Practicality of 400 volt equipment

[Cookie]

Would it be practical, or technically possible to economically mass produce 400 volt single phase consumer goods? Light bulbs, kettles, heaters, chargers, TVs, hobs, vacuum cleaners, washers, dryers, microwaves, tools, ect ect?

I'm thinking this would save a lot of copper and make wiring both easier and safer. A 1mm2 cable on a 10 amp breaker would give 4,000 watts of power.

 

[Julie.]

What investigation is there of 400 volts?

Write to the iet or iec and ask them.

 

[Lucien Nunes]

The gist of the OP's question is why not make the default single-phase voltage, i.e the lowest voltage available on the system, 400V rather than 230, regardless of the phase arrangement. So discount whether it's Y or delta, single or three phase, and just consider whether 400V light bulbs, hairdryers, phone chargers etc. are sensible and practical and worth the saving in copper.

The answer I suspect is no.

Historically, the choice of voltage was significantly dictated by both carbon-arc and filament lamp design and 120 years ago, both worked better at 120V than 240. Metal filament lamps are stronger, last longer and are more efficient at lower voltages (hence 12V halogens etc.) In the UK, we actually preferred 120V lamps in series pairs for certain stage lighting purposes instead of 240V and projector lamps were 120V fed from a transformer, because 230V lamps were so fragile and inefficient. We got good at making 230V general purpose lamps but 400V was basically unachievable, so there never was a 400V incandescent lighting option. None of that really applies in 2020.

The fragility argument also goes for many wound components, a small 400V transformer primary or relay coil is more expensive to make and more prone to failure than a 230V one, due to having many turns of very fine wire. Even 230V can be a problem - many small mechanical timeswitch motors (e.g. the defrost timer in the freezer and plug-in timers) actually used a 120V or lower voltage motor, fed by a capacitor dropper, because a 230V type would be too expensive and fragile. 400V would be much more of a problem still.

Discharge lamps with ballasts dictate their own voltage and the ballast takes up the difference between that and the supply. So a metal halide lamp running on 400V will take the same current as one on 230V, just at a lower power factor as the (more expensive) ballast has to drop an extra 170V. Only a transformer would solve this.

But, the main event is the switched-mode power supply, where the electronics on the primary side have to operate at the peak voltage of the supply. In most electronic devices, and any appliances containing electronics, the incoming 230V AC is rectified and smoothed to 320V DC, whereas on 400V the DC rail would be 560V. This requires both smoothing capacitors and chopper transistors of a different tier of performance, which certainly with the components available today would significantly impact the price. 560V is definitely at the top end of what electrolytic capacitors are capable of, and at this voltage it is not uncommon to have to use series pairs with balancing resistors. Possible, but probably not economic, given that many such power supplies use so little power that they would not contribute to any realistic saving in copper. Really small loads that use capacitor droppers, like the ballasted discharge lamps, would simply have to use a more expensive capacitor and drop more volts, with no saving in current.

Therefore I think with the state of the art, small power and lighting is still best served in the 120-230V range, with advantages to both voltages but increasingly in favour of 230V now that filament lamps are not a driving factor.

 

[Simon47]

Given that the idea of switching to 400V delivered as 2 legs of a 3P system, I'm surprised there's been no discussion about how the change coukd be made. It makes me think of the old joke about the tourist asking a local how to get somewhere - only to be told "I wouldn't srart from here".
With the change, single phase systems would now have two line conductors - so you now need 2 pole protection and switching for everything. So you're no needing a partial rewire of every property. Lights looped at the rose now need altering to take the second line down to the switch & back - physically you may be looping at the rose, but electrically the same as looping at the switch and needing a partial rewire. And of course, you'll need to replace most of your accessories to make everything 2 pole switched. And all your plugs will need replacing for ones with 2 fuses - I remember they had some of those at school for the 110V stuff run from 55-0-55V supplies.
So we've replaced all the CUs, partially rewired, replaced most of our accessories and pkugs and ... we still haven't addressed appliances.
So we also persuade everyone to replace their fully servicable appliances for new ones designed for the higher voltage. And they will be new ones as no supply of second hand ones. The day someone suggests that to me, they will learn some "interesting" vocabulary - unless they are offering to pay for it all.

Of course, there is the alternative of adding a stwp down isolating transformer between the meter and CU - at a cost, and if there's room in the modern shoeboxes.

And what do we gain ? Absolutely nothing at all until EVERY custoner on part of the network has been converted.

Conversely, any custoner is free to ignore the DNO provided earth and make their own arrangements - limited only by their access to sonewhere for a suitably earth electrode (system).

Lastly, who here has has the experience of connecting a 110V item to 240V ? Occasionally it's forgetting to check the position of the voltage selector switch. Once in my case it's been someone sending me the wrong (single voltage) part. But generally the results "aren't pretty".
So I would forsee a lot of blown up kit as people plug their 240V items into 400V supplies. Now they wouldn't ? I can assure you that a lot if oeople would - they have no idea what voltage is.
I recall at a previous place, the ladies in the retail shop asked the maintenance guy for some wire cutters. Why ? To cut off the plug and fit a new one on the christmas tree lights - it never occurred to then that the reason for an "odd" plug could be that the lights weren't 240V.

So, woukd 400V be a good idea ?
Possibly - but only if you don't start from here!

 

[Cookie]

You would not need 2 pole switching except at the consumer unit.

 

[James]

You would not need 2 pole switching except at the consumer unit.

For functionality you are correct, for safety I would disagree.

 

[Lucien Nunes]

It doesn't have to be two legs of a 400/230V system. One night, the DNO could uplift your local 400/230V transformer and drop a 690/400 in its place, and presto! 400V Uo in your house.

Switchovers from one voltage or frequency to another and DC to AC have all been done before. When the National Grid drove a rollout of standardised voltage and frequency, electricity suppliers would take your appliances and either modify them for the new supply or replace it if not possible, just as gas appliances were converted from town gas to natural gas. In the museum we have appliances originally made for non-standard voltages that have been reworked and the new voltage engraved onto the plate. E.g. a Hoover vacuum cleaner made for 210V that had a replacement armature fitted and '240V' stamped over the 210. Until recently, a church with a 1920s organ blower wound for 200V was running it from 400 via a transformer supplied and fitted in the 1940s at the electricity supplier's cost. Sites with large inventories of DC plant used to install rectifiers to keep it all running when the mains were converted to AC.

The greater number of appliances in use today and the impracticality of converting most of them makes a repeat of that exercise near impossible, though.

 

[Cookie]

For functionality you are correct, for safety I would disagree.

What safety comes from using a wall switch as a disconnecting means?

 

[Cookie]

It doesn't have to be two legs of a 400/230V system. One night, the DNO could uplift your local 400/230V transformer and drop a 690/400 in its place, and presto! 400V Uo in your house.

Switchovers from one voltage or frequency to another and DC to AC have all been done before. When the National Grid drove a rollout of standardised voltage and frequency, electricity suppliers would take your appliances and either modify them for the new supply or replace it if not possible, just as gas appliances were converted from town gas to natural gas. In the museum we have appliances originally made for non-standard voltages that have been reworked and the new voltage engraved onto the plate. E.g. a Hoover vacuum cleaner made for 210V that had a replacement armature fitted and '240V' stamped over the 210. Until recently, a church with a 1920s organ blower wound for 200V was running it from 400 via a transformer supplied and fitted in the 1940s at the electricity supplier's cost. Sites with large inventories of DC plant used to install rectifiers to keep it all running when the mains were converted to AC.

The greater number of appliances in use today and the impracticality of converting most of them makes a repeat of that exercise near impossible, though.

What was the highest single phase voltage ever used in the UK or anywhere in the world?

 

[James]

What safety comes from using a wall switch as a disconnecting means?

It is often, although not always that an isolator next to an appliance is not only a functional switch but also an isolator.
An oven or a shower would be a couple of things that spring to mind.
It would be unexpected for part of the appliance to remain live after you had switched it off

 

[Simon47]

It doesn't have to be two legs of a 400/230V system. One night, the DNO could uplift your local 400/230V transformer and drop a 690/400 in its place, and presto! 400V Uo in your house.

But in the context that started this off, getting rid of combined neutral & earth, doing that wouldn't really help.

Switchovers from one voltage or frequency to another and DC to AC have all been done before.

Indeed, but back then there weren't huge numbers of appliances - and what there were would have been "properly built". As you point out ...

The greater number of appliances in use today and the impracticality of converting most of them makes a repeat of that exercise near impossible, though.

Indeed. Though I'd have gone further than "near impossible" ! I couldn't see it being done in any other way than lots of transformers. Just a very quick count around the house quickly heads up past 50, before I've included lights and fixed stuff like the boiler. Quite a lot of fixed stuff - PIR detectors, lights, heating controls, pumps, and the list goes on and on.

I think a lot of 25kVA transformers needed ![/QUOTE][/QUOTE]

 

[Cookie]

It is often, although not always that an isolator next to an appliance is not only a functional switch but also an isolator.
An oven or a shower would be a couple of things that spring to mind.
It would be unexpected for part of the appliance to remain live after you had switched it off

Perhaps in the UK but not elsewhere. Keep in mind that close to 50% of the world's population deals with unpolarised schuko plugs on a daily basis.

 

[James]

Perhaps in the UK but not elsewhere. Keep in mind that close to 50% of the world's population deals with unpolarised schuko plugs on a daily basis.

That is different, a plug and socket IS A FORM OF DOUBLE POLE ISOLATION

 

[Lucien Nunes]

I think people conventionally unplug an item if possible, or switch it off if not, before maintenance. The practical result is that with single-pole switching in the line conductor and a solidly grounded neutral, most permanently-installed lighting points are effectively safe to touch (although not isolated) with the switch off. With the increasing use of smart switches, points are more likely to be partially live during relamping and I am not sure that users are generally aware of this.

I was trying to isolate the question of the practicality of 400V appliances from Cookie's previous deliberations on the subject of distributing without a neutral. That might be what inspired this thread but whether a 400V SMPSU is electronically viable is quite a different topic from whether DP light switches are needed for safety. Taken together, then yes there is much to recommend star-grounding the supply to keep Uo at 230V and using two lines.

There is an important advantage of star-connecting single-phase loads to a three-phase system that must be considered. The 3-phase distribution cables, when subjected to diverse and typically balanced load comprising many small single-phase loads, carries little neutral current (except zero-sequence harmonics which are a nuisance whichever way things are wired.) Therefore one gets an implicit transformation, in which the load is taken at 230V but causes only the voltage drop and power loss associated with the same load at 400V. This is true also of the 120/240V split phase system in use in the USA, hence its popularity. Not distributing the neutral does not improve the voltage drop on the 3-phase segment but constrains the user to taking the power at 400V. The efficiency advantage occurs only within the single-phase segment of the wiring.

 

[Cookie]

That is different, a plug and socket IS A FORM OF DOUBLE POLE ISOLATION

Right, when opening up the appliance or tool for service. However beyond that single pole switching is just as safe and gets the job done. You either double insulate or hook an earth wire to the metal. Polarity does not change that.

 

[Cookie]

I think people conventionally unplug an item if possible, or switch it off if not, before maintenance. The practical result is that with single-pole switching in the line conductor and a solidly grounded neutral, most permanently-installed lighting points are effectively safe to touch (although not isolated) with the switch off. With the increasing use of smart switches, points are more likely to be partially live during relamping and I am not sure that users are generally aware of this.

I was trying to isolate the question of the practicality of 400V appliances from Cookie's previous deliberations on the subject of distributing without a neutral. That might be what inspired this thread but whether a 400V SMPSU is electronically viable is quite a different topic from whether DP light switches are needed for safety. Taken together, then yes there is much to recommend star-grounding the supply to keep Uo at 230V and using two lines.

There is an important advantage of star-connecting single-phase loads to a three-phase system that must be considered. The 3-phase distribution cables, when subjected to diverse and typically balanced load comprising many small single-phase loads, carries little neutral current (except zero-sequence harmonics which are a nuisance whichever way things are wired.) Therefore one gets an implicit transformation, in which the load is taken at 230V but causes only the voltage drop and power loss associated with the same load at 400V. This is true also of the 120/240V split phase system in use in the USA, hence its popularity. Not distributing the neutral does not improve the voltage drop on the 3-phase segment but constrains the user to taking the power at 400V. The efficiency advantage occurs only within the single-phase segment of the wiring.

Does the UK implement any forum of over-voltage protection should a neutral break?

Agree, but for the sake of the argument, there are advantages in not distributing a neutral. Many of which become greater with system size, number of sources and the presence of automatic transfer switches.

One must keep in mind there are countries like South America which derive 220 volts Line-Line when they could just as easily have gone 220/380Y.

Two options exist in theory:

1) Design all single phase equipment for 400 volt operation and use 230/400Y trafos.

2) Keep the present standard of 230 volts. Homes and small buildings supplied via 133/230Y trafos. Large buildings supplied via 277/480Y, 347/600Y or 400-415/690-720Y transformers. 690 volts is taken to directly to large motors and equipment while transformers seeded around the building take 690 volts down to 230Y for lighting and socket loads.

I'm left left wondering if the wire savings and efficiency of 690 volts along with lower dielectric requirements of 230 volt equipment outdoes the material cost of transformers, their associated losses and larger cable in smaller supplies.

Of course there is the 3rd option of 230/400Y with the neutral distributed taking into account the complexities of 4 pole isolation and protection against an open neutral.