First time here? We are a friendly community of Power Systems Engineers. Check out the FAQ!
Not sure what you are trying to accomplish, however if you want to simulate an equivalent grid representation, you can use the classical generator GENCLS ith high inertia by using a dye record like 99999 'Gencls' 1 999.0 0.0. / Assuming you a generator modeled at bus 99999 in load flow