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Real Load Division
Division of real load among paralleled generators becomes necessary, because it is not possible to attain exactly identical speed governor settings on all four generator constant speed drives.
Therefore, in a paralleled system, the generator which has the highest speed governor setting will carry more than its share of real load. The unbalance in real load among paralleled generators is
detected by means of current transformers and a real load division loop, whereby signals proportional to the unbalance are supplied to control devices which correct the torque on the generator rotors.
The frequency of an isolated generator is determined by the initial setting of the basic speed governor on its associated constant speed drive. Since the a.c. generators are synchronous machines, two or more generators operating in parallel will be locked together with respect to frequency, whereby the frequency of the paralleled system is that of the generator which supplies the highest frequency. If the speed governor setting on one constant speed drive is higher than others in a parallel operating system, its associated generator will motor the generators with which it is paralleled. In this case the generator with the higher speed governor setting rotates at the same speed as its constant speed drive output, but since each generator is mechanically coupled to its constant speed drive through an overrunning clutch, the generators which are being motored rotate at a speed which is higher than their associated constant speed drive output speeds. Therefore there is less transfer of energy from the constant speed drives to the generators which are being motored. Since the energy supplied to the motored generators originates from a generator with a higher speed governor setting, this generator carries more than its share of real load and the motored generators carry less than their share of real load. To equally divide real load among parallel generators, equal amounts of energy must be supplied in the form of torque on the generator rotors.