Question about Mvars flow in the power networks. bashier

my question related to the power flow in the network of power, although we know the power is the sum of active and reactive power, the two components of power are not related to each other in the flow of power in high voltage lines and the flow depend on the need of load for active or reactive, we know also the active power are the sum of load power and losses in the equipment and lines, my question is that the reactive power is absorbed or generated from compensation or generator has big affect on the voltage what we shall do to balance the generated and absorbed Mvar in the network, I think it is big big problem for the weak networks, and the engineers in the planning must look to the wire design for long high votage transmission line, and keep in mind what they do in the behaviour of load during the day for peak load, medium , or light one