Grid-scale energy storage systems have become popular for the growth of hybrid renewable power systems. Due to design flexibility, low manufacturing costs for large scale, indefinite lifetime and recyclable electrolytes Vanadium redox flow batteries (VRFBs) are a promising energy storage technology. In this paper, an electrical equivalent model of VRFB which is present in Distributed Asset Research Testing (DART) facility in Texas is proposed. The VRFB is connected to a 3.6kW resistive load. The effect of flow rate and pump power losses has been considered in modeling the VRFB. A control method for State of Charge (SOC) estimation is also proposed as it plays an important role in over-charge/ discharge of VRFB. The entire work is simulated in Matlab/Simulink environment and the results obtained prove the efficient operation of VRFB.