Post by: evan_au on 21/09/2016 22:32:19
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Why is the mains electricity supply in the UK 240V AC? Why not, for example 400V DC?In the early days of electricity distribution, there was a vicious competition between Edison (promoting DC) and Tesla (promoting AC).
It included underhanded tricks such as Edison secretly sponsoring the development of the electric chair, provided it ran on AC. This was then used to attack the AC camp in the public mind.
In the end, Tesla's AC system won, because:
- it was easier to convert between voltages with a transformer (no moving parts)
- it was easier to transmit voltages a long way with AC (use a higher voltage)
- The copper conductors were cheaper with AC (3 wires carrying AC could carry 3 times the power of 2 wires carrying DC)
...despite the fact that the typical 30-60Hz mains frequency is in the range where human muscles are quite sensitive (airplanes traditionally used 400Hz, which allows much smaller and lighter transformers).
- In the USA, they went for safety (110V AC) - perhaps influenced by Edison's smear campaign?
- In the UK, they preferred efficiency (240V AC) - lower resistive losses
See: https://en.wikipedia.org/wiki/Three-phase_electric_power
Post by: jerrygg38 on 22/09/2016 14:30:32
As I read the daily teletype, people were sometimes getting killed chopping ice from their refrigerators with a knife or ice pick and hitting the wires. Other people merely destroyed their freon in the process. Other people died by picking up series street lighting which could rise to 5000 volts when wires fell down. Thus 120 volt street lights can give you a 5000 volt shock.
In Brooklyn Tech H.S. they had 600 volt DC switches and people put their fingers across the blades. Well stupidly I did it and found no effect. But then I said "Your have to squeeze" and then I did and I got a shock but it was more funny than bad.
Post by: Semaphore on 22/09/2016 15:33:13
When I started working for Con Edison NY in 1956, they still had 120volt DC service. The company wanted to get rid of it and gave away AC fans for free. The shock of DC is easier to handle than AC. 120 volt ac rises to a peak value of 169.7 volts. Having been shocked many times in my life this can hurt us. To go to 240 volts ac will kill us faster. I am surprized to learn they use this in the UK.
As I read the daily teletype, people were sometimes getting killed chopping ice from their refrigerators with a knife or ice pick and hitting the wires. Other people merely destroyed their freon in the process. Other people died by picking up series street lighting which could rise to 5000 volts when wires fell down. Thus 120 volt street lights can give you a 5000 volt shock.
In Brooklyn Tech H.S. they had 600 volt DC switches and people put their fingers across the blades. Well stupidly I did it and found no effect. But then I said "Your have to squeeze" and then I did and I got a shock but it was more funny than bad.
Sounds like some Darwin awards have been handed out. Interesting stories, anyway.
Post by: syhprum on 22/09/2016 20:29:53
Although domestic supply is rated at 120 V many houses have a 2 phase supply giving 240 V for higher power loads
One of the problems with DC supplies is that arcs persist try taking a running lamp out of its socket !
Post by: jerrygg38 on 22/09/2016 22:00:00
The street lights were not 120 V but originally consisted of many arc lamps wired in series that is why such a high voltage was employed.The lights I saw in New York City were quite ordinary incandescent bulbs. They were wired in series but they had a constant current transformer driving them. (An original current source). Open circuit brought the maximum voltage to the point of the open. If a bulb burnt out you could shut down the transformer and temporarily jump the bulb until a replacement has been found.
Although domestic supply is rated at 120 V many houses have a 2 phase supply giving 240 V for higher power loads
One of the problems with DC supplies is that arcs persist try taking a running lamp out of its socket !
The NY subway trains still use DC supplies for the third rail. Another problem with DC system is they help cause electrolysis which damages structures in the environment. NY had technicians and engineers whose only job was to eliminate electrolysis problem. Although I had worked for the Dept. Water Supply Gas and Electricity for 5 years after Con Edison, I was only involved with Street lightning and knew little of the electrolysis problems which also occur naturally.
Post by: syhprum on 22/09/2016 22:57:03
Post by: jerrygg38 on 23/09/2016 00:40:12
One of the reasons for employing a series connection and a constant current supply was because arc lamps have a negative dynamic resistance and must be supplied from a constant current source (as I found out at the age of ten when I shorted out the feed resistor!) probably when filament lamps were installed the original wiring was retained.One other very interesting series circuit that Con Edison employed was a series capacitor circuit so that the power went through a capacitor first and then the copper wiring. This was a high voltage circuit at least 4KV or even higher. Hard to believe they would do such things. Why? The answer is that it was a dedicated line going to a high current spike welding company. Parallel capacitors did not work but the series capacitor did the job. This brings me back to when I started work at 17.5 years and went to college at night.
Post by: Bored chemist on 24/09/2016 12:54:31
I am surprized to learn they use this in the UK.
It's less surprising when you recognise that we generally have more sense than to connect ourselves to the electricity supply which makes the voltage less important. I guess the same is true of our friends in the rest of Europe and also China, India, Australia, New Zealand, much of Africa, and- well essentially everywhere outside the US (and, curiuosly, Japan)
https://en.wikipedia.org/wiki/Mains_electricity_by_country
Also. many homes + businesses in the US also have 240 V supplies.
Post by: alancalverd on 24/09/2016 13:57:41
Quote
I am surprized to learn they use this in the UK.
Alas, no longer! You can still get 240V rms single-phase in Australia, but the UK standard was dropped some years ago to conform to the EU requirement. The rest of Europe uses 220V but cheats:
from Schneider - Electric UK Ltd
Quote
For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage to 240VAC + 6% and - 10% and European to 220VAC +10% and -6% (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!
Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range
If a product is to be used in the UK a 240VAC rated device is ideal but either 240VAC or 230VAC products can be used with confidence.
If a product is to be used in mainland Europe or Irish Republic a 220VAC rated device is ideal but either 220VAC or 230VAC products can be used with confidence.
Problem is that if you use a 240V motor at the minimum permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.
Post by: Bored chemist on 24/09/2016 14:11:22
Problem is that if you use a 240V motor at the minimum permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.
So, let me get this straight-because a machine didn't comply with our national standards (which happen to coincide with EU ones) requiring satisfactory operation across a range of voltages, you suggested to patients that they should vote for the UK to refuse to take part in the specification of the EU standards (which the manufacturers will still have to meet if they want to sell in their biggest market- the EU)
How does refusing to take part in the setting of standards improve them?
Are you saying the the UK's contribution to the EU standards was so stupid that the standards will be better without us?
That seems a rather harsh judgement.
Post by: vhfpmr on 25/09/2016 00:29:34
Problem is that if you use a 240V motor at the minimum permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.
If the MRI has been sold to a customer who doesn't have the correct supply voltage, or a designed with a motor which doesn't run off the same supply as the MRI, that's not the fault of the European specification. If I design radio using 24V power parts, and specify it to run off a 12V supply, I can't blame the supply when the transmitter power output falls short.
Post by: alancalverd on 25/09/2016 16:04:22
The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.
The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.
Post by: syhprum on 25/09/2016 17:04:18
I worked for Perske Price Services that provided large picture processing Systems from Hell GMBH in Kiel, these were always supplied with multi tap 6 KVA transformers to allow for power supply variations.
Post by: William McC on 25/09/2016 17:11:41
QuoteI am surprized to learn they use this in the UK.
Alas, no longer! You can still get 240V rms single-phase in Australia, but the UK standard was dropped some years ago to conform to the EU requirement. The rest of Europe uses 220V but cheats:
from Schneider - Electric UK LtdQuoteFor many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage to 240VAC + 6% and - 10% and European to 220VAC +10% and -6% (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!
Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range
If a product is to be used in the UK a 240VAC rated device is ideal but either 240VAC or 230VAC products can be used with confidence.
If a product is to be used in mainland Europe or Irish Republic a 220VAC rated device is ideal but either 220VAC or 230VAC products can be used with confidence.
Problem is that if you use a 240V motor at the minimum permitted "230V" supply voltage (220V - 6%) it will only deliver 75% of its rated power. This has caused me serious problems trying to cool an MRI machine on the hottest summer days. Patients were turned away and invited to vote for Brexit.
You can install buck boost transformers, which are actually very small and rather inexpensive, especially for three phase systems. An 18kw boost system is actually very small they almost look like low voltage lighting transformers.
Sincerely,
William McCormick
Post by: alancalverd on 25/09/2016 17:46:25
the reason people voted brexit is that they brain washed by the gutter press are so terrified of immigrants that they would rather see our economy ruined.
Neither true in my case. Simply a lot of experience of the idiocy and corruption that goes into EU Directives (I am a registered European Union Expert Consultant in my field), and the fact that the UK has always had a negative balance of trade with continental Europe: more trade = more loss, as shown by official EU statistics.
A descendant of fairly recent immigrants, my concern over recent expansion of the EU has been with the mobility of cheap labor from areas with a very low cost of living. I can hire a medical consultant from Romania for the same salary that I would have to pay a first-year UK graduate. It's a good deal for the breadwinner whose family stays in the east (the difference between a migrant worker and an immigrant), and a good deal for me, but the prospect is that British graduates will become unemployable in the medium term, or unable to live in the UK, and that ain't good. Meanwhile I can't hire Australian nurses at any price because unlike EU citizens, they have no automatic right to work here or have their qualifications recognised.
Post by: William McC on 25/09/2016 18:22:19
Politics is a planed chaos to hide failure and a lack of science. If you can make sense of politics perhaps you are part of the problem.
As an American I can tell you we went down the same twisted path, we are about over as a nation, hypocrisy has almost devoured all that we had, which was the amazing science that Benjamin Franklin unlocked while doing a hundred other good deeds.
Some years ago Germany started producing micro natural gas turbines. Which could be installed in commercial buildings to supply not only all the electric for the building but also heating and cooling using the heat generated by the turbines operation for both heating and coiling.
If you are not aware many cooling systems like the one in the JFK Airport, U.S. post office, fire oil burners to heat and pressurize lithium bromide, the lithium bromide is allowed to pass through a condenser coil where it is cooled, then still under pressure injected into the chiller where it evaporates and absorbs the heat from the building. That was the plan using these German micro turbines. Now is it the best method no, was it better than what we had yes. The U.S. government had promised tax breaks to any company that installed them. Many small businesses that install such equipment geared up and then the government at the very last second pulled the tax breaks and almost all the small high tech companies went out of business or almost out of business overnight.
Germany needs to have the courage to announce the reality and technology that they are currently trying to slip into our day to day lives. Every time they create something and do not accurately describe it or downplay its efficiency, in the long run they are just hurting their credibility. The only way into our markets is with more efficient products, but they do not want that label. Or the responsibility of describing how it works.
Sincerely,
William McCormick
Post by: syhprum on 25/09/2016 19:05:17
Hence a 18KVA transformer needs only a core size appropriate for 2KVA
Post by: Bored chemist on 25/09/2016 20:42:38
The MRI chiller motor was manufactured in Germany to the EU specification. As for manufacturing MRI in the UK, we haven't done so since 1985.
The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.
The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.
"The MRI chiller motor was manufactured in Germany to the EU specification."
So, either it was built to run on 230V as in Germany, or it was built to the EU standard in which case it would have run properly on the bottom end of the EU range.
Or, it just wasn't up to the job- It's not clear how leaving the EU would stop German manufacturers making duff motors.
Could you expand on that for us?
This "As for manufacturing MRI in the UK, we haven't done so since 1985. "
only matters if the only business in the EU is the manufacture of MRI machines.
Whenn everyone has finished grumbling about power limits they don't really understand, we will be using less energy to vacuum our carpets (and saving money in the process)
It's a counterpoint to the daft state of affairs where cleaner manufacturers were playing the same silly "numbers game" that PC makers did with clock rates a decade or so back.
The energy used by a cleaner is the product of the power and the time taken. A 10KW vacuum cleaner doesn't mean you can walk round the room in a 20th of the time it takes to walk round with a 500W one
Meanwhile, on the morning of the Brexit the UK lost a lot of money- something like the value of the Greek economy.
Also, that morning, their main spokesman Mr Farrage, admitted that he had lied about the biggest factor they were able to put in favour of leaving (The lie about funding the NHS).
However I'm still waiting for an explanation of how us leaving the EU will improve the regulations (It seem that both you and I were involved in the rules- you implement them and I was involved in drafting them)
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.
Now they won't have any representation on the drafting of those rules.
How is that better?
Post by: William McC on 25/09/2016 21:21:55
The MRI chiller motor was manufactured in Germany to the EU specification. As for manufacturing MRI in the UK, we haven't done so since 1985.
The UK was, of course, and still is, a member of the union that limited the consumption of domestic vacuum cleaners to 1600W, allegedly "to save energy". Fact is that the newest members of the Union have domestic mains limited to 7 amp sockets, so in order to give their manufacturers access to a genuine single market, the market had to be restricted to 7 A x 230V = 1610W. Politics, not physics, rules the EU.
The giveaway is the proposed limit on hairdryers, kettles and lawnmowers to - you guessed it, 1600W. The official reason is half honest: reduced power (not energy!) consumption and fewer imports into the EU. It's bloody obvious that when it comes to heating or evaporating water, the energy requirement has little or nothing to do with power consumption: indeed a low power kettle will require slightly more energy to heat through a given temperature range because the surface loss rate at any given temperature is the same.
"The MRI chiller motor was manufactured in Germany to the EU specification."
So, either it was built to run on 230V as in Germany, or it was built to the EU standard in which case it would have run properly on the bottom end of the EU range.
Or, it just wasn't up to the job- It's not clear how leaving the EU would stop German manufacturers making duff motors.
Could you expand on that for us?
This "As for manufacturing MRI in the UK, we haven't done so since 1985. "
only matters if the only business in the EU is the manufacture of MRI machines.
Whenn everyone has finished grumbling about power limits they don't really understand, we will be using less energy to vacuum our carpets (and saving money in the process)
It's a counterpoint to the daft state of affairs where cleaner manufacturers were playing the same silly "numbers game" that PC makers did with clock rates a decade or so back.
The energy used by a cleaner is the product of the power and the time taken. A 10KW vacuum cleaner doesn't mean you can walk round the room in a 20th of the time it takes to walk round with a 500W one
Meanwhile, on the morning of the Brexit the UK lost a lot of money- something like the value of the Greek economy.
Also, that morning, their main spokesman Mr Farrage, admitted that he had lied about the biggest factor they were able to put in favour of leaving (The lie about funding the NHS).
However I'm still waiting for an explanation of how us leaving the EU will improve the regulations (It seem that both you and I were involved in the rules- you implement them and I was involved in drafting them)
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.
Now they won't have any representation on the drafting of those rules.
How is that better?
The problem is that 208 voltage motors run nicely up to 220 volts. Which is what you get from 208 volt supplies. 208 volt motors will run on higher voltage but sometimes you start to get that angry hum out of them just above 230. And at night you can get that very angry hum.
The truth is that if you examine the wave forms they are no longer what we paid for. So they raise and lower voltage specific to areas to compensate for large equipment starting up.
At nighttime in industrial parks 540 volts or more from 480 volt systems that used to be 460 volt systems, and before that 440 is not uncommon.
I think it is mostly due to unbalanced three phase loads.
Our electrical voltage test meters started out reading voltage higher and higher from the electric company, so they introduced RMS meters, then the RMS meters started reading voltage higher than what we were supposed to read. So they introduced true RMS meters. I do not know what is coming next because I can often read 253 volts from company supplied 240 volt AC current from a true RMS Fluke meter. The voltage from the duplex outlets in the store were reading 125 volts. The owner made a call and suddenly we had 118 volts at the same time of night.
Sincerely,
William McCormick
Post by: alancalverd on 25/09/2016 23:02:42
Quote
There's no way round the fact that UK manufacturing industry will still have to stick to the EU regs for much- probably most- of their market.What manufacturing industry?
From the Office for National Statistics
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In the 3 months to April 2016, the UK’s trade in goods deficit with the EU widened by £0.6 billion, to a record 3 monthly deficit of £23.8 billion. In the 3 months to April 2016, exports of goods to the EU increased by £2.1 billion and imports of goods from the EU increased by £2.7 billion, to a record 3 monthly level of £58.6 billion.
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Now they won't have any representation on the drafting of those rules.Puts us on a par with China and India, who export all sorts of stuff to the EU. Fact is that if your product meets the CE specification, it can be placed on the market in any of 28 countries without having to meet individual national specifications. And since the CE specification is generally the same as the ISO specification, you'd have to meet it anyway to sell to the USA.
Quote
How is that better?We won't have to pay for the privilege of being outvoted and told what to do.
Post by: syhprum on 26/09/2016 14:54:20
This would seem to be a much less drastic response than what you had suggested.
it is my experience with the Germans that they consider all non German speaking countries as primitive and third world so if have any telephone discussion of this problem it would be best to find a native German speaker to assist.
Post by: William McC on 27/09/2016 01:07:48
If it is a package unit with multiple compressors and they share a condenser cooling air discharge both compressors should be running for any testing.
The new Field Piece HVAC gauges are pretty cool and have temperature sensors built it. But you can do a sub-cooling with regular old fashioned gauges and a thermocouple attached to a multi-meter. Sometimes I cheat and use the infrared temperature sensor.
It is remarkable how the amperage goes way up on very hot days. One other trick that is pretty cool is installing a small bypass damper, a barometric damper. This allows your evaporator to run a bit cooler which also lowers your amperage substantially. It will also cause the output air from the evaporator to be a bit cooler. As long as you do not freeze over your evaporator it is a very efficient thing to do. It only cuts down the CFM a little bit. It is less efficient technically, however it is often much more practical and useful.
If you are running a rack system with hermitic or semi hermitic compressors, with a chiller, condenser, and chilled water piped to your air handler, you can check the cooling tower water flow to the condensers, and the water output temperatures, lack of enough cooling tower water flow will cause high head pressure and higher RLA. If you are getting air output that is not cool enough from your air hander, you might try lowering the fan speed in the air handler, that circulates the room air. This can sometimes be accomplished by a pulley change, or by other controls. That will definitely lower your RLA.
Sincerely,
William McCormick
Post by: Bored chemist on 31/05/2022 19:07:24
The energy used by a cleaner is the product of the power and the time taken. A 10KW vacuum cleaner doesn't mean you can walk round the room in a 20th of the time it takes to walk round with a 500W one
It took a while
https://newsthump.com/2017/03/29/dyson-begins-work-on-new-10000-watt-vacuum-cleaner-for-proud-brexiters/?fbclid=IwAR3IS7AfhZeoPK5uAKBj-tNtsl-FLeeGxXcNXLv3fb-bJVT_BIPOU-6S9_M
Post by: SeanB on 02/06/2022 16:52:07
Series strings won out because they save on expensive copper wire, as you needed to have an extra conductor to carry the current, and with only 1 wire on the original light circuit you saved a lot of money, as you could either run the wire in a loop, cut in where needed to put a lamp, and still have them work, or you could simply put a ground mat at the far ens and use ground return for the one wire. One thin wire rated for a single lamp current of around 2A, and cheap ceramic insulators for 10kV on the supply side, and in the lamp units, to pass this through. Only later on, when they started to have houses supplied on the same poles, did the lighting manufacturers remove the constant current transformers and go to parallel lamps fed off a thicker wire that carried the lighting current. Constant current also was used with discharge lamps, which is why the lamp powers were odd things like 325W and 125W, because at those currents the lamp would operate like the original carbon rod, but with longer life and higher light output. No ballast required, just screw the new lamp into the exact same incandescent E40 socket, and same paper cutout, for triple the light output and 20 year life.
The killer for the series circuit was energy efficiency, you could have up to 60% of the input power as heat in the constant current transformer, but they are still used as airport approach lights, simply because they make monitoring for failed lamps easy, and a broken cable is easy to detect automatically. However even here they are rapidly being replaced by LED, as the lower running cost is a big factor, and you can integrate monitoring into the LED units as well, though you need to replace all cabling with new.
Street lighting also went more to local photocells, so as to limit the step load of turning on all of a city lights all at once, instead the load slowly ramps up over a half hour or so as the sun sets, easy to follow with power plant output. As well going to LED drops power use, your 400W HPS/MH/MV or 60W SOX main road light now is 135W to 220W, a saving in power, and side street lighting went from 125W/80W MV/MH/HPS or 36W SOX (mostly the UK only, with the monochromatic red sodium light of low pressure sodium) being replaced with 36W LED fixtures.
But as to voltage, it is all fixed by the original inventors, and the insulation they had determining the voltage at which it would not break down. 120VDC for the first Edison generators, as the rotors would break down at higher voltage, with the shellac and cotton insulation they had. This then got fixed in stone, as subsequent systems had to be compatible with the old system, and the UK and rest were later, with improved insulation that allowed over 200VDC output, and 240VDC by simply using improved insulation. UK originally used mercury arc rectifiers, so had 2 240VDC lines in the street, with one half of the street getting positive with respect to the grounded common, and the other half negative. For resistive loads not a worry, but the new fangled radiograms needed to be set to which side of the street you were, and later on needed to have a rectifier tube put in for AC use. By the time TV came into use AC mains was the norm, only a very few small areas were still DC ,and they got changed out rapidly.
As an anecdote, across the road is an old tramway substation, where there is still the old mercury arc rectifier room, separate from the transformer control gear hall, and one empty bay where the one transformer was. Mostly empty, all gear long gone, except for the bolts left in the walls, and the cut off remains on the floor. Cables are still in the ground, never removed, there was still the one DC feed head till 2009 outside.
Post by: Petrochemicals on 06/06/2022 07:57:59
Post by: evan_au on 06/06/2022 11:03:57
Quote from: Petrochemicals
Huh...246VThe video doesn't play for me, but are you asking why the voltage reads 246VAC instead of 240VAC?
The mains voltage is not perfectly regulated, but can vary up and down by ±10% (although +20% might shorten the lifetime of some old-fashioned incandescent lamps).
- In particular, if there are a lot of solar panels in your street, the voltage can increase during the day.
- The power transformers in the street were designed for delivering power from a centralized power sation to distributed consumers. The turns ratio in the transformer is not ideal for delivery of distributed solar power back into the central grid.
- Solar panels are designed to reduce their power output when mains voltage gets too high in the street
Another factor that can affect the reading on a multimeter is if the voltage is not sinusoidal - for example if it has significant harmonics.
Post by: Petrochemicals on 07/06/2022 06:19:25
No its an American showing you that 2 phases ammount to 246v I believeQuote from: PetrochemicalsHuh...246VThe video doesn't play for me, but are you asking why the voltage reads 246VAC instead of 240VAC?
The mains voltage is not perfectly regulated, but can vary up and down by ±10% (although +20% might shorten the lifetime of some old-fashioned incandescent lamps).
- In particular, if there are a lot of solar panels in your street, the voltage can increase during the day.
- The power transformers in the street were designed for delivering power from a centralized power sation to distributed consumers. The turns ratio in the transformer is not ideal for delivery of distributed solar power back into the central grid.
- Solar panels are designed to reduce their power output when mains voltage gets too high in the street
Another factor that can affect the reading on a multimeter is if the voltage is not sinusoidal - for example if it has significant harmonics.
Post by: alancalverd on 07/06/2022 09:16:57
Post by: Bored chemist on 07/06/2022 13:13:30
Post by: alancalverd on 07/06/2022 16:44:37
Post by: Bored chemist on 07/06/2022 18:15:35
They are usually accurate to +/- 1 digit......When they leave the factory
The basic voltmeter chip is a DC instrument so for AC you add a bridge rectifier and a 1.41:1 voltage divider to give an estimate of the rms voltage, assuming the waveform is sinusoidal and the rectifier forward voltage is negligible.I think you forgot something.
Post by: vhfpmr on 07/06/2022 18:25:08
They are usually accurate to +/- 1 digit, but don't necessarily display what you are expecting for the reason given above. The basic voltmeter chip is a DC instrument so for AC you add a bridge rectifier and a 1.41:1 voltage divider to give an estimate of the rms voltage, assuming the waveform is sinusoidal and the rectifier forward voltage is negligible.Digital multimeters use dual-slope integration (https://www.eeeguide.com/dual-slope-integrating-type-dvm/) ADCs because the integration smooths noise and ripple, and because the integration period can be made a multiple of 10ms for further rejection of mains related hum. They are also independent of integrator time constant and the clock frequency. Like moving coil analogue meters, DMMs (that aren't true RMS) are sensing the DC average of the input, which for a rectified sine wave is 0.637, and the form factor is therefore .7071/0.637 = 1.11. To measure RMS values of waveforms other than a sinusoid, you need to divide by 1.11, and then multiply by the form factor for the waveform in question.
True RMS meters are only really helpful if you don't know the waveform, and have a resistive load. In the common case when you have a load running from a rectifier and capacitor input filter you have neither, and a more accurate estimate of power can be had by multiplying the peak voltage by the mean current if you don't have a power meter.
±1 digit on a 3½ digit DMM would be an accuracy of ±0.05%, which is tall order even for a good quality instrument like a Fluke. The 1 digit on digital instruments is in addition to the basic accuracy, of 1%, or whatever.
Post by: Bored chemist on 07/06/2022 18:37:28
If you put a bridge rectifier and a capacitor in the circuit you can measure (pretty nearly) the peak voltage and that is 1.141 times the RMS value (if you have a sinewave).
Oops!
Typo
1.414 times the RMS value (if you have a sinewave).
Post by: vhfpmr on 17/06/2022 16:55:41
Alan nearly got the right answer.No, non True-RMS meters are mean sensing, not peak-sensing, and this is usually stated explicitly on good quality meters.
If you put a bridge rectifier and a capacitor in the circuit you can measure (pretty nearly) the peak voltage
Putting smoothing capacitors in meters would make them susceptible to large errors caused by noise spikes.
https://en.wikipedia.org/wiki/Form_factor_(electronics)
Quote
and that is 1.141 times the RMS value (if you have a sinewave).1.414
Post by: Bored chemist on 17/06/2022 17:55:20
No, non True-RMS meters are mean sensing, not peak-sensing, and this is usually stated explicitly on good quality meters.
The easy way to get an average is still to use a capacitor. (or the mass of the needle in an analogue meter)
The value you use (and that of the shunt resistor) is dependent on the frequency range- which can make things awkward.
Post by: alancalverd on 17/06/2022 18:21:13
No, non True-RMS meters are mean sensing, not peak-sensing, and this is usually stated explicitly on good quality meters.The average value of a full-wave rectified sine is 0.637 Vpeak, which is not easy to sense or sensible to display.
Post by: vhfpmr on 19/06/2022 17:37:09
Yes, I know:No, non True-RMS meters are mean sensing, not peak-sensing, and this is usually stated explicitly on good quality meters.The average value of a full-wave rectified sine is 0.637 Vpeak
Like moving coil analogue meters, DMMs (that aren't true RMS) are sensing the DC average of the input, which for a rectified sine wave is 0.637, and the form factor is therefore .7071/0.637 = 1.11. To measure RMS values of waveforms other than a sinusoid, you need to divide by 1.11, and then multiply by the form factor for the waveform in question.
which is not easy to sense or sensible to display.It's trivially easy to sense, you just leave the smoothing capacitor off the rectifier, and meters don't display mean level, they are calibrated in terms of RMS.
"Mean Sensing, Calibrated RMS":
TM3B.png (680.75 kB . 883x402 - viewed 1936 times)A capacitor directly on the output of a rectifier will give you peak, or something close to it, because the rectifier charges it but doesn't discharge it. That's what rectifiers do, only conduct in one direction.No, non True-RMS meters are mean sensing, not peak-sensing, and this is usually stated explicitly on good quality meters.
The easy way to get an average is still to use a capacitor. (or the mass of the needle in an analogue meter)
The value you use (and that of the shunt resistor) is dependent on the frequency range- which can make things awkward.
Smoothing at 0, 40ms, & 120ms:
rect.png (23.57 kB . 1150x514 - viewed 2038 times)Post by: Bored chemist on 19/06/2022 19:42:17
A capacitor directly on the output of a rectifier will give you peak, or something close to it, because the rectifier charges it but doesn't discharge it. That's what rectifiers do, only conduct in one direction.Thank you for restating my point.
In that graph of yours the voltage drops between each peak.
Why is that?
Is it because of current flowing into the meter?
Would that be dependent on the effective resistance of the meter shunting the capacitor?
Would the extent of the "droop" depend on the frequency of the supply as well as on the effective resistance and the capacitance?
Have you also just shown more or less what I said here?
The value you use (and that of the shunt resistor) is dependent on the frequency range- which can make things awkward.
Post by: vhfpmr on 28/06/2022 17:23:30
The easy way to get an average is still to use a capacitorIf you want an average reading instrument you need to leave the capacitor off. Put a capacitor on the output of a rectifier, and you'll have a (close to) peak reading instrument, because the charge and discharge currents are dissimilar, as shown in the plot above. If you need to smooth the ripple with a capacitor and still retain the mean sensing, you need a buffer between the rectifier and the smoothing.
Post by: Bored chemist on 28/06/2022 17:46:51
If you are using a digital meter then you need to so something more complicated to get rid of aliasing errors.
The easiest way to do that is with a capacitor or some such to roll off the high frequencies.
Post by: SeanB on 29/06/2022 18:35:44
Post by: Bored chemist on 29/06/2022 18:46:11
Digital meters use integration, selecting the time constants of the integration so that it is a multiple of both 50 and 60Hz mains,Other frequencies are available.
You might also try one of these- a pretty good RMS measure independent of crest factor and frequency over a very large range.
https://en.wikipedia.org/wiki/Ammeter#Hot-wire
Post by: SeanB on 30/06/2022 06:06:41
Other frequencies are available.Yes, but not at all common these days, mostly reserved for RF measurements. Fluke and Agilent offered the meters, but both companies no longer can supply the delicate balanced thermal measuring unit that is at the heart of them any more. They lost the technical ability to make them.
You might also try one of these- a pretty good RMS measure independent of crest factor and frequency over a very large range.
https://en.wikipedia.org/wiki/Ammeter#Hot-wire
The nice thing about choosing to be compatible with 50/60Hz as integration frequency is that you also get good repeatability with the other common supply frequency of 400Hz, and almost all meters that are calibrated for 50 or 60Hz will have similar accuracy at 400Hz, though you can also get them certified for this, along with up to 20kHz if desired. Yes most common DMM chipsets will work up to 100kHz no problem, though some will exceed that by a large margin, often up to 100MHz on some, with reduced accuracy. Really depends on how it is laid out and what care you take with using the reference design.
Post by: paul cotter on 30/06/2022 13:26:24
Post by: JesWade21 on 16/08/2022 12:49:49
Post by: evan_au on 17/08/2022 00:09:16
Quote from:
DC connections can be found everywhere, including every major interconnect.This applies specifically at interconnects between:
- Different frequency networks: One side of Japan is 50Hz, the other is 60Hz. So when the east-coast earthquake knocked out power stations, they had limited capacity to buy electricity from the west coast through DC interconnects.
- Different phase networks: Texas runs at nominally 60Hz (same as the rest of the USA), but is not phase-locked to the rest of the USA. So when a cold snap froze gas plants in Texas, there was limited ability to buy electricity from the rest of the USA through DC interconnects.
- In phase-locked grids, the cheapest interconnects are AC, powered by 3-phase transformers
- But, driven by the revolution in high band-gap semiconductors, the price of AC-DC and DC-AC conversion is dropping rapidly. This provides other advantages, like long-distance transmission lines with no power factor, and software-controlled power-factor compensation.
Post by: JesWade21 on 22/08/2022 11:25:01
Post by: Bored chemist on 22/08/2022 12:46:14
Because it's a dozen score.
Post by: paul cotter on 22/08/2022 16:43:48