A Simple Algorithm to Assess the Speed Stability of Induction Generators

Problem statement: The speed stability if Induction Generators (IG) can be defined as its ability to remain connected to the electric network, operating at a mechanical speed close to the speed associated to the actual system frequency, after being subjected to a perturbation. This IG behavior is normally studied using dynamical methods that are determined through time-consuming simulations and are difficult to implement in simpler computational devices, such as microcontrollers, that are the basic component of electronic protection relays. In this way, the possibility to assess the speed stability of IGs through a simpler method becomes very desirable. Approach: This paper proposes a simple analytical method for assessing the speed stability of induction generators connected to distribution systems that can be easily implemented in microcontrollers, based on the determination of its critical speed and critical time. The formulation of the proposed method is founded on the electricalmechanical equilibrium equations associated to the steady-state operation condition in the classical induction machine model. Results: The developed method has four simple steps, based on mathematical equations obtained from the classical IG model and presented a mean difference less than 5% when compared with results obtained by dynamical simulations, tested in the context of a distribution electrical network that considers generator parameters, line parameters and capacitor bank variation. Conclusions/Recommendations: This analytical approach can be used as a guide to significantly reduce the simulation efforts, required to assess the induction generators stability in distribution networks and permits its implementation in less complex computational contexts, like microcontrollers. The reliability of the method has been attested by extensive simulation results.