Discuss Practicality of 400 volt equipment in the Electrical Forum area at ElectriciansForums.net

Aico 3000
Wetroom Store - Network Wetroom Suppliers
This official sponsor may provide discounts for members
C

Cookie

-
  • Thread Starter Thread Starter
  • #38
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 In the museum we have appliances originally made for non-standard voltages that have been reworked and the new voltage engraved onto the plate.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

James

-
Mentor
Esteemed
Arms
Supporter
Patron
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
 
S

Simon47

-
Esteemed
Arms
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]
 
C

Cookie

-
  • Thread Starter Thread Starter
  • #41
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

James

-
Mentor
Esteemed
Arms
Supporter
Patron
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

Lucien Nunes

-
Mentor
Esteemed
Arms
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.
 
C

Cookie

-
  • Thread Starter Thread Starter
  • #44
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.
 
C

Cookie

-
  • Thread Starter Thread Starter
  • #45
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.
 
S

Simon47

-
Esteemed
Arms
Keep in mind that close to 50% of the world's population deals with unpolarised schuko plugs on a daily basis.
Do you have any feel for how many (what proportion) of appliances aimed at such markets use 2 pole switching internally ? I've only a limited sample, but a significant proportion of those I've ever had to look inside (especially things like drills and other hand-held tools) have had double pole switching. But as mentioned, it should be routine to pull the plug before opening anything up or poking things in - as a farmer I once worked for did, start clearing the air vents on an angle grinder with a metal pocket knife (he did quickly unplug it when I pointed out it was still plugged in).
Does the UK implement any forum of over-voltage protection should a neutral break?
Generally not - as attested to by news reports of household fires when some scrote nicks £20 of neutral link from the substation.
But it's not just the phase-neutral voltage that's an issue - and that could be dealt with by a voltage monitoring relay to disconnect the supply. There's an electrical safety issue in having the MET, and hence everything attached to it, at a potential that's very different to local earth. Not too bad inside where there's equipotential bonding, but bad news for someone leaning on their car and touching a metal bollard/lamp post/whatever nearby (and hence the extra requirements for charging points).
I was under the impression that the idea sparking off the original question was along the lines of "if people switched to 400V for single phase, we (or more correctly, the DNOs) could ditch the neutral and use the current combined N&E as an earth only for a TN-S supply".
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.
I worked very very briefly aboard a ship that used the same system - 3 wire 3 phase, 220V phase-phase and everything connected across 2 phases. Well to be more accurate, some things were like that, most of the ship was still 220V DC - they'd converted one generator to AC to allow all those AC appliances people like to have to work, while most large loads were still DC. I noted while doing a little electrical job in the engine room, that there was an air compressor driven by a motor with a higher power rating than my car engine !
Fortunately for them, all the circuit breakers (which must have been exceedingly modern for something built in the early 50s) were AC or DC so they only had to add a third wire to the main distribution boards and distribute the sub mains to the local boards across the 3 wires. So getting single phase AC to the hotel loads was fairly easy. The breakers were also 2 pole - I think all the system was floating and nominally +/-120V. I know the emergency lighting was as they had a pair of indicator lights by the battery tank to indicate if there was an earth fault - both lights dim and equal = nothing dragging one side of the DC to the hull.
And everything was originally labelled in Italian. And on push button starters, the red button was for start and the green button for stop - which seems much more sensible to me than pressing a green button to make something dangerous and a red button to make it safe o_O
 
Lucien Nunes

Lucien Nunes

-
Mentor
Esteemed
Arms
Delta supplies are still popular afloat which adds complexity when speccing certain types of kit, e.g. entertainment lighting dimmers that take 3-phase input but control single-phase outgoing circuits. One of my colleagues recently succeeded in altering the specs for a number of forthcoming cruise ships, to include extra star-connected substation transformers for this application.
 

Reply to Practicality of 400 volt equipment in the Electrical Forum area at ElectriciansForums.net

Top Bottom