I agree. It's bloody annoying having so many different types of motor and so many variations in the windings of each. The guy obviously knows what he's talking about as his company makes its revenue from PF correction, but a bit more detail on the precise motor type under discussion would have been handy for sure.
I see you did not actually read the article, or understand it.
They do not.
The reactive components do not vary with load. How could they? Load is by definition in phase current not 'wattless' current.
I know I'm not a power engineer - but I thought it was 240V phase-ground (which is what we all have in our houses) and 415v phase-phase?
AIUI the US uses two phase 220V for power equipment like tumble driers. Each is 110V from earth, and opposite.
Andy
Hmm. I agree that the reactive components within an induction motor do not change dramatically, however the effect of slip ie the difference between rotating field and rotor speed does significantly the effect of how a reactive component is seen supply side.
I really suggest you look at various models of the induction motor and understand them before saying that the reactive component of current is constant.
I have already given one link:
and there are many more websites that give a good overview of induction motors.
If there is anything you don't understand then I would be happy to try and explain it to you here.
To be pedantic, the voltage within the Eurozone is now 230V and 400V respectively.
That is my understanding as well except they are derived from a single phase. Each property or set of properties are supplied with 220v balanced either side of earth, much like a 110v tool isolating transformer that is -55V / +55V either side of earth.
It is of course possible to have any supply voltage if it suits a particular application.
I'm getting a bit long in the tooth and out of date with all the various standards, to be honest. ISTR, though, that back in the 1970s, a lot of
3ph machinery ran off 440V - but that was 40 years ago so it may well be a bit lower today.It completely slipped my mind, but I've got an industrial, 3ph lathe out in the workshop that runs off 240V 3ph. Since I don't have 3ph here I had to buy a single-to-3ph converter to run it. Works like a charm, though! Very civilised having soft starts and infinitely variable speeds with no noticeable loss of torque (which was a big surprise).
There seems some confusion of where the 440 or 400V comes from.
It is the voltage between phases and is 230 x sqrt(3)V. Each phase is still 230V to neutral, assuming there is one!
That link doesn't work, and when IU actually found the the page on that site, it confirmed exactly what I said.
The reactive comnponents do not vary.
I think its you that needs to understand
Do you not accept that the reactive current changes with load?
That's a real shame but there are enough other models out there that take "slip" into account. You do know what "slip" is?
You seem to be deliberately misunderstanding that reactive components do not vary significantly, but we are talking of reactive currents. These are two entirely different quantities, one measured in Henrys and the other in Amps.
An example of what I assume are real motor characteristics
You can do your own sums, but if you calculate reactive current at 50%,
75% and 100% loads they will be around 127A, 136A and 150A respectively.Another example:
I can assure you reactive current does change over motor load.
Well that is not exactly what I said.. Power factor does, because that's a ratio of reactive to resistive.
No analysis, including the one you incorrectly linked to, that I have found on the net has reactive elements varying with slip.
Of course reactive current may vary, but not the value of the inductive elements.
Which means that you don't need to vary the capacitor values with load to get a 50Hz tuned circuit, which was the point.
We seem to finally agree that reactive current does vary with load, then one must infer the inductive element as seem by the supply must vary in sympathy even if the inductive components themselves do not vary significantly. Hence my earlier question surrounding your knowledge of "slip" and models of induction motor.
?? You just agreed that reactive current can vary. That statement just doesn't make sense.
I agree that a fixed capacitor will have a specified lead current but perhaps this is the root of your misunderstanding in your belief that a fixed single sized capacitor will ensure a pf of unity over a motor's load characteristic from stall to no load?
Look, I spent 20 bloody years of my life designing circuits with L C and R components in them. Without active components any generalised collection of LCR has a resonant frequency that does not change on account of the variation in the R. Lord knows it took the invention of valves and transistors to create the wah-wah pedal from a variable resistor, and that works by 'amplifying' a capacitor value.
You have baffled yourself with bullshit.
Its pretty much implied - since changing load will change the slip.
THE LOAD IS NOT A REACTIVE ELEMENT
shheesh
I don't recall anyone saying the load is a reactive component.
Most models have a reactive element in series with the load, which is dependant on slip.
There is also a parallel reactive component, yes. But we're talking of a series component as per X2 in the above link's diagrams.
If you have an inductor and resistor in series, can you accept the reactive current will vary with value of resistor? ______ _____
------|__L___|-----|__R__|------
If you have been working in this field for as long as you have, there is a fighting chance you might accept this hypothesis.
If you claim you can't see this webpage there are many others:
These all have a common theme. A load resistor representing the resistance of the rotor, and an series inductor plus other components that serve only to confuse you.
If after all these years of designing Rs, Ls and Cs in circuits you should should be able to understand the consequence of the supply current to a nominally fixed inductor and a variable series resistor. Even if you have not seen an induction motor in your life you should be able to see that the reactive part of the supplied current with be highest when R is 0ohms, and tending to zero and R tends towards infinity.
Sheesh, and you claim to have worked in this field. How long ago???
Agreed, and so?
... which makes it 400V at 230V, or 415 at 240V. 440 would require the single phase voltage to be 254, which is the absolute top limit.
Andy
John, please ....
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