Under loaded electro motor power consumption

Just a basic analysis if your motor is rated for 30 kW then the rated HP is 40 and actual load on the motor will be 29.5 HP. If the source system is considered stiff then supply frequency doesn't change. Torque varies with the motor terminal voltage squared so the torque being at 75% of motor rating means voltage can be decreased to 87% to have run adequately (assuming slip stays constant).

Reality is that the supply voltage (again system is stiff) will not drop so to compensate slip must drop by 25%. So if the slip is at 5% then the motor being loaded at 75% means the slip drops to 1.25% which ultimately means rotor speed increases near synchronous speed.

So what does that mean to the system in terms of voltage, current, and power factor? Voltage will remain relatively unaffected if the system is stiff or tightly coupled, load current of the motor will drop but overall current will increase because requirement for core magnetization and leakage flux of both the stator and rotor and lack of "resistance" due to mechanical load to restrict current flow. This will result in a slightly lower power factor.

This is all theoretical and factual values can be proven with field trial test. If the motor has no load connected to it the rotor circuit is just purely a short circuit and the current flowing will be traveling over the leakage reactances hence VAr consumption increases and reducing current.

Overall current would increase because less mechanical load to act as a "resistance" to limit current flow. So current goes up but that increased has to flow through the leakage reactance of both stator and rotor therefore increasing VAr consumption reducing both voltage and power factor.

Ugh finally in front of a computer. But for real practicality purposes that this isn't an issue for the jet engine but your power factor will suffer slightly and current may increase slightly as well as the windage losses.

To understand this look up the classical induction motor electrical representation, observe the equations, look up the Torque/speed curve, and play with the variables varying them to see what happens as one variable changes as others are held constant.

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