Deployment of Synchronous Condensers (SynCons) has become one popular solution in accommodating large-scale renewable energy source (RES) for existing power systems. However, as a rotating device, SynCon may lose transient rotor angle stability caused by injected active power from nearby RES after a fault. To reveal this phenomenon, the transient stability of SynCon is investigated in this paper. To derive intuitive mechanism and assist quantitative analysis, the equivalent synchronous generators (ESG) model is proposed to characterize the transient behavior of SynCon and co-located RES. The Lyapunov's direct method is employed for the assessment of transient stability by analyzing attraction domain for a typical benchmark system. On this basis, an index of transient stability margin against grid strength and an adaptive low voltage ride through (LVRT) control strategy are proposed for further assessment and enhancement of transient stability. The accuracy and effectiveness of the proposed methods are verified with EMT simulations of a typical windfarm configuration.