Static Voltage Stability Assessment of the Kenyan Power Network

Abstract

In recent years, the Kenyan Power Network has witnessed large growths in load demand. Although the increased load demand has somewhat been matched with an increase in transmission and generation capacity, the rate of expansion has not been matched with the rate of increase in load demand due to economic, environmental, and geographical constraints. This has led to the system being prone to instability since it is being operated under stressed conditions. In the recent past, several studies have been carried out on voltage stability analysis and improvement using various conventional methods. However, conventional methods have various limitations in their utilization for voltage stability analysis. One solution to overcome these limitations is to employ a combination of one or more methods so as to get more information and greater degree of accuracy in voltage stability studies. In this paper, a methodology is proposed involving the combination of QV modal analysis, sensitivity analysis (VQ) and power-voltage curves in assessing the static voltage stability analysis taking a case study of the Kenyan Power Network. V-Q sensitivity analysis and QV modal analysis have been used to identify the load regions most susceptible to voltage instability and the corresponding weak buses in the network for various V-Q responses. Reactive power loss sensitivities for branches in the network have been used to determine the critical (weak) lines in the network. Loading margins (LM) and voltage stability margins (VSM) have then been used to determine the proximity to voltage collapse of the voltage weak buses identified by QV modal analysis. The effect of tripping one the critical lines on the voltage weak buses is also investigated. The current high voltage power network under the average peak loading conditions during the year 2019 is considered for the study. The paper also reviews existing voltage stability analysis methods and their limitations.

A general index for voltage stability assessment of power system

“…3 Also, to determine the stability margin, the Jacobian matrix has been proposed as a solution, but these methods are time-consuming due to the complexity of the Jacobin matrix calculations. 4,5 The proposed index in Reference 6 is obtained by calculating the magnitude of the Thevenin equivalent impedance to the load impedance ratio at each bus. The primary drawback of the proposed indices in References 4-6 is that these indices require the calculation of the Jacobian matrix and the bus impedance matrix, which may be singular or close to singular and may not be obtained for radial configuration distribution systems.…”

“…To tackle this problem, a continuous power flow method has been proposed 3 . Also, to determine the stability margin, the Jacobian matrix has been proposed as a solution, but these methods are time‐consuming due to the complexity of the Jacobin matrix calculations 4,5 . The proposed index in Reference 6 is obtained by calculating the magnitude of the Thevenin equivalent impedance to the load impedance ratio at each bus.…”

Impact Analysis of Distributed Solar Photovoltaic Power Generation System Integration on Power Grid Voltage Stability Using Static Techniques

“…On the contrary, voltage instability is the failure of system to sustain adequate voltages in all or some of its nodes when it is operating normally and following disturbances like progressive load rises or failures of critical lines or units of generating. It may also be caused by a mismatch between reactive power generation and demand, which happens when a power system cannot supply enough reactive power [6]. A considerable decrease in system voltage results from significant reactive power losses if corrective actions to stop voltage instability are not taken.…”

Voltage Stability Assessments and Their Improvement Using Optimal Placed Static Synchronous Compensator (STATCOM)

“…According to the de nition of [1,2], voltage stability is "the ability of a power system network to maintain steady state voltages in all buses before and after the network is being subjected to a disturbance from a given initial operating condition." Voltage stability is a subset of power system stability that deals with the bus voltage operational limitations before and after a disturbance.…”