The balancing node is generally chosen to be on the busbar of the power plant that serves as the frequency adjustment of the system, why?

The purpose of the balancing node is to ensure the power balance of the system (including active and reactive power), so it is required to adjust the active and reactive power issued at any time according to the needs of the various types of power plants, except for power plants (mostly hydroelectric power plants) that serve as the task of system frequency adjustment, the amount of active power issued by the dispatching center is pre-allocated, and can not be adjusted at will. Therefore, the balance node is generally selected as the bus of the power plant for system frequency adjustment.

Note: The answer to this question depends on the active power, because the balance of reactive power and PV nodes to ensure.