One of those annoying electrical questions


[62 lines snipped]

John, please ....
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On 02/01/2016 10:31, The Natural Philosopher wrote:

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 http://electronics.stackexchange.com/questions/149296/is-power-consumed-by-a-motor-under-various-load-conditions-constant
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: http://emadrlc.blogspot.co.uk/2013/01/chapter-5-starting-of-induction-motors.html At one extreme the reactive current at stall is 4.8 x full load current. At full load the reactive current would be 0.6 x full load current. That is a range of 8:1 in reactive current.
I can assure you reactive current does change over motor load.
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On Wednesday, 30 December 2015 23:58:42 UTC, Cursitor Doom wrote:

You're not going to get resonance when it's connected to the mains, which has close to zero impedance. Aim for 1.
NT
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On Thu, 31 Dec 2015 06:38:49 -0800, tabbypurr wrote:

***Watch out, guys! Troll alert!!!
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On Thursday, 31 December 2015 21:15:19 UTC, Julian Barnes wrote:

If you have some actual content with some relevance, feel free to provide it. Otherwise you are merely trolling.
NT
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On Thu, 31 Dec 2015 13:51:44 -0800, tabbypurr wrote:

I doubt anyone with any sense would waste their time with you. You have already demonstrated that:
A) electronics is not your field (to put it politely)
B) when things are patiently explained to you at great length by several well-meaning people you persist in clinging to your erroneous notions of how things work.
If you're not a troll you certainly have a sub-standard IQ.
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On 30/12/15 23:42, Fredxxx wrote:

the E6 range is 1, 1.5, 2.2, 3.3, 4.7, 6.8 ....
So either a 47uF or a 68uF would be likely choices.
56 is part of the E12 series and 62 would be E24
It's possible you could get a high voltage tight tolerance AC capacitor, but mostly in this game its all about 'near enough'
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On 22:48 30 Dec 2015, Cursitor Doom wrote:

Well done Fred!
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On Wednesday, 30 December 2015 17:41:04 UTC, Cursitor Doom wrote:

440V single phase? How is that?
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What else would you call it?
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On 31/12/2015 08:23, harry wrote:

OMG
I suggest you look up single phase supply.
The OP also missed out that we are working at 50Hz, though less surprised you didn't spot that.
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On Thu, 31 Dec 2015 12:43:07 +0000, Fredxxx wrote:

Eh?? I stated 50Hz in the original question - you wouldn't have got the right answer otherwise!
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On 31/12/2015 12:49, Cursitor Doom wrote:

Oooh - you did. It's normally a given!
Apologies.
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On Thu, 31 Dec 2015 00:23:22 -0800, harry wrote:

You seem to have an association in your mind between 440V and 3-phase since all the 440Vs you've ever seen have probably been 3-phase. But that doesn't mean that you can't have 440V single phase. You can also have 230V 3-phase, too, which I believe is the standard in the US.
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On 01/01/2016 13:48, Cursitor Doom wrote:

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
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On 01/01/2016 20:14, Vir Campestris wrote:

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.
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On Fri, 01 Jan 2016 20:14:27 +0000, Vir Campestris wrote:

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).

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On 01/01/2016 22:30, Cursitor Doom wrote:

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!
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On 01/01/2016 22:55, Fredxxx wrote:

<snip>

... 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
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