​$$\text{The voltage equation of a DC long-shunt compound generator is } \\\text{(where } E_g \text{ is generated EMF, } V_t \text{ is terminal voltage, } I_a \text{ is armature current, } R_a \text{ is armature resistance, } I_L \text{ is load current, } R_{se} \text{ is series resistance, and } V_{\text{brush}} \text{ is brush contact drop)}$$​​