Thyristor controlled reactors（TCR） are critical components of static var compensators（SVCs） to ensure the safe and stable operation of SVCs. Comprehensive analysis of fault states of a TCR is given in detail. This includes line to line fault， phase to ground fault and turn to turn fault. TCRs are modeled based on the quasi-steady-state model used in HVDC and extended arbitrarily periodical current to three-phase system. The study shows that the line current of a TCR doesnt contain the third harmonics in the normal condition; however， it does contain positive and negative components of the third harmonics in the fault state. Non-characteristic third harmonic current is introduced and studied qualitatively as well as quantitatively. Numerical simulations using PSCAD validate correctness of the proposed method.