The objective of the proposed research is the modeling and simulation of power system with high penetration of inverter-based resources with a focus on cold start capability and protection of the system. Grid-forming (GFM) inverter, as the critical device in IBR-dominated system, is modelled in quasi-dynamic domain using WinIGS and in time domain using PSCAD. A test system with up to 100% IBR penetration is also modeled to evaluate the performance of the GFM inverter. The Estimation-based Protection (EBP) method is implemented in a real-world PV-integrated distribution system, proving its effectiveness in detecting faults within non-radial distribution systems with bidirectional current flow as well as low fault current level. A high-fidelity model of Battery Energy Storage System (BESS) with battery degradation and Battery Manage System considered is also proposed. With the high-fidelity model of GFM inverter and BESS, the dynamics and performance of power systems with high IBR penetration can be simulated more accurately.