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Supply voltage to overhead 240V mains wiring transformer
As a matter of interest, what's the typical voltage of the three wires
connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? |
Supply voltage to overhead 240V mains wiring transformer
On 01/09/2015 10:55, NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! |
Supply voltage to overhead 240V mains wiring transformer
NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? https://en.wikipedia.org/wiki/Distribution_transformer |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 1 Sep 2015 11:20:14 +0100, newshound wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! 11 kV is the normal distribution voltage to end users from a Primary substation (pole transformers are classed as "sub-stations"). The Primary substation will probably be fed at 33 kV or higher depending on how big it is. It will almost certainly have at least two feeds, main and reserve. The reserve to the Primary substation here is 11 kV, the main 33 kV. What haapens on the 240 V side varies greatly, it can be 4 wire (3 phases, Neutral and Earth) any single phase supplied property taking a phase N and E. Down to two wire, phase and combined Neutral/Earth, this is what our supply is. The Neutral is bonded to physical ground at the pole. -- Cheers Dave. |
Supply voltage to overhead 240V mains wiring transformer
"charles" wrote in message
... In article , newshound wrote: On 01/09/2015 10:55, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! It certainly used to be 11kV. However, my working time with an Electricity Board was in 1959. Given that supply voltages are multiples of 11 (11 kV, 33 kV, 132 kV), I wonder why OHLE railway electrification standardised on 25 kV rather than 22 kV? |
Supply voltage to overhead 240V mains wiring transformer
On 9/1/2015 7:00 AM, Huge wrote:
On 2015-09-01, newshound wrote: On 01/09/2015 10:55, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! The ones of a similar description coming to my house are 11kV. Mine, too. |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 01 Sep 2015 12:19:52 +0100 (BST), "Dave Liquorice"
wrote: I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! 11 kV is the normal distribution voltage to end users from a Primary substation (pole transformers are classed as "sub-stations"). Diverging off the topic slightly I know of a couple who having decided on an "Escape to the Country " inspired move avoided looking at some d properties due to the descriptions mentioning a "Sub-Station" nearby. It was only later in the search process that they discovered not all things described as a sub station looked like a large brick and concrete box with a numerous conductors and insulators like they often saw from the train to work and the "Sub -Stations" concerned were the pole transformers for the property and sometimes some others nearby. G.Harman |
Supply voltage to overhead 240V mains wiring transformer
In article , NY
wrote: "charles" wrote in message ... In article , newshound wrote: On 01/09/2015 10:55, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! It certainly used to be 11kV. However, my working time with an Electricity Board was in 1959. Given that supply voltages are multiples of 11 (11 kV, 33 kV, 132 kV), I wonder why OHLE railway electrification standardised on 25 kV rather than 22 kV? Rail electrical supply is single phase. The distribution supplies are 3 phase. -- Please note new email address: |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 1 Sep 2015 08:51:38 -0400, S Viemeister wrote:
I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! The ones of a similar description coming to my house are 11kV. Mine, too. Good grief what do you two do to have 11 kV in the house? The supply here is 1 phase 240 V to the house from the 11 kV sub-station up a pole 10 yards from the house... -- Cheers Dave. |
Supply voltage to overhead 240V mains wiring transformer
On Tuesday, September 1, 2015 at 10:55:02 AM UTC+1, NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? It's most likely to be 11kv. It could be 6.6kv 11kv or even very rarely 33v in the UK. It will be delta connected on the primary side. Some rural properties only get two phases on the primary side. Not in the UK, but in some countries abroad the primary side can be a single phase and the return is via the earth. On the secondary there are multiple configurations. It will be star connected. Earth may or may not be combined with neutral on a single conductor or not supplied at all. There may be a single phase, two phases or three phases. Some remote locations have a split phase arrangement on the secondary where the supply is a single phase centre grounded. This allows a supply a little bit more remote from a single phase supplied transformer. The neutral will be earthed at the substation. A combined earth and neutral conductor should be earthed at multiple points along the route. If the load were balanced completely there will be no current on the neutral conductor. In practice there will be current on the neutral conductor but it should not exceed the current on a single phase - it would take a very odd inductive load to do that. Don't use this info for anything other than entertainment. I may be talking out of my arse. Philip |
Supply voltage to overhead 240V mains wiring transformer
On 01/09/15 10:55, NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". 11KV I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? If it IS done that way the currents should cancel out.. -- New Socialism consists essentially in being seen to have your heart in the right place whilst your head is in the clouds and your hand is in someone else's pocket. |
Supply voltage to overhead 240V mains wiring transformer
On 01/09/15 11:20, newshound wrote:
On 01/09/2015 10:55, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! 3.3kV and 6.6kV are also possible - but 33kV seems a quite common option for a "whole district" type feed. |
Supply voltage to overhead 240V mains wiring transformer
On 01/09/15 20:32, Tim Watts wrote:
On 01/09/15 11:20, newshound wrote: On 01/09/2015 10:55, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! 3.3kV and 6.6kV are also possible - but 33kV seems a quite common option for a "whole district" type feed. And I'll quickly qualify that - 33kV is normally dropped to 11kV then fed round the local HV circuits to the 230/400V transformers. |
Supply voltage to overhead 240V mains wiring transformer
wrote in message
... If the load were balanced completely there will be no current on the neutral conductor. In practice there will be current on the neutral conductor but it should not exceed the current on a single phase - it would take a very odd inductive load to do that. Like pikeys pinching a bit of copper that they think is an earth when it is a neutral on a three phase supply. -- Adam |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 01 Sep 2015 10:55:01 +0100, NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? Without bothering to look at all the other replies, I can tell you that a 3 phase with neutral LV distribution cabling system between the 240v substation and domestic properties only subjects the neutral to a maximum current equal to that of any of the phases in a worst case scenario (either only one or two of the phases supplying their maximum rated currents with either the other two or one disconnected). When all three phases are supplying a balanced 3 phase loading, no current flows in the common neutral back to the substation transformer. However, for each connected property, the neutral will carry the return current to the street joint onto the 3 phase supply distribution cabling where it will be cancelled out to a greater or lesser degree by the neutral return currents of adjacent properties fed from the other two phases. There will be some current flowing between the tapping off points along the street distribution 3 phase plus neutral cable but it will never exceed, even in the worst case, the currents carried by any one phase. Compared to a simple single phase distribution using only two wires in the street distribution cabling where each conductor has to be able to safely carry 3 times the current of each phase wire in the 3 phase system, there is a significant saving in copper investment (a 33% reduction in copper costs) plus, as a bonus, elimination of volt drop in the common neutral return under maximum balanced loading conditions. As far as the rural distribution system with pole transformers that you've described, I believe the voltage level on these lines is typically 6 or 11 KV (I'm not an expert on such rustic arrangements - 11KV is a common voltage level and I have a vague recollection of 6KV being mentioned). The common neutral on an 11 or 6KV line cannot be used directly by the connected properties. Each property's neutral simply terminates on the neutral connection of the pole transformer's LV secondary (where it may meet neutral connections from two other adjacent properties if within reaching distance of the LV overhead cabling). It is my understanding that the neutral connection on the LV secondary will be independently connected to a local earthing spike or spikes provided by the utility company responsible for the supply. It may not be as good a low earth resistance connection as that provided in urban substations but it'll be a damn sight safer than relying on an 11 or 6 KV distribution neutral connection (assuming such a connection is provided or even needed in the higher voltage levels of the distribution network). I'm now going to hit send and take a look at what the 'experts' have said and see how big a fool I may have made of myself. :-) -- Johnny B Good |
Supply voltage to overhead 240V mains wiring transformer
In message , Huge
writes On 2015-09-01, Dave Liquorice wrote: On Tue, 1 Sep 2015 08:51:38 -0400, S Viemeister wrote: I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! The ones of a similar description coming to my house are 11kV. Mine, too. Good grief what do you two do to have 11 kV in the house? Oh, I don't. We have an ugly grey box up a pole about 50 yards away, where the 11kV goes down to 240V. When I say "to my house", I mean we're the only house on it. I think they look rather nice. Https://www.dropbox.com/s/03z4oruxg7...54.41.jpg?dl=0 https://www.dropbox.com/s/2zn9fv7cmz...55.05.jpg?dl=0 One I found ready to go up a pole near Stranraer. They are indeed 11KV in 240V out Brian -- Brian Howie |
Supply voltage to overhead 240V mains wiring transformer
Brian Howie wrote:
https://www.dropbox.com/s/2zn9fv7cmz...55.05.jpg?dl=0 One I found ready to go up a pole near Stranraer. They are indeed 11KV in 240V out Was that a still from a video, or does the engraving/printing on the plate have interlaced 'mice teeth'' on it? |
Supply voltage to overhead 240V mains wiring transformer
In article ,
Brian Howie wrote: In message , Huge writes On 2015-09-01, Dave Liquorice wrote: On Tue, 1 Sep 2015 08:51:38 -0400, S Viemeister wrote: I thought they were 11 kV or 33 kV but someone who knows will be along in a minute! The ones of a similar description coming to my house are 11kV. Mine, too. Good grief what do you two do to have 11 kV in the house? Oh, I don't. We have an ugly grey box up a pole about 50 yards away, where the 11kV goes down to 240V. When I say "to my house", I mean we're the only house on it. I think they look rather nice. Https://www.dropbox.com/s/03z4oruxg7...54.41.jpg?dl=0 https://www.dropbox.com/s/2zn9fv7cmz...55.05.jpg?dl=0 One I found ready to go up a pole near Stranraer. They are indeed 11KV in 240V out have they really made 11111316037 of them? -- Please note new email address: |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 01 Sep 2015 22:08:45 GMT, Johnny B Good wrote:
It is my understanding that the neutral connection on the LV secondary will be independently connected to a local earthing spike or spikes provided by the utility company responsible for the supply. It may not be as good a low earth resistance connection as that provided in urban substations but it'll be a damn sight safer than relying on an 11 or 6 KV distribution neutral connection (assuming such a connection is provided or even needed in the higher voltage levels of the distribution network). If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. With a signle phase transformer one side will be connected to a real earth connection at the pole, in our case it looks like a bit of 25 mm^2 before it disappears behind the protective capping and under ground. This earth may or may not be carried on a seperate wire into the house, around here the pole to house connection is mainly just two wire, phase and neutral earth combined. I'm now going to hit send and take a look at what the 'experts' have said and see how big a fool I may have made of myself. :-) The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. -- Cheers Dave. |
Supply voltage to overhead 240V mains wiring transformer
On Wed, 02 Sep 2015 14:39:26 +0100, Dave Liquorice wrote:
On Tue, 01 Sep 2015 22:08:45 GMT, Johnny B Good wrote: It is my understanding that the neutral connection on the LV secondary will be independently connected to a local earthing spike or spikes provided by the utility company responsible for the supply. It may not be as good a low earth resistance connection as that provided in urban substations but it'll be a damn sight safer than relying on an 11 or 6 KV distribution neutral connection (assuming such a connection is provided or even needed in the higher voltage levels of the distribution network). If you ever wander out in the the countryside and look at the 11 kV power distribution it's all three wire, just the three phases. With a single phase transformer one side will be connected to a real earth connection at the pole, in our case it looks like a bit of 25 mm^2 before it disappears behind the protective capping and under ground. This earth may or may not be carried on a seperate wire into the house, around here the pole to house connection is mainly just two wire, phase and neutral earth combined. I'm now going to hit send and take a look at what the 'experts' have said and see how big a fool I may have made of myself. :-) The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. I had an idea that the "LV" upper limit was a little bit more inclusive than the 240v house supply voltage level. I just wasn't too sure whether "LV" included 33KV as well as 11KV. I mentioned "LV" in the context of 240v to emphasise the fact that despite its potential for electrocution, 240v wasn't considered to be a high voltage by the Public Supply Utilities (PSUs). Still, if that's the only 'glaring error' in my 'pre-google to confirm the facts' posting, I don't think I made too big a fool of myself. :-) BTW, the sight of only 3 wires on rural 11/33KV transmission lines was also my recollection too but I've even seen 11/33KV lines strung with just two wires on rare occasions which left me a little bit puzzled to say the least. Googling suggests these 2 wire lines might possibly be examples of a bi- phase SWER transmission line (or, more likely here in the UK, just a simple 2 wire single phase spur to a remote load not deemed worthy of the expense of a 3 phase supply). -- Johnny B Good |
Supply voltage to overhead 240V mains wiring transformer
In article ,
Huge wrote: On 2015-09-02, Dave Liquorice wrote: [22 lines snipped] The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. 33kV is HV, according to the man from the 'leccy. The farm next door is being demolished and when the bloke from the 'leccy turned up to disconnect its electricity (& put in a 240V drop for the builders) he refused to go anywhere near the 33kV "because it was HV". [Snip] He was correct BS 7671:2008 aka The Wiring regs states: Extra-low. Not exceeding 50V ac or 120V ripple free DC Low. Exceeding extra-low but not exceeding 1000 v ac or 1500 V dc between conductors or 600V ac or 900V dc between conductors and earth High Exceeding low voltage. -- Please note new email address: |
Supply voltage to overhead 240V mains wiring transformer
In article ,
Johnny B Good wrote: On Wed, 02 Sep 2015 14:39:26 +0100, Dave Liquorice wrote: On Tue, 01 Sep 2015 22:08:45 GMT, Johnny B Good wrote: It is my understanding that the neutral connection on the LV secondary will be independently connected to a local earthing spike or spikes provided by the utility company responsible for the supply. It may not be as good a low earth resistance connection as that provided in urban substations but it'll be a damn sight safer than relying on an 11 or 6 KV distribution neutral connection (assuming such a connection is provided or even needed in the higher voltage levels of the distribution network). If you ever wander out in the the countryside and look at the 11 kV power distribution it's all three wire, just the three phases. With a single phase transformer one side will be connected to a real earth connection at the pole, in our case it looks like a bit of 25 mm^2 before it disappears behind the protective capping and under ground. This earth may or may not be carried on a seperate wire into the house, around here the pole to house connection is mainly just two wire, phase and neutral earth combined. I'm now going to hit send and take a look at what the 'experts' have said and see how big a fool I may have made of myself. :-) The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. I had an idea that the "LV" upper limit was a little bit more inclusive than the 240v house supply voltage level. I just wasn't too sure whether "LV" included 33KV as well as 11KV. I mentioned "LV" in the context of 240v to emphasise the fact that despite its potential for electrocution, 240v wasn't considered to be a high voltage by the Public Supply Utilities (PSUs). Still, if that's the only 'glaring error' in my 'pre-google to confirm the facts' posting, I don't think I made too big a fool of myself. :-) BTW, the sight of only 3 wires on rural 11/33KV transmission lines was also my recollection too but I've even seen 11/33KV lines strung with just two wires on rare occasions which left me a little bit puzzled to say the least. Googling suggests these 2 wire lines might possibly be examples of a bi- phase SWER transmission line (or, more likely here in the UK, just a simple 2 wire single phase spur to a remote load not deemed worthy of the expense of a 3 phase supply). there are quite a few of the in what used to be NSHEB territory. -- Please note new email address: |
Supply voltage to overhead 240V mains wiring transformer
On 02/09/15 14:39, Dave Liquorice wrote:
If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. Round here there are a few short single phase 11KV links - typically to a single property or a couple. -- New Socialism consists essentially in being seen to have your heart in the right place whilst your head is in the clouds and your hand is in someone else's pocket. |
Supply voltage to overhead 240V mains wiring transformer
On Tue, 01 Sep 2015 10:55:01 +0100, NY wrote:
As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? Having had some feedback and googled to verify 'my facts', I've decided to revisit your questions. Your mention of glass insulators and pole top transformers (mini sub- stations) rather implies an 11KV distribution[1] which doesn't normally include the neutral wire at this Medium Voltage level. The transformers employed are normally delta/wye types where the 11KV primary is delta connected, obviating the need for a neutral connection, with a wye connected 240v secondary to provide a locally grounded neutral return for each customer connection. Your concern over the rating of the neutral wire only applies when the sub-station transformer is at the remote end of a 240v LV 3 phase distribution cabling network (either underground in urban areas or else on poles in more rustic areas where you may well see all four wires strung from pole to pole). If your property is fed from a pole transformer (possibly also serving two neighbouring properties), it seems unlikely that the 11KV line will include a neutral wire. Otoh, if your incoming supply is via a drop line from an overhead LV 3 phase line from a remote sub-station transformer, your connection will simply be a live and neutral 2 wire drop connecting to the common neutral and one of the three phase wires. If you care to walk the route of such an LV line, close observation will reveal that every property connects to the neutral (usually the topmost or bottommost of the four wires) and one phase wire, usually in a cyclic sequence so that each phase wire only connects to every third property. If you're observant enough, you may also spot that the neutral is no thicker than any of the other 3 phase wires (indeed, if the phase wires are insulated, you might gain the impression that the neutral is thinner than the phase wires). Your surmise that under balanced loading conditions on all 3 phases that the neutral return current is cancelled out is quite correct. What's important in this case is that even under the most extreme conditions of unbalanced loading conditions, the neutral has to carry no more load current than any of the phase wires, hence it being sized exactly the same as the phase wires. [1] 11KV is the usual voltage level in this part of the distribution network but lower medium voltages might also be used such as 3.3 and 6.6 KV. Not as high as the more usual 11KV but still high enough to warrant 'glass insulators' and elimination of a neutral wire, courtesy of the pole transformer's delta primary windings connection topology. -- Johnny B Good |
Supply voltage to overhead 240V mains wiring transformer
On Wed, 02 Sep 2015 14:39:26 +0100 (BST), "Dave Liquorice"
wrote: If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. It's not all 3 wire ,we had a two wire 11kV line over our fields which served us and two other properties, in fact they were served first when it arrived in 1960 ,as Dad had bought a new generator a few years before and wanted to see some use out of it so we didn't connect till 1964. This branched off a 3 wire about 3/4 of a mile away, a similar 2 wire went in another direction but the two only shared one of the 3 wires in common so that was probably an attempt to keep the load reasonably balanced. They had to run another four poles to carry our 250V supply, each had an earth connection to the neutral with a red metal plate on each pole with PME in white letters on it, as a curious youngster I asked what that meant so became aware of what a protective multiple earth was when quite young. With a signle phase transformer one side will be connected to a real earth connection at the pole, in our case it looks like a bit of 25 mm^2 before it disappears behind the protective capping and under ground. This earth may or may not be carried on a seperate wire into the house, around here the pole to house connection is mainly just two wire, phase and neutral earth combined. G.Harman |
Supply voltage to overhead 240V mains wiring transformer
/Having had some feedback and googled to verify 'my facts', I/q MASSIVE SNIP
FFS? Jim K |
Supply voltage to overhead 240V mains wiring transformer
On Wed, 2 Sep 2015 17:07:36 +0100, The Natural Philosopher wrote:
If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. Round here there are a few short single phase 11KV links - typically to a single property or a couple. Yeah OK wrong word "all", we are on a two wire spur... But the two wire feeds are two of the phases from the main three phase (wire) distribution not a phase and neutral/earth. -- Cheers Dave. |
Supply voltage to overhead 240V mains wiring transformer
On 02/09/15 18:52, Dave Liquorice wrote:
On Wed, 2 Sep 2015 17:07:36 +0100, The Natural Philosopher wrote: If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. Round here there are a few short single phase 11KV links - typically to a single property or a couple. Yeah OK wrong word "all", we are on a two wire spur... But the two wire feeds are two of the phases from the main three phase (wire) distribution not a phase and neutral/earth. Yes. Of course. But that is in and of itself a 'single phase'... -- New Socialism consists essentially in being seen to have your heart in the right place whilst your head is in the clouds and your hand is in someone else's pocket. |
Supply voltage to overhead 240V mains wiring transformer
On 3 Sep 2015 09:31:25 GMT, Huge wrote:
S'what we're on. If you follow our 2 wire overhead a couple of miles (it runs alongside a favourite bridle way) it goes through some switchgear (operable from the ground, although padlocked) and then connects to two of the three phases of a three phase line. My memory might have got it wrong but I think I was told by an electricity board employee that type of switch wasn't designed to be operated under load but was operated when the line was dead and was for isolation of that spur after which the power on the feed was restored.This came up in a conversation about 45 years ago when some friends and I were caught by said employee who just happened to be passing at the time when my friends and I were lexamining the padlock for the isolator that controlled the feed to our school. Of course it was possible he deliberately misinformed us to discourage us doing it later. G.Harman |
Supply voltage to overhead 240V mains wiring transformer
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Supply voltage to overhead 240V mains wiring transformer
In message , Andy
Burns writes Brian Howie wrote: https://www.dropbox.com/s/2zn9fv7cmz...55.05.jpg?dl=0 One I found ready to go up a pole near Stranraer. They are indeed 11KV in 240V out Was that a still from a video, or does the engraving/printing on the plate have interlaced 'mice teeth'' on it? Not a video, It was a bit windy, maybe camera shake. Brian -- Brian Howie |
Supply voltage to overhead 240V mains wiring transformer
"Huge" wrote in message
... On 2015-09-02, charles wrote: In article , Huge wrote: On 2015-09-02, Dave Liquorice wrote: The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. 33kV is HV, according to the man from the 'leccy. The farm next door is being demolished and when the bloke from the 'leccy turned up to disconnect its electricity (& put in a 240V drop for the builders) he refused to go anywhere near the 33kV "because it was HV". Well, I wasn't about to argue with him about it. And there's no way I'm going anywhere near 33kV no matter what the regs say! I'd tend to regard "low voltage" as "definitely capable of being felt but not lethal", and "high voltage" as a voltage that you have some chance of surviving an electric shock from. 240V mains gives you a very nasty belt (I still have the scars on the first knuckle of my right index finger from when I brushed it against the terminals of an on-off switch in a tape recorder in my teens, after I forgot to unplug it, and I had to surreptitiously clean up my puddle of wee from the bedroom carpet). And then apply various levels of "extra high", "super high", "extremely high" adjectives beyond that! 650 V from a third rail would give you very nasty burns and probably kill you. And 25 kV from overhead line train electrification, or 11, 33, 275 or 400 kV from pylon wires, would probably set you alight as well. I lodged with a couple after I started my first job, and Mick worked as an emergency call-out engineer for one of the electricity companies. I remember he came back late one night, very shocked (pardon the unintentional pun) after having to clear up from an incident in which a JCB operator had plunged his bucket into a 400 kV underground cable. The JCB had melted and twisted so they had to saw it up to get the body of the guy out - and only then could they start to repair the cable. I take my hat off to the guys who work on pylon wires, firstly at great height and secondly while the lines are still live, in specially insulated cherry-pickers. |
Supply voltage to overhead 240V mains wiring transformer
On Wed, 02 Sep 2015 14:39:26 +0100, Dave Liquorice wrote:
The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. In the CAT system for grading the safety of DVMs, I often see the term (for CAT IV) "The source of the low voltage installation" and (CAT II) "The circuits directly connected to the low voltage installation." What is meant by "low voltage installation" in this context exactly? Sounds a very ambiguous. |
Supply voltage to overhead 240V mains wiring transformer
On Thu, 03 Sep 2015 13:21:23 +0100, NY wrote:
I'd tend to regard "low voltage" as "definitely capable of being felt but not lethal", and "high voltage" as a voltage that you have some chance of surviving an electric shock from. 240V mains gives you a very nasty belt Not necessarily. I copped a shock from 240V mains a while back and it was no more than a strong tingle. It comes down to the individual's skin resistance and mine (being a bit dry and horny) is a bit higher than most. Would have been a different story with wet hands, though! |
Supply voltage to overhead 240V mains wiring transformer
On Thu, 3 Sep 2015 13:21:23 +0100, NY wrote:
And then apply various levels of "extra high", "super high", "extremely high" adjectives beyond that! 650 V from a third rail would give you very nasty burns and probably kill you. And 25 kV from overhead line train electrification, or 11, 33, 275 or 400 kV from pylon wires, would probably set you alight as well. A 9 V battery has the capability to kill if well enough connected to you. "It's volts that jolts, mils that kills" "mils" being short for milliampere. -- Cheers Dave. |
Supply voltage to overhead 240V mains wiring transformer
On 01/09/2015 16:55, wrote:
On Tuesday, September 1, 2015 at 10:55:02 AM UTC+1, NY wrote: As a matter of interest, what's the typical voltage of the three wires connected to porcelain/glass insulators, mounted on wooden poles, that feed the transformers (often pole-mounted) that step down to 240V for overhead wiring to houses? I can't find anything on Google, using phrases such as "overhead power line 240V" or "low voltage overhead power line". I presume the 240V overhead wiring is 4-wire (ie a star with a wire at each tip and one at the centre) to allow one of the wires to be designated as neutral and thus able to be earthed at each house just before the "electricity board fuse". Does this neutral wire have to be thicker than the other three because it is carrying the return current for all three phases, or do the three return currents usually cancel each other out (at least for the ideal case where all three phase currents are the same magnitude and exactly 120 degrees apart)? It's most likely to be 11kv. It could be 6.6kv 11kv or even very rarely 33v in the UK. It will be delta connected on the primary side. Some rural properties only get two phases on the primary side. Not in the UK, but in some countries abroad the primary side can be a single phase and the return is via the earth. On the secondary there are multiple configurations. It will be star connected. Earth may or may not be combined with neutral on a single conductor or not supplied at all. There may be a single phase, two phases or three phases. Some remote locations have a split phase arrangement on the secondary where the supply is a single phase centre grounded. This allows a supply a little bit more remote from a single phase supplied transformer. The neutral will be earthed at the substation. A combined earth and neutral conductor should be earthed at multiple points along the route. If the load were balanced completely there will be no current on the neutral conductor. In practice there will be current on the neutral conductor but it should not exceed the current on a single phase - it would take a very odd inductive load to do that. Don't use this info for anything other than entertainment. I may be talking out of my arse. Philip The 11kV/240v transformer supplying my house has a 2 wire supply on the 11kV side of it, this is teed off a 3 wire 11kV line a few poles away. --- news://freenews.netfront.net/ - complaints: --- |
Supply voltage to overhead 240V mains wiring transformer
On 02/09/2015 14:39, Dave Liquorice wrote:
On Tue, 01 Sep 2015 22:08:45 GMT, Johnny B Good wrote: It is my understanding that the neutral connection on the LV secondary will be independently connected to a local earthing spike or spikes provided by the utility company responsible for the supply. It may not be as good a low earth resistance connection as that provided in urban substations but it'll be a damn sight safer than relying on an 11 or 6 KV distribution neutral connection (assuming such a connection is provided or even needed in the higher voltage levels of the distribution network). If you ever wander out in the thr countryside and look at the 11 kV power distribution it's all three wire, just the three phases. With a signle phase transformer one side will be connected to a real earth connection at the pole, in our case it looks like a bit of 25 mm^2 before it disappears behind the protective capping and under ground. This earth may or may not be carried on a seperate wire into the house, around here the pole to house connection is mainly just two wire, phase and neutral earth combined. I'm now going to hit send and take a look at what the 'experts' have said and see how big a fool I may have made of myself. :-) The only glaring error is the use of LV to differentiate 240 from 11 kV. To the DNO's 11 kV is "LV", I think 33 kV might be be lowest "HV" but it could be 125 kV. When i worked in the ESI voltages were calssified approximately thus; 1000v LV 1000-35kV MV 35-230kV HV 230kV EHV --- news://freenews.netfront.net/ - complaints: --- |
Supply voltage to overhead 240V mains wiring transformer
"Dave Liquorice" wrote in message
ll.co.uk... On Thu, 3 Sep 2015 13:21:23 +0100, NY wrote: And then apply various levels of "extra high", "super high", "extremely high" adjectives beyond that! 650 V from a third rail would give you very nasty burns and probably kill you. And 25 kV from overhead line train electrification, or 11, 33, 275 or 400 kV from pylon wires, would probably set you alight as well. A 9 V battery has the capability to kill if well enough connected to you. "It's volts that jolts, mils that kills" "mils" being short for milliampere. I imagine that to be "well enough connected" it needs to be via open wounds that penetrate the epidermis and maybe even dermis, and get right to muscle. I wonder what voltage is used by internal paddle-defibrillators and other "jump start" devices for restarting the heart in open-chest heart operations. Probably not much compared with those that are applied to the outside of the chest. Apparently I had many Joules of the latter (as well as many mls of adrenaline and many many chest compressions) when I suffered a heart attack and cardiac arrest four years ago. I have no memory of it! But it did some good because I'm still here and, despite my heart having no pulse for about 90 mins and CPR being the only "pulse" that my body had until A&E got me going again, I suffered no (discernable) brain damage - but then would they be able to tell? :-) A woman I was at university with was able to "feel" voltages as low as a couple of volts with her fingers and was much in demand for her laying-on-of-hands technique in the lab for feeling circuit boards to tell which tracks were live, as an alternative to using a voltmeter! |
Supply voltage to overhead 240V mains wiring transformer
In article ,
"ARW" writes: wrote in message ... If the load were balanced completely there will be no current on the neutral conductor. In practice there will be current on the neutral conductor but it should not exceed the current on a single phase - it would take a very odd inductive load to do that. Like a long row of HID streetlamps running along a motorway. (3rd harmonic adds in 3-phase neutral, rather than canceling out.) Like pikeys pinching a bit of copper that they think is an earth when it is a neutral on a three phase supply. Some years back, a kid got into a substation at the end of a 275kV overhead line, and thought it would be OK to unbolt the earth wires coupling the last pylon to ground. It seems that as the last one was unbolted, the pylon floated up to many kV above earth, and fried him. So real earth wires are not safe to disconnect either. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
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