Why does load shedding still occur in jetliners (e.g., 787) when there is so much power available? I had a few questions about how electrical generator works on an aircraft, the 787 to be specific although I know it is similar for all aircraft.

So the 787 engines have 2 VFSG each which are rated at 250 KW each which is 1000 KW -> 1 MW which is said to power a 2000 population town. Since the power is generated using the rotation of the engine, im assuming it does not always produce 1 MW , only at peak rotations?

What on earth in the plane sucks that much energy, I know the 787 is a more electric aircraft, but still how much power does it really take? If the total power output of the plane is 1.45 MW, I'm assuming the APU Gens are able to provide 0.45 MW in total to the airplane.

If there is so much power available, why does load shedding still occur in aircraft?
Load shedding always occurs during engine start, according to the FCOM of the B789. Both engines are allowed to start simultaneously. The B789 engines are started using both VFSGs of each engine, which are mechanically connected to the N2 shaft via the accessory gearbox. So, the VFSGs are using power instead of delivering during engine start. The APU cannot provide enough power to prevent load shedding.

If the engines are started using external power, at least two 90 kVA external power sources are required. Optimal start performance is achieved using 3 external power sources (2 on the left forward fuselage and 1 behind the left wing on the fuselage). If only 2 external power sources are used, significant load shedding can occur (e.g. First Officers displays blanks and even the audio control panel receive and trasmit selections may be lost).

The APU is normally switched off during flight, unless e.g. one VFSG is U/S.

Load shedding should normally not occur when both engines are running and all VFSGs are operational (I haven’t experienced load shedding during flight).