On 13/03/18 15:55, NY wrote:
"Tim Streater" wrote in message
.. .
In article , NY
wrote:

"The Natural Philosopher" wrote in message
news On 13/03/18 12:13, NY wrote:
What were the reasons for the UK having its own grid, with a *DC*
connection to mainland Europe? Was it just that the UK wasn't part
of Europe at the time, or was there another more technical, less
political reason?

Well you see its this odd and not very political thing called
GEOGRAPHY. You maye have heard of it although its not as fashoinable
as gay marriage, but what it means is that if you walked all round
the COAST like that ponce on TV you find that is water on every side!

And that means its a long way to string pylons in shipping lanes so
teh GB grid is naturally isolated and always was, since ints
inception in IIRC the 1930s

Yes, that's a very good reason for not having *any* connection
between UK and mainland Europe.

No, you run it on the seabed, or perhaps through the tunnel.

But given that there *is* a connection, is there a reason why it is
DC rather than AC?

Capacitance losses.

Ah. Yes that makes sense. 20 miles of overhead line would be fine (*)
but 20 miles of coaxial cable will have significant capacitance.

Its not coaxial I think, well only in the sense that the sea forms the
outer conductor, together with the armor..

http://www.caledonian-cables.com/pro...es/XLPE-Dc.jpg

is my understanding of a link. I am not sure whether a return cable is
provided or whether the sea does that job





As a matter of interest, how do they avoid the problem when overhead
lines are converted to run underground, eg when passing through an area
of outstanding natural beauty?

Or oustide my door


Do underground lines run as a single cable with three conductors (for
three phases)

yes

surrounded by a common earth,

no. There is no earth on 3 phase usually - ir maybe they use the armour
for that.


or are they three separate
lines, each with its own earth screen? Indeed is it necessary to have an
earth screen as long as the wires are suitably insulated?


Sometimes. It just depends on local conditions



(*) Apart from the "little" matter of suspending the wires across the
Channel :-)


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"The Natural Philosopher" wrote in message
news
Ah. Yes that makes sense. 20 miles of overhead line would be fine (*) but
20 miles of coaxial cable will have significant capacitance.

Its not coaxial I think, well only in the sense that the sea forms the
outer conductor, together with the armor..

http://www.caledonian-cables.com/pro...es/XLPE-Dc.jpg

is my understanding of a link. I am not sure whether a return cable is
provided or whether the sea does that job

According to https://en.wikipedia.org/wiki/HVDC_Cross-Channel, " there is no
provision to permit neutral current to flow through the sea" and the cable
is bipolar which I interpret as being two wires at +/- half the total
voltage wrt to earth. And "although each station includes an earth
electrode, this is used only to provide a neutral reference, and only one of
the two electrodes is connected at a given time so that there can be no
current flow between them."

I presume if the cables were transmitting AC and were to be widely
separated, the capacitive effects between them could be made negligible but
the capacitive effect wrt earth would not be - and I imagine that water
makes a better dielectric than air, which is why wires strung between pylons
in the air don't suffer the same losses as cables buried in(and insulated
from) water.

Interesting. I'd always thought that the purpose of the DC link was to
isolate the frequency/phase of the UK system from the European system, but
it seems that this is a by-product of the main purpose of avoiding
capacitive losses.

So that's two things I've learned in the last few days:

- why the UK is not AC-linked to Europe

- that even modern clocks may still use the mains frequency as a time source
and that it's not only synchronous motors in mechanical clocks that use
this, and that not all mains digital clocks use their own quartz crystal.

On 13/03/18 17:46, NY wrote:
I presume if the cables were transmitting AC and were to be widely
separated, the capacitive effects between them could be made negligible
but the capacitive effect wrt earth would not be - and I imagine that
water makes a better dielectric than air, which is why wires strung
between pylons in the air don't suffer the same losses as cables buried
in(and insulated from) water.

Yes. That's the issue - capacity to earth.


Interesting. I'd always thought that the purpose of the DC link was to
isolate the frequency/phase of the UK system from the European system,
but it seems that this is a by-product of the main purpose of avoiding
capacitive losses.

Yup. And very handy it is too.


--
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always run out of other people's money. It's quite a characteristic of them"

Margaret Thatcher

James Wilkinson Sword wrote:

On Sat, 10 Mar 2018 21:01:10 -0000, Roger Hayter wrote:

James Wilkinson Sword wrote:

On Sat, 10 Mar 2018 09:36:36 -0000, Chris J Dixon
wrote:

The Natural Philosopher wrote:

I thought electric trains connect(ed) their motors in parallel mode to
start off, which is why they always (used to) start with a jerk.

Series, more like, to limit current.

That's right, start in series, then later switch to parallel.

Jerk is just the inability to reduce it ENOUGH.

Quite so. Until the advent of power electronics in rail traction,
then control was generally either by tapchanger, for ac supplies,
or series resistors for dc schemes. In both cases the steps (or
notches as they are known) are finite, not continuously variable,
and there will always be jerks. The art of the design engineer is
making them as smooth as practicable.

Somewhere in the loft I have the notching curves I drew for the
Class 313 rolling stock.

I wish someone would put soft start onto conveyor belts in supermarkets.
Actually it is kinda funny to put milk or bottles of vodka upright then
laugh when the supermarket has to replace them for free.


I expect they sometimes wish the mentally subnormal had minders to tell
them to put glass bottles on their sides.

So they roll into the next person's food. Why not just make the motor
work properly? This is the 21st century.

You keep saying that. It would not be simple or cheap. At the moment
you just need a crude set of rollers and bearings, and a sufficiently
powerful motor to overcome limiting friction at maximum torque. You
would need some combination of better bearings for the belt rollers,
more precision and rigidity of the whole conveyor structure, a much
larger motor with either a variable frequency inverter or a continuously
variable gearbox. And a control system to replace the current on/off
switch in the mains supply. If you don't believe me, try and make one
yourself.

--

Roger Hayter

On 13/03/2018 19:44, James Wilkinson Sword wrote:
On Tue, 13 Mar 2018 19:18:20 -0000, Roger Hayter wrote:

James Wilkinson Sword wrote:

On Sat, 10 Mar 2018 21:01:10 -0000, Roger Hayter
wrote:

James Wilkinson Sword wrote:

On Sat, 10 Mar 2018 09:36:36 -0000, Chris J Dixon

wrote:

The Natural Philosopher wrote:

I thought electric trains connect(ed) their motors in parallel
mode to
start off, which is why they always (used to) start with a jerk.

Series, more like, to limit current.

That's right, start in series, then later switch to parallel.

Jerk is just the inability to reduce it ENOUGH.

Quite so. Until the advent of power electronics in rail traction,
then control was generally either by tapchanger, for ac supplies,
or series resistors for dc schemes. In both cases the steps (or
notches as they are known) are finite, not continuously variable,
and there will always be jerks. The art of the design engineer is
making them as smooth as practicable.

Somewhere in the loft I have the notching curves I drew for the
Class 313 rolling stock.

I wish someone would put soft start onto conveyor belts in
supermarkets.
Actually it is kinda funny to put milk or bottles of vodka upright
then
laugh when the supermarket has to replace them for free.


I expect they sometimes wish the mentally subnormal had minders to
tell
them to put glass bottles on their sides.

So they roll into the next person's food.* Why not just make the motor
work properly?* This is the 21st century.

You keep saying that.* It would not be simple or cheap.* At the moment
you just need a crude set of rollers and bearings, and a sufficiently
powerful motor to overcome limiting friction at maximum torque.** You
would need some combination of better bearings for the belt rollers,
more precision and rigidity of the whole conveyor structure, a much
larger motor with either a variable frequency inverter or a continuously
variable gearbox.* And a control system to replace the current on/off
switch in the mains supply.** If you don't believe me, try and make one
yourself.

No, you take the current system and add a soft start thyristor like on a
washing machine.* Five quid maybe?* Jesus Christ my £30 cordless drill
can do it.

With widely variable friction from the crude conveyor mechanism?

--
Max Demian

On Tue, 13 Mar 2018 19:18:20 +0000, Roger Hayter, the idiotic troll-feeding
Brit, wrote:


So they roll into the next person's food. Why not just make the motor
work properly? This is the 21st century.

You keep saying that.

No, Brit twit, he doesn't say that! He keeps successfully BAITING you, you
rare idiot!

On Tue, 13 Mar 2018 20:05:10 +0000, Max Demian wrote:


With widely variable friction from the crude conveyor mechanism?

You guys KNOW what's wrong with the Scottish sow, don't you?

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On 13/03/18 19:18, Roger Hayter wrote:
So they roll into the next person's food. Why not just make the motor
work properly? This is the 21st century.
You keep saying that. It would not be simple or cheap. At the moment
you just need a crude set of rollers and bearings, and a sufficiently
powerful motor to overcome limiting friction at maximum torque. You
would need some combination of better bearings for the belt rollers,
more precision and rigidity of the whole conveyor structure, a much
larger motor with either a variable frequency inverter or a continuously
variable gearbox. And a control system to replace the current on/off
switch in the mains supply. If you don't believe me, try and make one
yourself.
All you need is a sort of visvoius clutch, or possibly a flywheel, to
smooth out jerkiness. And then move the sensor a bit upstream


BUT how will that improve profits?


--
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On 13/03/2018 20:05, Max Demian wrote:

No, you take the current system and add a soft start thyristor like on
a washing machine.* Five quid maybe?* Jesus Christ my £30 cordless
drill can do it.

With widely variable friction from the crude conveyor mechanism?

Sure. You need servo feedback so the drive computer knows how fast the
belt is going. You might be right about the 5 quid - but that's 5 quid
on every belt in every store. It would probably be less reliable too.

There's just not a good enough reason.

Andy

On Thu, 15 Mar 2018 21:38:48 +0000, James Wilkinson Sword wrote:

I've lost count of how many times
someone's Pimms has fallen off and smashed, at the store's expense.
Would you buy a car that only went 0mph and 50mph?


you dont half talk some ****e

In article ,
James Wilkinson Sword wrote:
It only takes one damaged product to cost them a fiver. The current
ones are not fit for purpose. I've lost count of how many times
someone's Pimms has fallen off and smashed, at the store's expense.

You must live beside some very clumsy people. Who seem only to buy boose.
Perhaps the two are related.

--
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On Fri, 16 Mar 2018 00:29:53 +0000 (GMT), Dave Lowman (News) wrote:


You must live beside some very clumsy people. Who seem only to buy boose.
Perhaps the two are related.

You must be even dumber than suspected, continually feeding the filthiest
and most idiotic troll around! tsk

On Tue, 13 Mar 2018 12:13:50 -0000, "NY" wrote:


What were the reasons for the UK having its own grid, with a *DC* connection
to mainland Europe? Was it just that the UK wasn't part of Europe at the
time, or was there another more technical, less political reason?


Yes, see

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