A self excited generator fails to excite if driven at too low speed because at too low speed no voltage will be induced in the armature winding, there will be no field current in the field winding and consequently it will fail to excite.
A self excited generator fails to excite if driven at too low speed because at too low speed no voltage will be induced in the armature winding, there will be no field current in the field winding and consequently it will fail to excite.