The During last decades, Self-excited induction generators (SEIGs) are considered one of the devices which are using in manufacturing wind turbines. The generated power of these turbines depends on many manufacturing factors. The value of excitation capacitor is one of these important factors. This capacitor plays an effective role in self-excitation, and building voltage in addition to voltage regulation. In this paper a new reliable and accurate method for slip control and voltage build based on the steady-state equivalent circuit model, (nodal admittance technique) is used to analyze the self-excitation slip-ring induction generator taking iron loss into account. Also, this paper mainly focuses on the effect of external rotor capacitance (CRotor) on the voltage generated and frequency and compares the results in the absence and presence of these losses. Ignored those losses in slip ring induction generators, especially when connected the external rotor capacitance leads to more effect and large variation in the select proper value of the excitation capacitance. Based on this technique, the obtained 7th-degree polynomial in terms of frequency. The response of (SESRIG) is simulated by matlab/Simulink and the results are compared with experimental results which are obtained from testing machines. The results confirmed the agreement between the practical results and simulation which presented the validity of proposed modelling.