Frequency Synchronization

Can any two buses in an AC power system have different frequencies? Is it possible to send real power from low-frequency bus to high-frequency bus region in an AC power system?

Yes, and it happens all the time. However the frequency deviations are very small and within the range of normal operations. One bus may be at 60.01 Hz and the other at 59.96 Hz and the system is still stable. Larger frequency deviations would be unstable however as the synchronous generators lose synchronization and their protection systems take them offline.

However is the frequency difference is much larger, then the two AC sections cannot be directly connected. In this scenario, an asynchronous connection using either a DC tie or variable frequency transformer is needed to connect the two grid sections.