MODELLING STEADY STATE AND TRANSIENT STABILITY PARAMETERS FOR KAINJI HYDROPOWER STATION, NIGERIA

Abstract

In Nigeria, total installed power generation capacity exceeds 10,000MW with the hydro plants contributing 30% of the total available capacity and about 14.5% of total installed capacity. Kainji Hydro Power Plant (KHPP) built in December 1968 is the premier power plant in Nigeria located about 102 km upstream of Jebba Hydro Power Plant (JHPP) with eight sets of Kaplan turbines totaling 760MW of generation capacity installed. However, for over two decades, its stability and that of the entire grid system has dwindled due to neglect, faults and incessant collapse of the grid system. Therefore, it has become necessary to model and simulate the stability parameters of Kainji HPP to improve its operational stability and that of the entire grid system. The main objectives of this research are, to develop a simulation model for Kainji Hydro Power Plant (KHPP) using MATLAB/Simulink software; and evaluate the steady-state and transient stability parameters for Kainji HPP. The simulation model was developed using Matlab/Simulink software. The model comprises of eight generating unit reference models and each reference model consists of the hydraulic turbine governor (Proportional Integral Derivative PID, servomotor and turbine), synchronous generator and an excitation system. The turbine governor, excitation systems, and synchronous machine blocks from SIMULINK/Matlab library were configured using data obtained from Kainji HPP documentation. A three-phase line circuit breaker was used to implement the dynamic loading of the system by varying the additional load from 10MW to 60 MW at a predetermined time t is 5.2 s in each case. The steady state and transient responses of the system to a variable load increase and three- phase short circuit fault applied at 5.2 sec and cleared at 5.4 sec were studied. From the simulation results, steady state stability limits of load angle 85 0, terminal voltage 0.68 pu, virotor speed 1.21 pu, excitation voltage 1.30 pu, and stator current 7.2 pu were established. Similarly, transient stability limits of load angle 170 0 , terminal voltage 0.60 pu, rotor speed 1.05 pu, excitation voltage 1.25 pu, and stator current 7.1 pu were also determined for Kainji HPP. The results show that the terminal voltage quickly regained stability at the removal of the fault; the load angle was steady at 18 0 , before the introduction of fault at time t is 5.2 s and both the stator current and excitation voltage were transiently stable after the fault was cleared at 5.4 s at a critical clearing time of 0.2 s but oscillated heavily and transiently unstable at a critical clearing time of 0.4 s. The rotor speed oscillated during the fault which is due to slow governor action and the load angle δ surge to 170 0 during the transient fault and became transiently stable at δ is 25 0 . The simulation results obtained at a critical clearing time of 0.4s were transiently unstable due to continuous oscillations after the fault was cleared at time t is 5.4 s. However, the simulation result shows tremendous improvement in the stability of Kainji HPP at a critical clearing time of 0.2 s which will enhance its operational efficiency and reduction in total system outages in the grid.