Dynamic Performance of Doubly Fed Hydroelectric Machines under Voltage Unbalance - A Relative Electrothermomechanical Analysis

Abstract

Deployment of renewable energy sources in power grid causes an undesirable characteristic in the voltage profile due to its stochastic nature. Such electrical perturbations may impact the performance of equipment or machines connected to the grid, especially large rated machines (e.g., 250 MW). This paper investigates the electrical, thermal, and mechanical stresses on large rated doubly fed synchronous (fixed speed) and doubly fed asynchronous (variable speed) machines used in pumped storage power plants under voltage unbalance. Also, the lifespan of the drive train considering thermal stress is estimated. In this paper, considering the medium voltage distribution system (15.75 kV), the magnitude of voltage unbalance is opted as 2.5% and 5% to test the performance of doubly fed machines. With respect to these considerations, the impacts on machine parameters such as rotor current, stator current, input power, torque, and losses are comprehensively investigated. To observe the performance of large rated doubly fed machine drive system under voltage unbalances, the MATLAB/Simulink environment is adopted. Also, to realize the real-time impact on doubly fed machines, a prototype rig (with 2.2-kW synchronous and asynchronous machines) are experimented. The practical significance of this relative analysis is to minimize voltage collapse in the system and for developing the robust system with countermeasures. © 1972-2012 IEEE.