulse for switching the GTOs. MATLAB/Simulink was applied to simulate the feeder model and the DSTATCOM model for different loading conditions in order to evaluate the steady state performance of DSTATCOM. Simulation results revealed that, for the load of 3.4 MW, before and after application DSTATCOM, the receiving end voltage was 30.75 kV and 32.4 kV respectively. For light load of 300 kW, before and after application DSTATCOM, the receiving end voltage was 46 kV and 33kV respectively. In the frequency domain analysis of the system, the gain margin was infinity implying that the system was inherently stable. The Nyquist plot had no encirclement of the -1 point. It can be concluded that, the proposed DSTATCOM was capable of controlling both the voltage drop and voltage rise of the feeder to acceptable practical values.