Static voltage stability assessment of Nairobi area power distribution network

Abstract

Voltage instability is a problem of overloaded systems. The main factor causing voltage instability is the inability of the power system to meet the demand for reactive power. The Nairobi Area Power distribution network supplies over 50% of Kenya’s national load demand. The increase in load demand in the network, over the years has generated interest to the network’s voltage stability status. This research assessed the voltage stability of Nairobi Area Power distribution network using static analyses methods. The objectives of the study were to identify the voltage weak buses and overloaded branches in the network, and to assess the network proximity to voltage collapse point. The network power flow problem was formulated, and solution attained using Newton Raphson method to determine the base operating voltages and angles, the power flows, and to compute the full Jacobian matrix. Sensitivity and modal analyses methods were then used to investigate the network weak buses and overloaded branches. Further P-V and Q-V curves analysis methods were used to compute the active and reactive power margins respectively of the identified weak buses.The peak load conditions of June, 2012 were used in the case study. The study established that the network isoperating closer to voltagestabilitylimit at peak load conditions. Further analysis is recommended on thebuses identified as weak to investigate the impact of reactive power compensation, and contingency analysis for the network branches identified as overload to study the impact of loss of any of those branches. Finally, since the loading and network topology of the distribution networks are known to change relatively fast, it is recommended that voltage stability analysis be conducted at regulartime intervals to determine the stability status of the network as the topology and loadings change.