If you want to simulate the synchronisation of two different systems, you can model and simulate both systems as separate networks. After some seconds you can then connect them with a circuit breaker element (ElmCoup).

In the attached example the connection of two networks is shown. One grid has 3  generators and the second grid two, each with the respective voltage controller. These are coupled in time using a circuit breaker.

At 0sec "Load A" in the left side network is switched off, thus the frequency is staring to increase due to the lack of prime mover. The frequency in the right network is constant. The voltages at both sides of the breaker are different due to different controller settings of the transformers.

At 1sec the circuit breaker "Connector" is closed, so you can see either the electromagnetic short-term transients (EMT study case) of the complete network, or the longer term behaviour (RMS study case) of the system. In both study cases some predefined plots are included, the breaker values (P,Q,I and voltages) are also shown.