Experimental study on isolated operation of hydro-turbine governing system of Lunzua hydropower station in Zambia

摘要

This paper focused on the stable operation and control strategy of the hydro-turbine governing system (HTGS) in an isolated-grid operation mode. The stable operation of a hydropower station in isolated-grid operation mode is important for the safe operation of a power system. A regional power grid can be isolated from a main grid due to factors such as natural disasters, grid failures, and human errors. The Lunzua hydropower station in Zambia is often forced to operate as an isolated grid. To ensure its safe and stable operation, we conducted isolated-grid regulation tests in conjunction with field testing of HTGS and determined the parameters of the HTGS for stable operation of the isolated grid. In the field test, we first set the no-load and initial parameters for the isolated-grid mode through the no-load disturbance tests. Through simulated isolated-grid operation tests, we verified and further tuned the initial parameters. Meanwhile, we propose a control strategy for the transition between large-grid and isolated-grid modes. Through operational tests, we determined the parameters for stable operation in isolated-grid mode. During testing, we found that the water flow inertia time constant Tw was too large and the inertial time constant Ta of the impulsive generator was too small, which resulted in a narrow stability range of proportional-integral-derivative (PID) controller parameters for isolated-grid operation. The governing stability for isolated-grid operation was thus sensitive to the PID parameters. Since the isolated-grid field operation test of the HTGS of the Lunzua hydropower station was completed in August 2016, the generator units have maintained safe and stable operation in large-grid and isolated-grid modes, which validated the isolated-grid operation parameters and control strategy for the transition between large-grid and isolated-grid modes as determined by our test method. The methods of field test and control strategies used for isolated-grid operation have important practical value for the isolated grid operation of hydropower stations. (c) 2021 Elsevier Ltd. All rights reserved.