This paper presents an analytical approach of the frequency response for the wound rotor induction machine as a possible method for fault diagnosis. This approach is based on mmf, flux and emf computation for both healthy and faulty machines during any operating condition. The proposed technique is applied to study the effect of opening one phase either on stator or rotor sides. The computed harmonics of both stator and rotor currents are experimentally verified on a test-bed based on a small power wound rotor induction machine.