High Amps Question

[nuckythompson]

I have a two source bus (one normal utility supply, and a generator supply). This bus has various motors on it. When I transfer the bus to the generator supply, the motors on the circuit draw higher amps. Seems to run fine on the normal source but motor currents ramp up when the generator is supplying the load. Any ideas why this is? Voltage readings show same bus voltage no matter the source.

Thank you.

 

[ron]

Is this during steady state operation or inrush current during startup?
If the voltage is the same, the steady state currents should be the same.

 

[jim dungar]

Are these motors on VFDs?

 

[Jraef]

Most likely it’s an issue with the power factor of your load being low.

 

[synchro]

Not a lot of detail is provided, but the following might explain the OP's observations:
Generators typically have a significantly higher source impedance than the utility at fundamental and harmonic frequencies. Therefore if there are significant harmonic currents from the loads, the harmonic voltages developed across the source impedance will be higher when on the generator. If there are negative sequence harmonics they will develop an opposing torque in the motors. Therefore to compensate, more current at the fundamental frequency will be needed to provide the torque demand from the mechanical loads.