Does Torque Change Along With kw in a Generator?

Power =torque times angular speed. So if power changes, so does torque.

If the generator needs 10 KW, the driver has to supply 10KW plus any power losses in the train.

http://en.wikipedia.org/wiki/Torque

correct

u need 20hp to let it run smoth, the driver should be 1.5 times bigger than the load

R.u

1.5 is pretty conservative for a generator drive... There should not be 50% loss in the system...

A 20 hp engine would not be unusual. For example: http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_398826_398826

Typically a "20 hp" engine is a peak rating. This generator has a 10,000 watt continuous rating. 13,000 watts (the generator peak rating) corresponds to 17.4 hp, so if the figures are accurate, the generator is about 87% efficient.

Torque (and consequently hp actually produced) change with load. If your generator is under light load, the engine will produce only a few hp.