Currently many power-electronic-based devices are being connected to the electric power grid. An efficient way to study the interaction between these devices' controllers, and the resulting electromagnetic and electromechanical responses is to use hybrid wave-phasor simulations. Many solutions involving the co-simulation of electromagnetic (EMT) and transient stability (TS) models have been proposed in literature, with different techniques being employed for the calculation of a phasor from the wave quantities. This paper presents a Modelica implementation of a hybrid interface that enables the coupling of two portions of a power grid, with each portion defined in models in two different time-scales. The interface is used in Modelica-compliant environment to interface a STATCOM, as an EMT model, with a single machine infinite bus system, as the phasor model. Results to assess the interface performance and the STATCOM implementation are presented.