What is the consider to choose the voltage of a generator?
Give me the reason why you choose 380 V, 400 V, 4,3 kV, 6 kV, etc

Greatly depends on the distance the voltage needs to travel. The higher the voltage, the lower the amperage, and smaller wire.

Voltage is decided by the copper loss in the transmission network(cables or overhead line). If the load is a factory near the generator,380v is OK, but if it located far away or distributed over a larger area higher voltage to be considered.