In the past decades, a large number of power electronic converter-based energy resources have been connected to grids around the world. The increasing number of such devices is pushing for both electromechanical and electromagnetic dynamic simulations to be part of routine stability studies for transmission planning studies. Hybrid wave-phasor simulations have been proposed in the literature to address this challenge. This paper describes Open-Instance Wave-Phasor Interface (OpenIWPI), a Modelica library used to couple phasor-based and electromagnetic power system models, allowing simulation and linearization of such hybrid models to be performed altogether. Examples are presented to describe how the library can be useful in power system studies.