This paper describes two new models for wind turbine generating systems (WTGSs), widely used as distributed generation sources in distribution systems. These models are developed by using the modifications of bi-quadratic equation which is generally used for the calculation of node voltages in distribution systems' load flow analysis. The developed models are validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover, and with the calculated values obtained by using the other models reported in the literature. They are also incorporated into distribution systems' load flow analysis, and the results are compared with the results of their Simulink models. Simulink models are developed in Matlab using SimPowerSystems Blockset. (C) 2009 Elsevier Ltd. All rights reserved.