Which comes first?

[Besoeker]

Current can exist without voltage in a superconductor.

Well,, maybe at zero degrees Kelvin. I'm inclined to think that such is not the prevailing condition for the motor in question.........

 

[RumRunner]

Inductor current lags inductor voltage by 90 deg. Current lags voltage by 90 deg in a pure inductive circuit.

Because instantaneous instantaneous power is the product of the instantaneous voltage and the instantaneous current (p=ie) , the power equals zero whenever the instantaneous current current or voltage is zero.
( The above was lifted from All About Circuits textbooks Chap 3)

The following is mine:

The mnemonic instituted by Boston U can be very helpful in remembering the phase difference between current and voltage.

There is a mnemonic “ELI the ICE man”.


With only an inductor in an AC power source there is always a 90deg phase difference between I and E.

To aid in remembering this electronic circuit phenomenon (if you like) involving current and voltage, the “ELI” part which shows the letter line up of the letters in the acronym “E-L-I” signifies that E (voltage ) leads the current in the inductor circuit (L). . .. which in turn signifies that voltage is ahead of the current.

The “ICE” part on the other hand. . . with only a capacitor in an AC power source, there is also a 90 deg phase difference. The voltage lags the current in this case.

This “ICE” part with the capacitor, the voltage (E) is behind the current (I).

I (current) being in the lead.

This is a staple in designing electronic circuits.
Judging from the point of view in regard to “ which comes first” voltage or current . . . I agree with the Brit.

 

[mivey]

I do believe you could present a similar case that starts with a current source and has and in-line capacitor. For that circuit, voltage cannot change instantaneously in the capacitor, so perhaps current comes first.

But not the motor current. In your example the motor current would lag the capacitor voltage which lags the source current.

 

[mivey]

This is like the old adage of what came first, the chicken or the egg. Can one exist without the other?

Either may exist without the other. But to exchange or convert energy, both current and voltage must be present.

In this case, the voltage comes first. We sometimes even model it as applying an ideal voltage source to the motor terminals. Everything else that happens follows the application of the voltage source to the motor terminals.

Current lags the voltage or else the inrush power would be a perfect step function instead of a ramp.

 

[kwired]

I started a new thread where this discussion can continue.

Bad idea? We'll see I guess.

This is like the old adage of what came first, the chicken or the egg. Can one exist without the other?

You can't take that from me, I mentioned that already in the closed thread where this started.

Topic in initial thread was involving an AC induction motor and unexplained high current draw condition FWIW. Then this discussion kind of took over the thread.