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Ideal electrical systems (just idle curiosity)
On 28/07/2014 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. Although you would likely burn/smoke that many to death instead ;-) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Ideal electrical systems (just idle curiosity)
charles 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. But you'd get absurdly high currents. That would fit nicely into the modern mindset then. Absurdity is all the rage when it comes to h & S. Bill |
Ideal electrical systems (just idle curiosity)
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. Is that in Doncaster, nationally, or world wide? Bill |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 03:43, Bill Wright wrote:
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. Is that in Doncaster, nationally, or world wide? 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. -- Colin Bignell |
Ideal electrical systems (just idle curiosity)
"David Paste" wrote in message ... Hello all. The world has a few differing domestic electrical standards, 100, 120, 240 volts, 50 and 60 Hz and so on. Industrial customers have yet more. Distribution via high voltage AC, and now DC in places. I understand why various areas of the world have these differences - due to historical reasons, etc. My question is that if we were to have a brand new electrical system, common to all areas, what would, or could, it be? Still AC? 300 volts? Different frequency? No real reason to ask other than idle curiosity. There's no complete answer as it depends on the size of the system. Higher voltage reduce transmission losses. DC reduces transmission losses too. (But requires more technogly) Higher frequncys increases losses but makes more compact motors and transformers possible. We are in the midst of a technological evolution when our powers systems will be linked to others abroad far more than at present, micro generation will be universal and we will have smart grid technology to control everything. |
Ideal electrical systems (just idle curiosity)
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? |
Ideal electrical systems (just idle curiosity)
"Nightjar "cpb"@" "insert my surname here wrote in message ... On 27/07/2014 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. Like the man says, although the problem is significantly greater under water. 30km is about the limit for AC transmission under water, which is why our links to the continent are HVDC. Even then, the cables are very specialised and there are IIRC only three manufacturers of HVDC underwater cables in the world. That is a limiting factor on how many offshore wind farms can be built, as they need HVDC underwater cable, the manufacturers have a limited capacity and well filled order books, while increasing capacity is not something that can be done overnight. Our main link to Europe is not underwater, it is via the channel tunnel. http://www.independent.co.uk/news/bu...l-2289665.html |
Ideal electrical systems (just idle curiosity)
On 28/07/14 02:04, The Natural Philosopher wrote:
On 27/07/14 23:46, Tim Watts wrote: On 27/07/14 22:24, Nightjar "cpb"@ insert my surname here 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. There would also be an advantage to choosing a lower frequency, which would reduce transmission losses (around 12% at lower voltages). The flicker effect of a lower frequency could be overcome by mandating only high frequency fluorescents or all LED lighting. That's going to be a big cable to my 3kW kettle and heater ;-) There's something to be said for higher voltage = lower current and a lower risk of fires. its about power not current High current = risk of terminations becoming hot and starting a fire. High current = larger cables that are more difficult to terminate properly. |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 02:06, The Natural Philosopher wrote:
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 The main AC losses are inductive and leakage by capacitance to ground, not resistive. That's what they told me when I took a group of trainee electrical engineers to the site a few decades ago. The guy was actually quite surprised when none of them could answer the question he asked of why they did it the way they do, but the coach driver could. Assuming the power *could* be usefully transmitted that far through an underground/ undersea cable, it wouldn't be much harder to lock the English and French grids than it is to lock the French, German, Italian and so on grids. -- Tciao for Now! John. |
Ideal electrical systems (just idle curiosity)
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. The capacitance per kilometre of overhead lines between cable and ground is low, while the capacitance per kilometre of underground cables is at least two orders of magnitude higher. At the lengths of cable used for power distribution, some of the effects that normally only affect HF signals come into play at 50Hz. -- Tciao for Now! John. |
Ideal electrical systems (just idle curiosity)
Bill Wright wrote:
charles 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. But you'd get absurdly high currents. That would fit nicely into the modern mindset then. Absurdity is all the rage when it comes to h & S. Bill And think of the size of the appliances and motors etc and the cost of the copper and the overall resources |
Ideal electrical systems (just idle curiosity)
"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. Where exactly is this arc drawn for 30 minutes and for what purpose.? |
Ideal electrical systems (just idle curiosity)
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. -- Colin Bignell |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 08:16, harryagain wrote:
"Nightjar "cpb"@" "insert my surname here wrote in message ... On 27/07/2014 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. Like the man says, although the problem is significantly greater under water. 30km is about the limit for AC transmission under water, which is why our links to the continent are HVDC. Even then, the cables are very specialised and there are IIRC only three manufacturers of HVDC underwater cables in the world. That is a limiting factor on how many offshore wind farms can be built, as they need HVDC underwater cable, the manufacturers have a limited capacity and well filled order books, while increasing capacity is not something that can be done overnight. Our main link to Europe is not underwater, it is via the channel tunnel. http://www.independent.co.uk/news/bu...l-2289665.html That is a quarter of the capacity of the Sellindge to Les Mandarins underwater link and they were still only talking about it in April this year. -- Colin Bignell |
Ideal electrical systems (just idle curiosity)
In article ,
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. but the higher currents involved could easily cause greater fire hazards - so an increase in fatalities . -- From KT24 Using a RISC OS computer running v5.18 |
Ideal electrical systems (just idle curiosity)
harryagain wrote:
Our main link to Europe is not underwater, it is via the channel tunnel. "IS" are you sure? http://www.independent.co.uk/news/bu...l-2289665.html I read lots of "PLANS", "PROPOSED", "WILL" and "COULD". Facts harry, you should try some ... ElecLink doesn't even seem to have started yet, and may never do http://www.ft.com/cms/s/0/2f563bce-9e1a-11e3-b429-00144feab7de.html#axzz38kOXxdkI Proposed capacity is 1000MW (doubled from the initial 500MW capacity you linked to), isn't the existing French connector 2000MW, and the existing Dutch connector 1000MW, how would that make it the main link? Seems they have greased enough palms as rules have now been bent for them https://www.ofgem.gov.uk/ofgem-publications/87163/eleclinkdecisioncoverletter.pdf |
Ideal electrical systems (just idle curiosity)
In article , The Natural Philosopher
scribeth thus 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.. Wouldn't have thought it would be but the article alluded to was very comprehensive as to the reasons why it was a problem... Seek ye here!... http://new.abb.com/about/technology/dc-portal -- Tony Sayer |
Ideal electrical systems (just idle curiosity)
In article , Andy
Burns scribeth thus harryagain wrote: Our main link to Europe is not underwater, it is via the channel tunnel. "IS" are you sure? http://www.independent.co.uk/news/bu...r-link-to-run- through-channel-tunnel-2289665.html I read lots of "PLANS", "PROPOSED", "WILL" and "COULD". Facts harry, you should try some ... ElecLink doesn't even seem to have started yet, and may never do http://www.ft.com/cms/s/0/2f563bce-9...ml#axzz38kOXxd kI Proposed capacity is 1000MW (doubled from the initial 500MW capacity you linked to), isn't the existing French connector 2000MW, and the existing Dutch connector 1000MW, how would that make it the main link? Seems they have greased enough palms as rules have now been bent for them https://www.ofgem.gov.uk/ofgem-publi...ncoverletter.p df This is how we're going to get around power shortages in the UK look too that forward thinking country France and pipe their nuclear power in by that tunnel!.. Now we know the real reason why it was built, perhaps theres a 4th bore there somewhere;?.... -- Tony Sayer |
Ideal electrical systems (just idle curiosity)
Tim Watts wrote:
High current = larger cables that are more difficult to terminate properly. and much more expensive, so people are likely to scrimp and use under-specced extensions ... |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 09:47, Andy Burns wrote:
Tim Watts wrote: High current = larger cables that are more difficult to terminate properly. and much more expensive, so people are likely to scrimp and use under-specced extensions ... The logical extension of those arguments is to put 11kV straight into the house :-) -- Colin Bignell |
Ideal electrical systems (just idle curiosity)
On Monday, July 28, 2014 8:22:28 AM UTC+1, F Murtz wrote:
Bill Wright wrote: charles 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. But you'd get absurdly high currents. That would fit nicely into the modern mindset then. Absurdity is all the rage when it comes to h & S. And think of the size of the appliances and motors etc and the cost of the copper and the overall resources Extra resource use would translate to less NHS funding and more deaths, not less, so perfect for the greenie brigade. The excessive copper use would also mean going to ali, so lots more fires. Electrical fires cause far more deaths than shock. One could in principle include either AFCIs or a heat sensitive resistive composite wire run along all conductors plus a basic bit of electronics. When temp rises unacceptably the thing switches off. Its all gobbling resources though, resources that would be far more constructively be spent elsewhere. At this time going higher V would make more sense than lower. NT |
Ideal electrical systems (just idle curiosity)
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 |
Ideal electrical systems (just idle curiosity)
On 28/07/14 09:50, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 09:47, Andy Burns wrote: Tim Watts wrote: High current = larger cables that are more difficult to terminate properly. and much more expensive, so people are likely to scrimp and use under-specced extensions ... The logical extension of those arguments is to put 11kV straight into the house :-) Not really - then it becomes equally dangerous and impractical. 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. |
Ideal electrical systems (just idle curiosity)
The logical extension of those arguments is to put 11kV straight into
the house :-) Aren't we allowed to score more Darwinian selection as a benefit? -- Robin reply to address is (meant to be) valid |
Ideal electrical systems (just idle curiosity)
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 -- From the Sofa of Brian Gaff Reply address is active "David Paste" wrote in message ... Hello all. The world has a few differing domestic electrical standards, 100, 120, 240 volts, 50 and 60 Hz and so on. Industrial customers have yet more. Distribution via high voltage AC, and now DC in places. I understand why various areas of the world have these differences - due to historical reasons, etc. My question is that if we were to have a brand new electrical system, common to all areas, what would, or could, it be? Still AC? 300 volts? Different frequency? No real reason to ask other than idle curiosity. Thanks in advance, David Paste. |
Ideal electrical systems (just idle curiosity)
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). -- Robin reply to address is (meant to be) valid |
Ideal electrical systems (just idle curiosity)
On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and the UK? No real reason why you couldn't make the channel link work using AC, there are a number of transmission lines, some with part undergrounded sections in the UK that are significantly longer overall. No true underwater AC connections though, the ones that do run underwater (on the grid system at least) all run in tunnels. However, the impact of a single point connection and the loss of that connection was more of a concern, hence the UK - France link is comprised of 2 x 1000MW links and the AC/DC conversion process permits presettable defined levels of power transfer regardless of most external conditions so the interconnector is essentially despatchable 'generation' at the entry point to the respective countries. There is also a degree of isolation from system disturbances when interconnecting at DC which can be very useful from a system stability point of view. -- |
Ideal electrical systems (just idle curiosity)
On Mon, 28 Jul 2014 08:16:50 +0100, "harryagain"
wrote: Our main link to Europe is not underwater, it is via the channel tunnel. http://www.independent.co.uk/news/bu...l-2289665.html The two HVDC links to Europe, the 1000MW UK-NED and te 200MW UK-FRA are both partly underwater, the latter in operation for the last 28 years. Neither use any part of the channel tunnel. -- |
Ideal electrical systems (just idle curiosity)
On Sun, 27 Jul 2014 22:33:37 +0100, "Nightjar \"cpb\"@" "insert my surname
here wrote: Like the man says, although the problem is significantly greater under water. 30km is about the limit for AC transmission under water, which is why our links to the continent are HVDC. Even then, the cables are very specialised and there are IIRC only three manufacturers of HVDC underwater cables in the world. That is a limiting factor on how many offshore wind farms can be built, as they need HVDC underwater cable, the manufacturers have a limited capacity and well filled order books, while increasing capacity is not something that can be done overnight. Some, but I'm not sure exactly what proportion of UK offshore wind farms have AC substations located offshore and an AC connection to the existing grid / distribution network. I can see DC being of use in the truly offshore arrays that Germany operates that are out of sight and over the horizon but for the UK wind farms that are located much closer to shore there seems little or no point in converting to DC. There is mention in this article clearly implying an AC connection and interconnection regime for the London Array the biggest of the white elephant monstrosities to pollute our country. http://www.theengineer.co.uk/sectors...012971.article There is a 600kV 2.2GW mainly underwater DC connection currently under construction between Scotland and the Wirral to carry the output from wind generation but this is a point to point grid connection with no directly connected generation. -- |
Ideal electrical systems (just idle curiosity)
On 28/07/14 10:40, The Other Mike wrote:
On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote: I thought it was more the issue that you cannot phase lock France and the UK? No real reason why you couldn't make the channel link work using AC, there are a number of transmission lines, some with part undergrounded sections in the UK that are significantly longer overall. No true underwater AC connections though, the ones that do run underwater (on the grid system at least) all run in tunnels. However, the impact of a single point connection and the loss of that connection was more of a concern, hence the UK - France link is comprised of 2 x 1000MW links and the AC/DC conversion process permits presettable defined levels of power transfer regardless of most external conditions so the interconnector is essentially despatchable 'generation' at the entry point to the respective countries. There is also a degree of isolation from system disturbances when interconnecting at DC which can be very useful from a system stability point of view. How are you going to phase lock the French Grid to the UK Grid? The "length" is a red herring... |
Ideal electrical systems (just idle curiosity)
"Nightjar "cpb"@" "insert my surname here wrote in message ... 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. I don't believe that with the difficulty of terminating the much thicker cables required with stuff like electric jugs etc. |
Ideal electrical systems (just idle curiosity)
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. The capacitance per kilometre of overhead lines between cable and ground is low, while the capacitance per kilometre of underground cables is at least two orders of magnitude higher. At the lengths of cable used for power distribution, some of the effects that normally only affect HF signals come into play at 50Hz. -- Everything you read in newspapers is absolutely true, except for the rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll |
Ideal electrical systems (just idle curiosity)
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? Seek ye here!... http://new.abb.com/about/technology/dc-portal -- Everything you read in newspapers is absolutely true, except for the rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll |
Ideal electrical systems (just idle curiosity)
On Mon, 28 Jul 2014 10:44:43 +0100, Tim Watts wrote:
On 28/07/14 10:40, The Other Mike wrote: On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote: I thought it was more the issue that you cannot phase lock France and the UK? No real reason why you couldn't make the channel link work using AC, there are a number of transmission lines, some with part undergrounded sections in the UK that are significantly longer overall. No true underwater AC connections though, the ones that do run underwater (on the grid system at least) all run in tunnels. However, the impact of a single point connection and the loss of that connection was more of a concern, hence the UK - France link is comprised of 2 x 1000MW links and the AC/DC conversion process permits presettable defined levels of power transfer regardless of most external conditions so the interconnector is essentially despatchable 'generation' at the entry point to the respective countries. There is also a degree of isolation from system disturbances when interconnecting at DC which can be very useful from a system stability point of view. How are you going to phase lock the French Grid to the UK Grid? The "length" is a red herring... 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. 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. 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. -- |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 09:21, Huge wrote:
On 2014-07-28, John Williamson wrote: On 28/07/2014 02:06, The Natural Philosopher wrote: 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 The main AC losses are inductive and leakage by capacitance to ground, not resistive. That's what they told me when I took a group of trainee electrical engineers to the site a few decades ago. The guy was actually quite surprised when none of them could answer the question he asked of why they did it the way they do, but the coach driver could. The coach driver had done the tour before ... No, the coach driver is the son of an electrical engineer who specialised in the heavy stuff, and had been playing with electronics since he was about 11 years old. -- Tciao for Now! John. |
Ideal electrical systems (just idle curiosity)
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. 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? -- Tciao for Now! John. |
Ideal electrical systems (just idle curiosity)
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. |
Ideal electrical systems (just idle curiosity)
On 28/07/2014 10:42, The Other Mike wrote:
On Mon, 28 Jul 2014 08:16:50 +0100, "harryagain" wrote: Our main link to Europe is not underwater, it is via the channel tunnel. http://www.independent.co.uk/news/bu...l-2289665.html The two HVDC links to Europe, the 1000MW UK-NED and te 200MW UK-FRA are both partly underwater, the latter in operation for the last 28 years. Neither use any part of the channel tunnel. Don't confuse him with facts, or it'll all end in tears. -- Tciao for Now! John. |
Ideal electrical systems (just idle curiosity)
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. -- Tciao for Now! John. |
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