The CURENT Large Scale Testbed (LTB), from CURENT Research Center, is the first of its kind to provide a virtual electric power grid for researchers to experiment with closed-loop controls and algorithms. Research and application ideas can be quickly and seamlessly integrated for verification in this virtual power system. Without CURENT LTB, researchers have to either write a set of additional ad-hoc scripts or manually link multiple tools. Then, they can form a manually operated closed-loop environment or have to run an "open-loop" study without feedback. The CURENT LTB behaves precisely like a virtual power grid with closed-loop capability such that researchers can test their algorithms or controls (as modules or components in the overall CURENT LTB loop) for fast testing and prototyping. Everything is automated with one or a few button-clicks instead of tedious manual operations. The CURENT LTB also integrates power system simulation with communication network emulation to accurately simulate a modern cyber-physical power system with both power flow and information flow. The CURENT LTB is the only open platform available for cyber-physical power system simulation.