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If the power factor of 500 KVA, 21 KW, 3-phase star connected alternator is increased from its initial value, then the efficiency of the synchronous generator will _______.
become zero
decrease
remain constant
increase
increase
The efficiency of a synchronous generator is defined as the ratio of output power to input power. As the power factor increases for a constant load in KW, the armature current IaтАЛ decreases to maintain the same real power, which subsequently reduces the Ia2тАЛRaтАЛ copper losses, thereby increasing the overall efficiency.
IS 4889:1968
The efficiency of a synchronous generator is defined as the ratio of output power to input power. As the power factor increases for a constant load in KW, the armature current IaтАЛ decreases to maintain the same real power, which subsequently reduces the Ia2тАЛRaтАЛ copper losses, thereby increasing the overall efficiency.
╬╖=PoutтАЛ+PlossesтАЛPoutтАЛтАЛ тАФ Efficiency formula for the alternator
PcopperтАЛ=3Ia2тАЛRaтАЛ тАФ Stator copper loss calculation
ILтАЛ=3тАЛVLтАЛcos╧ХPтАЛ тАФ Relationship between current and power factor
The electrical power output is given by P=3тАЛVLтАЛILтАЛcos╧Х. For a constant real power P and constant terminal voltage VLтАЛ, the line current ILтАЛ is inversely proportional to the power factor cos╧Х. Since the copper losses in the stator windings are directly proportional to the square of the armature current (Ia2тАЛRaтАЛ), an increase in power factor results in a significant reduction of these losses, improving efficiency.
For a fixed real power output in KW, increasing the power factor reduces the current drawn from the alternator.
Copper losses (I2R) constitute a major portion of machine losses, hence their reduction directly enhances efficiency.
The KVA rating of the machine is the apparent power limit, which remains independent of the load power factor for the purpose of this efficiency relationship.
Reduced thermal stress on stator windings
Improved voltage regulation of the alternator
Requires external reactive power compensation (like capacitor banks) to achieve high power factor
Does not improve mechanical windage or friction losses
Power system stabilization
Industrial power distribution optimization
Option B (decrease) is incorrect because higher current would imply higher losses.
Option C (remain constant) is incorrect because efficiency is load-dependent and loss-dependent.
D is correct тАФ The efficiency increases because higher power factor reduces armature current, leading to lower copper losses for a constant real power output.
Always remember: For a constant real power load, the current I is inversely proportional to cos╧Х. If the power factor improves, the current drops, significantly reducing resistive power losses (I2R).
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