Abstract: The 12-phase synchronous generator-rectifierload systems have been widely used in the mobile platform. For the safe operation of the system, this paper analyzed the internal phase-to-phase short circuit fault between different bridge-rectifiers, which is a special type of the stator internal fault in the multiphase system. Considering the special topology of the additional short circuit loop between the two groups of three-phase windings where the fault is located, as well as the variation of the commutation mode of the bridge-rectifier, this paper extended the existing multi-loop mathematical model of 12-phase synchronous generatorrectifier-load system, to calculate electrical quantities including the voltages and currents of stator windings and the rotor windings, and the output voltages of the bridge-rectifiers under the faults. With the experiments on a 12 phase model machine, the accuracy of the simulation results was verified. Based on the simulation and experiment results, this paper analyzed the electrical characteristics of the stator internal phase-to-phase faults between different bridge-rectifiers in the 12-phase machine system. It is especially indicated that the currents of the short circuit loop and some phases in the AC side would decrease as the resistance of the DC load increases. This paper provides the basis for risk assessment and fault protection for the special internal faults in the 12-phase generator-rectifierload systems.