Generac Gen. blows fuses on gen. its self.when started.blows fuse after about three min. run time,have to replace fuse on gen.What is the problem?

Do you have the model number?

The only reason a fuse should blow is an overload. Pull the panel and check the outlets for a loose wire shorting out, or a pinched wire going to the panel.

Yes,
What model number is the generator.
By 'fuse' are you talking about the resetable circuit breakers on the panel?
Does your generator have an idle switch (which sets the engine to idle when there is no load on it)? If so, you shouldn't be trying to start the unit with that switch in the ON position.
You should not have anything plugged into the unit when trying to start and should allow it to warm up for several minutes before attempting to add load, then gradually add the load.
Does the unit actually produce electricity during the short time it is running?
If not, you may need to excite the field.
Let us know what model, we MAY be able to help...

Bob:
How do you "excite" the field.   Physics...   a).  (excite)... to raise the energy of.   b). to raise (an atom, for example) to a higher energy level.
So I'm curious as to how one would "excite the field".    Field????  the windings of the gen. motor???   I find this interesting.

Darn, lost my post....where did it go??
Anyway, the process of 'exciting' a generator was discussed here before. This proceedure is only used when the generator fails to produce electricity, but is turning. Here is something about it......."DYT400005-30-2006, 02:16 PM
Field Flashing of Portable Generators (exciting the field) 

This tip comes from the Briggs & Stratton Customer Education Department. As an alternative to flashing a rotor winding with a battery applied to the brushes, an electric drill may be used. Follow these steps to flash the generator:

* Plug the electric drill into the generator receptacle.

* If the drill is reversible, move the direction switch to the forward position.

* Start the generator

* While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.

Use caution not to get your hand or other materials caught in the chuck. As soon as the field is excited, the generator will produce power and the drill will turn on.

The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor windings, which is fed back through the trigger, cord and into the generators receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field, which is intensified due to the iron core of the stator laminations. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.

If flashing the field does not make the generator work, you may have additional problems, besides a lack of magnetism in the rotor. Further testing will be needed. Hopefully, this will give a simple way to field flash your generator if needed - Bruce Perrault"

I'm not sure if this works on all generators or only specific types. I've never had this problem with either of my Generac generators, but I've heard of others who have.
I hope this answers your question....

Back in the old days we often had to do this on cars running a generator and relay switch.

sounds like a short to me.

Does sound like a short.............

Sounds like a short in the exciter winding. The fuse protects the generator from putting out to much voltage. Had one in Nam that shorted (no fuse) was putting out 480 volts before it burnt up the generator. Thank goodness we had magnetic breakers imagine replacing 10 acres of lighting and equipment (think messhall and coffee maker).