On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch Grid to
the German one to the Swiss one etc etc. It doesn't in the main involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

If they are, then they have relatively long borders which means lots of
interconnections.

You aren't going to hold 2 disparate grids in sync with one or two cross
channel links - National Grid has enough trouble holding the UK grid in
phase between Scotland and the South (they have (or had at Bankside at
least) a phase indicator colloquially known as the "scottish wobblemeter".

If it started oscillating, a certain amount of panic ensued...

There is potentially 'as big a problem' with the UK grid system if it splits
during a major disturbance into a two or more islands of load and generation. In
this case (since the late 80's or so) the synchronising systems have an
additional mode where they just sit there primed until the phase angle and
voltage discrepancy falls with certain limits (which are deliberately set wider
than for normal operation) and the breaker then closes, a successful closure
could potentially take a few hours.

Yes. There's an interesting document that you can google for which
outlines the Nat Grid Blackstart procedure. Rather involved...

As the grid system operator is separate from the generation operator in the UK
there is no generation intervention required as such, just switchgear that can
take occasionally take a bit of abuse and generator governors that can hold a
set point frequency.

P.S. There is a long established 400kV AC link between Spain and Morocco with a
similar distance underwater to the UK - French link.

Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

jgh

On 28/07/2014 10:01, Tim Watts wrote:
On 28/07/14 08:27, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 08:13, Tim Watts wrote:
On 28/07/14 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


How many would then die from fires caused by wiring problems?

The biggest cause of electrical fires is overloading of circuits. As we
are not upgrading any existing system, but are starting from scratch and
designing everything anew, with the benefit of present knowledge, we
could build everything to accept heavier overloads and to have much
greater and localised integral overload protection. The result could
well be a reduction in deaths from electrical fires.


And these for sockets:

https://www.google.co.uk/shopping/pr...14369083997541

Exactly the type I used for the computer stack at my factory. I still
have much of a reel of 16mm flex that I used for the plug. I keep
meaning to use some of it to replace the bit of 10mm cable that connects
to the back of my cooker.

--
Colin Bignell

On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

It doesn't. BUT it has a higher out of phase current flowing through it
due to greater capacitance to earth.



jgh



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 13:29, John Williamson wrote:
On 28/07/2014 08:23, harryagain wrote:
"The Natural Philosopher" wrote in message
...
On 27/07/14 23:49, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and
the UK? So DC is a natural choice if you have to re-invert it. And if
you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a
secondary reason to a fairly immutable primary problem.

No. I visited the first link to france at the UK end and the issue is
primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that
suffers resistive losses.

Big ones


Drivel
Capacitance does not cause any losses.
It does cause phase shift and instability.
When the cable is under load it will actually help with phase shift.
Only resistance causes losses.

Whenever current is passing through any imperfect conductor.

On an AC transmission line, current is constantly being drawn to alter
the voltage across the line capacitance to earth. So the capacitance is
the cause of the resistive losses.

Loading a cable has no effect on the phase shift you mention, unless
that load is reactive, and depending on whether it is inductive or
capacitive, it can then either worsen or improve the situation.

Where exactly is this arc drawn for 30 minutes and for what purpose.?


The arc *can* be drawn by using the DC charge stored in the cable. No
claim was made that it ever had been drawn either deliberately or
otherwise, though it's the kind of trick that installation engineers
have been known to pull as a joke, or that happens when things go wrong
when commissioning plant of this sort.

No, They said that once they had switched off each end, that was what
they did to discharge the cable


The greens are planning to use this effect to store energy in their
proposed long distance links for their beloved European renewables
Supergrid, all of which *you* have mentioned here in the past.

Should we add memory loss to your minimal comprehension skills?



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 13:31, newshound wrote:
On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
On 27/07/14 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables
too.
Dielectric losses in air are low.

No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

You are quite right, of course. But the term "dielectric loss" is the
one which CEGB trainers used to use when lecturing mixed classes of
mathematicians, physicists, and all types of engineer to explain why
pylons were the prefered method of transmission, with underground cables
the least desirable from the viewpoint of efficiency.

It's a convenient if not very precise shorthand.


Its not. It is plain WRONG because 'dielectric' losses are losses
incurred IN a dielectric due to it having e.g. resistance.

http://en.wikipedia.org/wiki/Dielectric_loss


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 13:35, John Williamson wrote:
On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

There is a niggling, and mostly insignificant loss in that the
insulation isn't a *perfect* dielectric, but yes, the main losses are in
the conductors.



That I can agree with..


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

Most of Europe is phase locked.

There is an interesting situation also in that Germany's neighbours are
actually being forced to balance the N-S parts of Germany's grid because
Germany itself has loads of solar power in the south and wind power in
the north and there are significant power flows between N and S in
excess of what the German grid alone can handle.

The cost of handling the excess is borne by e.g. Czech republic which
has made serious noises about disconnecting itself from Germany as the
whole power flow is destabilising its own grid.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?


It doesn't. It has a lower Line-Earth reactance (capacitative) - at
least that is what's being claimed.

However, the cables are all armoured so it does not really matter if
they are in a dry tunnel or under the sea.

The big difference is a cable vs overhead lines.

On 28/07/14 15:19, The Natural Philosopher wrote:
On 28/07/14 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

Most of Europe is phase locked.

Fascinating. I would have thought they would have avoided that due to
the buggeration factor.

Is there a supergrid organisation that manages this euro-grid at the top
level then?

On 28/07/2014 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

All the mainland European networks are phase locked by necessity, as
they move power from one to the other on a regular basis in all directions.

If they are, then they have relatively long borders which means lots of
interconnections.

They do.

--
Tciao for Now!

John.

On 28/07/2014 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

The *resistance* doesn't change. When transmitting AC, however, the
*impedance* does change, both due to the capacitance to earth, and, if
the frequency is high enough, "skin effect", which is where the current
flow is restricted to the areas near the surface of the strands also
starts to come into play.


--
Tciao for Now!

John.

On 28/07/2014 10:18, Brian Gaff wrote:
Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!


You could say that. Or you could just call it huge.



--
Tciao for Now!

John.

wrote in message
...
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

jgh

All AC circuits have resistance, inductance and capacitance.
With long cables, the resisatance and capacitance effects become more
important.

Capacitance depends on the nature of the insulation, the surface area of the
conductors and the distance apart they are.
With overhead cable, the distance apart is much greater than with
underground cables.
So capacitance is much more with the latter.
Also the permitivity of air is much less than plastic insulation.

"John Williamson" wrote in message
...
On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

There is a niggling, and mostly insignificant loss in that the insulation
isn't a *perfect* dielectric, but yes, the main losses are in the
conductors.


There is a small amount of energy taken to reverse the electric field.
https://en.wikipedia.org/wiki/Dielectric_loss

On 28/07/14 16:06, Tim Watts wrote:
On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?


It doesn't. It has a lower Line-Earth reactance (capacitative) - at
least that is what's being claimed.

However, the cables are all armoured so it does not really matter if
they are in a dry tunnel or under the sea.

Mmm. Not sure that is so, but cant put a finger on why I feel its
different..


The big difference is a cable vs overhead lines.


Yes.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 16:09, Tim Watts wrote:
On 28/07/14 15:19, The Natural Philosopher wrote:
On 28/07/14 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

Most of Europe is phase locked.

Fascinating. I would have thought they would have avoided that due to
the buggeration factor.

Is there a supergrid organisation that manages this euro-grid at the top
level then?

I really don't know.

I think each nation has its own but presumably they have to phase lock
with each other before they start interconnecting


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Mon, 28 Jul 2014 10:39:58 +0100, "Robin" wrote:

That is the number of deaths and serious injuries in the UK every
year. Around 2.5 million people in the UK also receive a mains voltage
electric shock every year.

Figures from an Electrical Safety Council surveys which have long left
me a bit puzzled. As regards the 2.5m electric shocks, family etc I've
asked (who include people in work and retired, people with young
children, people in rented accommodation etc) don't seem to get shocks
at that rate. So I wonder who/where they are. And as regards "serious
in jury", they define that to include "severe pain" (and all whether or
not medical treatment required).

In the TV repair trade, getting a painful belt was almost a daily
occurrence and elicited little comment, other than ones swear word of
choice. I'm perplexed how the ESC managed to catalouge what was never
reported.




--

Graham.

%Profound_observation%

On 28/07/14 17:11, John Williamson wrote:
On 28/07/2014 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

The *resistance* doesn't change. When transmitting AC, however, the
*impedance* does change, both due to the capacitance to earth,


so far so good


and, if
the frequency is high enough, "skin effect", which is where the current
flow is restricted to the areas near the surface of the strands also
starts to come into play.


Yep a couple of hundred megahertz is what we transmit power at these days!



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

"The Natural Philosopher" wrote in message
...
On 28/07/14 08:22, John Williamson wrote:
On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.


So, having taught grandmother to suck eggs, where is the power loss due to
inductance?

The loss arises from energy taken to reverse the magnetic field.
https://en.wikipedia.org/wiki/Magnetic_hysteresis

On 28/07/2014 19:18, The Natural Philosopher wrote:
On 28/07/14 17:11, John Williamson wrote:
On 28/07/2014 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables
too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?

The *resistance* doesn't change. When transmitting AC, however, the
*impedance* does change, both due to the capacitance to earth,


so far so good


and, if
the frequency is high enough, "skin effect", which is where the current
flow is restricted to the areas near the surface of the strands also
starts to come into play.


Yep a couple of hundred megahertz is what we transmit power at these days!

It can seriously affect stuff as low as 455kHz, if you remember the Litz
wire we had to use for IF transformers in AM radios back in the day.

The thicker the conductor, the stronger the effect, and it is even
noticeable at 20kHZ, according to this site:-

http://www.belden.com/blog/broadcast...-Frequency.cfm

Not noticeable in the special case we're discussing here, but I did say
"if the frequency is high enough" in the general case.
--
Tciao for Now!

John.

On 28/07/2014 19:08, harryagain wrote:
"John Williamson" wrote in message
...
On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

There is a niggling, and mostly insignificant loss in that the insulation
isn't a *perfect* dielectric, but yes, the main losses are in the
conductors.


There is a small amount of energy taken to reverse the electric field.
https://en.wikipedia.org/wiki/Dielectric_loss


I just said that.

--
Tciao for Now!

John.

On 28/07/2014 19:20, harryagain wrote:
"The Natural Philosopher" wrote in message
...
On 28/07/14 08:22, John Williamson wrote:
On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.


So, having taught grandmother to suck eggs, where is the power loss due to
inductance?

The loss arises from energy taken to reverse the magnetic field.
https://en.wikipedia.org/wiki/Magnetic_hysteresis


Not in copper or aluminium wires.

--
Tciao for Now!

John.

In article , The Natural Philosopher
scribeth thus
On 28/07/14 16:06, Tim Watts wrote:
On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?


It doesn't. It has a lower Line-Earth reactance (capacitative) - at
least that is what's being claimed.

However, the cables are all armoured so it does not really matter if
they are in a dry tunnel or under the sea.

Mmm. Not sure that is so, but cant put a finger on why I feel its
different..


The big difference is a cable vs overhead lines.


Yes.



Yep water -v- air cooled...

--
Tony Sayer

On 28/07/14 19:16, The Natural Philosopher wrote:
On 28/07/14 16:06, Tim Watts wrote:
On 28/07/14 14:48, wrote:
Nightjar wrote:
It's losses in the dielectric, so it applies to underground cables
too.
Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, (...)

Sorry, I still don't understand this. We're talking cables not
capacitors.
How does a 16mm2 PVC insulated cable have a higher resistance if it's
immersed in water than if it's in a vacuum?


It doesn't. It has a lower Line-Earth reactance (capacitative) - at
least that is what's being claimed.

However, the cables are all armoured so it does not really matter if
they are in a dry tunnel or under the sea.

Mmm. Not sure that is so, but cant put a finger on why I feel its
different..

A normal armoured cable would have a pretty effective faraday screen
around the live cores.

Not sure about mega HV cables but I'd be surprised if they were not
fully screened too.


The big difference is a cable vs overhead lines.


Yes.

On 28/07/14 19:17, The Natural Philosopher wrote:
On 28/07/14 16:09, Tim Watts wrote:
On 28/07/14 15:19, The Natural Philosopher wrote:
On 28/07/14 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

Most of Europe is phase locked.

Fascinating. I would have thought they would have avoided that due to
the buggeration factor.

Is there a supergrid organisation that manages this euro-grid at the top
level then?

I really don't know.

I think each nation has its own but presumably they have to phase lock
with each other before they start interconnecting



So I wonder who regulated the frequency?

And what happens if one end starts to "wobble" (phase angle
oscillation)? Do they just island the country.

On 28/07/2014 10:09, Tim Watts wrote:

I would say we might as well have 400V as 230V and more or less halve
the conductor sizes. Much more than that is getting silly though.

I'd vote for the standard domestic supply being 3x32 A (3-ph) instead of
1x100 A. Then we'd have the advantages of 3-phase for motors and
rectification, and could have 400 V appliances like cookers and showers
hooked-up with 2.5 or 4 mm^2 cables. Proposals now required for a
compact 5-pin 16 A plug & socket...

--
Andy

On Mon, 28 Jul 2014 19:17:33 +0100, The Natural Philosopher
wrote:

On 28/07/14 16:09, Tim Watts wrote:
On 28/07/14 15:19, The Natural Philosopher wrote:
On 28/07/14 14:20, Tim Watts wrote:
On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch
Grid to
the German one to the Swiss one etc etc. It doesn't in the main
involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

Most of Europe is phase locked.

Fascinating. I would have thought they would have avoided that due to
the buggeration factor.

Is there a supergrid organisation that manages this euro-grid at the top
level then?

I really don't know.

I think each nation has its own but presumably they have to phase lock
with each other before they start interconnecting

Germany Austria and Switzerland also operate another interconnected
network at 16.7Hz which is what most of their electrified railways
use. The lower frequency suited the simple motors and control
available when the systems were first introduced in the early part of
the 20th century.

G.Harman

"John Williamson" wrote in message
...
On 28/07/2014 19:20, harryagain wrote:
"The Natural Philosopher" wrote in message
...
On 28/07/14 08:22, John Williamson wrote:
On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.


So, having taught grandmother to suck eggs, where is the power loss due
to
inductance?

The loss arises from energy taken to reverse the magnetic field.
https://en.wikipedia.org/wiki/Magnetic_hysteresis


Not in copper or aluminium wires.

Any magnetic field takes energy to establish or reverse it.
Magnetic fields are associated with any electric current.

"Andy Wade" wrote in message
...
On 28/07/2014 10:09, Tim Watts wrote:

I would say we might as well have 400V as 230V and more or less halve
the conductor sizes. Much more than that is getting silly though.

I'd vote for the standard domestic supply being 3x32 A (3-ph) instead of
1x100 A. Then we'd have the advantages of 3-phase for motors and
rectification, and could have 400 V appliances like cookers and showers
hooked-up with 2.5 or 4 mm^2 cables. Proposals now required for a compact
5-pin 16 A plug & socket...

--
Andy

There's nothing stopping you having that now.
The range of appliances available might be a bit limited to you.

"Brian Gaff" wrote in message
...
Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!

Brian

No that's incorrect.
Higher frequency = smaller physical sized motors & transformers but greater
losses.
Aircraft run on high frequency power to save weight.

On 28/07/14 22:25, Andy Wade wrote:
On 28/07/2014 10:09, Tim Watts wrote:

I would say we might as well have 400V as 230V and more or less halve
the conductor sizes. Much more than that is getting silly though.

I'd vote for the standard domestic supply being 3x32 A (3-ph) instead of
1x100 A. Then we'd have the advantages of 3-phase for motors and
rectification, and could have 400 V appliances like cookers and showers
hooked-up with 2.5 or 4 mm^2 cables. Proposals now required for a
compact 5-pin 16 A plug & socket...


I agree...

If you look at a commando plug/socket, the pins are well built but not
that much heavier than a 15A round pin plug.

So I do not see why you could not make a 3 phase version of a 15A plug
that fitted in at least a double backbox.

On Tuesday, July 29, 2014 7:53:51 AM UTC+1, harry wrote:
"Brian Gaff" wrote in message
...

Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!

No that's incorrect.
Higher frequency = smaller physical sized motors & transformers but greater
losses.
Aircraft run on high frequency power to save weight.

HF smpsu transformers have much lower copper losses & total losses than 50Hz iron lumps.


NT

On 29/07/14 08:27, wrote:
On Tuesday, July 29, 2014 7:53:51 AM UTC+1, harry wrote:
"Brian Gaff" wrote in message
...

Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!

No that's incorrect.
Higher frequency = smaller physical sized motors & transformers but greater
losses.
Aircraft run on high frequency power to save weight.

HF smpsu transformers have much lower copper losses & total losses than 50Hz iron lumps.


Actually they don't.



NT



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Tuesday, July 29, 2014 8:37:56 AM UTC+1, The Natural Philosopher wrote:
On 29/07/14 08:27, wrote:
On Tuesday, July 29, 2014 7:53:51 AM UTC+1, harry wrote:
"Brian Gaff" wrote in message
...

Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!

No that's incorrect.
Higher frequency = smaller physical sized motors & transformers but greater
losses.
Aircraft run on high frequency power to save weight.

HF smpsu transformers have much lower copper losses & total losses than 50Hz iron lumps.

Actually they don't.

They surely do. Why do you say they dont?


NT

"Nightjar \"cpb\"@" "insert my surname here wrote:
For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.

It would also be more difficult to use such cables for tying people up, or
as a garotte. But then they're more useful as a cosh. It's a tricky one,
this H&S lark...

Theo

On 28/07/2014 13:29, John Williamson wrote:
On 28/07/2014 08:23, harryagain wrote:


Where exactly is this arc drawn for 30 minutes and for what purpose.?


The arc *can* be drawn by using the DC charge stored in the cable. No
claim was made that it ever had been drawn either deliberately or
otherwise, though it's the kind of trick that installation engineers
have been known to pull as a joke, or that happens when things go wrong
when commissioning plant of this sort.


If you watch footage of repairs to 400 kV overhead lines (typically shot
from helicopters) you will see long and impressive arcs being drawn from
these for several seconds while they are brought down to earth potential.

On 29/07/2014 07:43, harryagain wrote:
"John Williamson" wrote in message
...
On 28/07/2014 19:20, harryagain wrote:
"The Natural Philosopher" wrote in message
...
On 28/07/14 08:22, John Williamson wrote:
On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.


So, having taught grandmother to suck eggs, where is the power loss due
to
inductance?

The loss arises from energy taken to reverse the magnetic field.
https://en.wikipedia.org/wiki/Magnetic_hysteresis


Not in copper or aluminium wires.

Any magnetic field takes energy to establish or reverse it.
Magnetic fields are associated with any electric current.


That's not what it says in the article you referred us to.

--
Tciao for Now!

John.

On 28/07/2014 15:14, The Natural Philosopher wrote:
On 28/07/14 13:31, newshound wrote:


But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

You are quite right, of course. But the term "dielectric loss" is the
one which CEGB trainers used to use when lecturing mixed classes of
mathematicians, physicists, and all types of engineer to explain why
pylons were the prefered method of transmission, with underground cables
the least desirable from the viewpoint of efficiency.

It's a convenient if not very precise shorthand.


Its not. It is plain WRONG because 'dielectric' losses are losses
incurred IN a dielectric due to it having e.g. resistance.

http://en.wikipedia.org/wiki/Dielectric_loss


Agreed. But this was in the days before wikipedia. The difference really
doesn't matter to graduate civil or mechanical engineers, while
physicists and electrical engineers would not need to have to have it
explained; at least in those days.

On 28/07/2014 10:39, Robin wrote:
That is the number of deaths and serious injuries in the UK every
year. Around 2.5 million people in the UK also receive a mains voltage
electric shock every year.

Figures from an Electrical Safety Council surveys which have long left
me a bit puzzled. As regards the 2.5m electric shocks, family etc I've
asked (who include people in work and retired, people with young
children, people in rented accommodation etc) don't seem to get shocks
at that rate. So I wonder who/where they are. And as regards "serious
in jury", they define that to include "severe pain" (and all whether or
not medical treatment required).


Once in 20 years among the adult population does not seem wildly out to
me. Especially if you include "tingles" from wet appliances, and even
more static shocks to those who cannot differentiate. But I do wonder
where the statistic comes from.