Which of the following is NOT considered a synchronizing variable?

Synchronization in power systems is a critical factor for maintaining system stability and reliable operation of synchronous machines. Synchronizing variables are parameters that indicate how well two power systems or machines are aligned in operation and are crucial when interconnecting or synchronizing generators to a grid.

The phase angle is a key synchronizing variable, as it reflects the relative position of the waveforms of the voltage and current, indicating whether the machines are in phase or not. The frequency difference is likewise significant; it shows how much the frequencies of the two systems differ, which can greatly affect stability if not properly managed. Voltage magnitude difference is another important variable because a significant voltage difference can lead to issues in the connection, impacting current flow and overall stability.

In contrast, the MW flow differential—referring to the difference in megawatt power delivery between two points—is not inherently a synchronizing variable. While it is critical for understanding system load and generation balance, it does not directly impact the synchronization process itself. Instead, it reflects the operational behavior of the system once synchronization has been achieved. Consequently, this choice stands out as the correct answer to the question.