This paper presents a real-time extension, called SIMSEN-RT, of the simulation software SIMSEN. SIMSEN-RT allows carrying out hardware-in-the-loop (HIL) simulations of power systems using hardware regulators. It can therefore be used to fine-tune regulator parameters or to test the regulator behavior in different operating conditions (emergency shutdown, islanded operation, etc.). SIMSEN-RT runs on a standard PC and needs no expensive hardware. As it is based on an existing simulation tool, hardware regulators can be tested in any power system configuration. SIMSEN RT will be used by Voith Siemens Hydro for HIL tests of turbine governors and voltage controllers.