Suppose I measure both current and voltage going to an electric motor. So that I have two continuous streams of three phase data (current and voltage).
I want to use this data to diagnose potential problems with the motor. Some motor faults are supposed to have a small effect on the current pattern of the motor.
The way I understand it do changes in the grid mean small variations in the voltage. Either in the RMS or in the frequency of the measured voltage. If these differences are small over time, the grid quality is good. If the differences are big, the grid quality is poor.
Since I measure both current and voltage my intuition says I should be able to go to a representation which is more or less invariant to these small changes in voltage. I was thinking about the instantaneous electrical power.
I know instantanious electrical power is given by:
P(t) = I(t) * V(t)
So I could multiply the current waveforms with the voltage waveforms and get the instantanious power.
However, what I am not sure of is what the effect is of small variations in voltage due to changes in the grid. For example, how do these changes affect the current and the power? I assume the motor runs the same before and after a small variation in the voltage, is that correct? If I look at the instantaneous power instead of at the current, am I less susceptible to changes in the grid than when I look at just the current? Or do you know of other/better ways to compensate for changes in the grid?