SimPowerSystems includes both Second-Generation and Third-Generation technologies. You have the option to create and simulate an electrical model using Second- or Third-Generation technology.
Third-Generation technology fully uses the Simscape technology, and the component models are written in the Simscape language. You can directly connect these models with components from the Simscape Foundation libraries and with components from other physical modeling products.
Second-Generation technology is specialized and optimized for modeling electrical power systems. The Second Generation block libraries contain a large number of models that use their own electrical domain. You ultimately connect these blocks to other Simscape elements through Simulink signals.
For more information on the difference between these two technologies, see the SimPowerSystems documentation and Release Notes.