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Old 15th Jan 2019, 11:19 pm   #81
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Default Re: Switched or Unswitched Sockets for HI-FI?

Now it's 394 amps.
Could someone please give an exact figure as to how many amps caused the cable to blow up?
I need a lie down after the traumatic physics lesson.
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Old 15th Jan 2019, 11:23 pm   #82
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Default Re: Switched or Unswitched Sockets for HI-FI?

It's still the best part of 700 amps, whichever way you slice it and dice it, shoving nearly fifty times the usual amount of power through the resistance of the cable. I think the appropriate word is "ouch". And if the cable is already in direct sunlight, that's not going to help any either. More like "Whoomph" maybe? I know I wouldn't want to be in that meeting room, the moment the laughter stopped .....

Strong sunlight can have all manner of unexpected effects, though. I've heard tales of buildings with windows angled such that they focused the sun's rays onto a point .....

This is why it's always a good idea to get someone else to have a quick look at your plans who isn't involved with your project. They might see something to which you have inadvertently developed a blind spot.

As for the pole, if the fire was extinguished quickly and not left to smoulder, it is unlikely to have weakened it much -- or else it would already have toppled anyway. The unburned heavy resins and tars will resolidify, reinforcing the charcoal matrix like a poor person's carbon fibre.

EDIT: OK, not 700A through a 100A rated cable because it's 3-phase. But however you slice it and dice it, that power is being evenly shared among the three conductors. Each of the three phases is carrying one third of the total current. At 11kV, that's 3.3MVA. So it's being overloaded with just 2.273 times the rated power.
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Old 15th Jan 2019, 11:44 pm   #83
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Default Re: Switched or Unswitched Sockets for HI-FI?

I take it that means it's close to 300 amps then?
Either way, I'm gonna have a nervous breakdown any time soon.
To keep it simple and cover everything, it's now 1000 amps instead.
Rick.
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Old 15th Jan 2019, 11:45 pm   #84
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Default Re: Switched or Unswitched Sockets for HI-FI?

The real damage to the pole was probably not from the simple ohmic heating, but probably from the arc after a conductor had parted.

Remember that this was done by nice friendly, cuddly, electrons from a solar farm! Not nasty aggressive nuclear ones.

All that poor cable had to run before would have been an oat-bruiser for the stallions.

David
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Old 15th Jan 2019, 11:45 pm   #85
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Default Re: Switched or Unswitched Sockets for HI-FI?

That is right. There are indeed three phases.
The amplifier would have to have electrostatic speakers running from the raw DC with high voltage FET output stages.
Output power would vary according to light levels unless you had a very long string of SLA batteries to keep the amps and stage light show going into the night.
At least it would be running on "fresh" electrons that have never alternated on there journeys to the amplifier and no transformers for them to get wound up in.
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Old 15th Jan 2019, 11:46 pm   #86
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Default Re: Switched or Unswitched Sockets for HI-FI?

Quote:
Could someone please give an exact figure as to how many amps caused the cable to blow up?
394A

There are three lines with 11kV between them. Consider the load as three loads of one third the power, connected in delta.

Vphase (voltage across each load) = Vline (voltage between the lines)
Iphase (current through each load) = Iline / sqrt(3)

Thus,
I = Ptotal / Vline * sqrt(3) / 3
= 7.5MW / 11kV / sqrt(3)
=394A

Why Sqrt(3)?
The line current is the vector sum of the two connected phase currents, which differ in phase by 120°.
Thus, Iline = 2 * cos(30) = 1.732
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Old 15th Jan 2019, 11:50 pm   #87
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Default Re: Switched or Unswitched Sockets for HI-FI?

Quote:
Originally Posted by julie_m View Post
Strong sunlight can have all manner of unexpected effects, though. I've heard tales of buildings with windows angled such that they focused the sun's rays onto a point .....
Was that not the mobile phone building in London that roasted a road and toasted parked cars to form a tar based automotive pizza
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Old 16th Jan 2019, 12:02 am   #88
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Default Re: Switched or Unswitched Sockets for HI-FI?

The Walkie Talkie.
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Old 16th Jan 2019, 12:20 am   #89
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Default Re: Switched or Unswitched Sockets for HI-FI?

You are right it was the walkie talkie.
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Old 16th Jan 2019, 12:22 am   #90
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Default Re: Switched or Unswitched Sockets for HI-FI?

Lucien, thanks for clearing that one up, although square roots mean nothing to me.
Let me explain the situation as to why my maths skills are almost non existent, I have a mental condition which affects my ability to learn certain things, I can learn most things but maths is one thing that never registers in a hurry, it would take me at least 20 years or more to be on your level with maths, hence why I have to have things in laymans terms.
Rick.
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Old 16th Jan 2019, 12:41 am   #91
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Default Re: Switched or Unswitched Sockets for HI-FI?

The square root of a number is another number which when multiplied by itself gives the first number- egg: 5 is square root of 25, 10 is square root of 100 etc etc.

Looking at the line current question another way, add an imaginary neutral ( you can 'cos the system is balanced so there is no neutral current to need an actual wire). The l-n voltage of a 3-phase system is l-l voltage / sqrt3 so for 11kV l-l you get 6.351kV l-n. Total power is now simply l-n volts times l amps times 3.

So line current is 7,500,000 / 6351 / 3 = 394A as already quoted.

Near enough a four fold overcurrent for 100A rated cable. Or sixteen times the cable dissipation- in fact somewhat more as the cable resistance increases with increased current loading.
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Old 16th Jan 2019, 1:22 am   #92
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Default Re: Switched or Unswitched Sockets for HI-FI?

5 x 5 = 25, that's simple enough, now it's starting to make sense, I'll go over all the other figures when I'm more awake.
One has to go to sleep.
Rick.
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Old 16th Jan 2019, 3:27 am   #93
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Default Re: Switched or Unswitched Sockets for HI-FI?

Wiring for the very best sound reproduction should be done entirely in either the old colours OR the new colours, do not tolerate a mixture of the two.

Mixed colours confuse and stress the electrons, this makes them tired and less able to respond promptly.
Higher frequencies will therefore lack clarity.

Also, if your house is wired in the old colours, then fit a red and black mains lead, so as to minimise colour stress to the electrons as they pass from the fixed cables and into the appliance flex.

Conversely if your house is wired in the new colours, do not tolerate any old flexes on audio equipment, change them to blue and brown.

Some stress may be unavoidable if the mains in the street use different colours.
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Old 16th Jan 2019, 12:35 pm   #94
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Default Re: Switched or Unswitched Sockets for HI-FI?

I've been toying with the idea of getting a three phase supply installed so I can choose which one to use for best fidelity. I suspect the best one will change from time to time depending on what my neighbours are doing.

If I go ahead it would open up the possibility of a three phase amplifier. Has anyone seen a suitable design?
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Old 16th Jan 2019, 1:35 pm   #95
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Default Re: Switched or Unswitched Sockets for HI-FI?

If you think your neighbours are superimposing noise on your mains then it would probably be cheaper to get a filter to block it.

EDIT: Or a hi-fi system whose power supplies are adequately filtered internally.

Cheers,

GJ
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Old 16th Jan 2019, 2:48 pm   #96
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Default Re: Switched or Unswitched Sockets for HI-FI?

They do make 6 speaker amplifiers so you get two speakers per phase.
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Old 16th Jan 2019, 5:27 pm   #97
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Arrow Re: Switched or Unswitched Sockets for HI-FI?

I based my calculations on the data stated in post #68 by Refugee, q.v. There was no mention of 3-phase therein.

Al.
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Old 16th Jan 2019, 5:29 pm   #98
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Default Re: Switched or Unswitched Sockets for HI-FI?

If you had 3-phase supply, you could have separate amplifiers for Left and Right, and a centre Baxandall bass.
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Old 16th Jan 2019, 6:33 pm   #99
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Default Re: Switched or Unswitched Sockets for HI-FI?

Does that mean that with three phase and six speakers the apparent source of hum would come from a point appearing to rotate in a circle?

Swapping two phases would reverse rotation.

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Old 16th Jan 2019, 11:48 pm   #100
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Default Re: Switched or Unswitched Sockets for HI-FI?

The smoothing capacitors would not need to be quite as large as they would for single phase.
The ripple would be 300hz.
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