Authors present a power flow tracing based method for usage and loss allocation along with FACTS devices. Graph theory is the basis for usage allocation. Modified Kirchhoff matrix is used for this purpose. FACTS devices are used in the system for various purposes such as reactive power compensation; voltage profile improvement etc. hence in this paper Thyristor controlled series controller (TCSC) with voltage source modeling is used for finding the effect of FACTS device on transmission usage and loss allocation. A sample 5 bus is used for this purpose.