Yesterday I wrote a pretty awful post about why I didn’t consider the government’s decision to encourage owners of diesel generators to prop up the National grid, in times of power shortage.
I spent most of that post banging on about frequency and load sharing. I should have added another factor I think it’s a laughable idea.
Voltage.
In our houses in the UK the standard voltage used is 230V. This is a very low voltage in the great scheme of things but it is reasonably safe. If you touch an exposed wire it will make you remember it but unlikely to come to harm from it.
Not so the National Grid. This has sections that transmit at 400 kV (400,000 V). The simple reasoning is the formula taught in basic science classes. E=IR, where E is the voltage, I is current, and R is resistance. Even the best conductors in normal use today have their limitations. It would be infeasible to try and transfer electrical energy at household voltage. The cables would have to be huge in diameter. Therefore the high voltages.
Now in the Hospital, public building, brothel, etc, it is not realistic to generate at those sort of voltages as there is only a very short transmission distance. Therefore it is most likely that they will generate at 440V(I’m going with my own experience here) for heavy power usage such as industrial heating systems and pumps. For general use it will be transformed down to 230V.
In short you have two totally incompatible voltages which you have to tie together with transformers and their losses, to make a back feed situation work.
Can it work? you tell me.
*Bought more candles*
I may post about the death and destruction that could be wrought.
Good point. Although transformers WILL work in reverse (ie in your case boosting from 230/415 volts up to HV they aren't happy about it. I'm basing this on my own "experiments" over the years - how these would relate to MW's instead of a few tens of watts I can only imagine!
ReplyDeleteAs for as the purpose built "Genset Farms" that are springing up, this shouldn't be a problem, as they are only intended to supply the grid, unlike the proposed hospital back-up sets. It strikes me that the only sensible way those could be used in times of high demand would be to run them solely to supply the sites they're installed at, and thereby relieve that amount of load from the grid. Of course they are no longer "Standby" sets then.
Another thought - it's very likely that the new sets being installed will have latest generation "Common Rail" diesel engines (to comply with upcoming emission regulations). These, at least, should be easier to integrate into the grid, and control accurately. Like you I can't see a traditional mechanically injected unit lasting very long...
And all that applies to f'ing windmills too. The generators in those things will only be turning out (at a guess) 35KVA at 415V ( depending on how the wind blows). The losses in stepping that up to grid power must be huge.
ReplyDeletePerhaps they are DC generators? Even so a nightmare and the conditioning of the electricity will be very wasteful indeed.
Modern control circuits should make the connections easier. It might even be better to generate dc and feed it to the grid via an inverter - after all the 1,000,000V (at 1000A, i.e., 1GW) power transfer connections between the UK and France (& also The Netherlands?) must use efficient conversions.
ReplyDeleteI think the electronics will be developed to support robustly this multi-small-generator-backup concept.
See here & posts earlier
Deletehttp://www.eureferendum.com/blogview.aspx?blogno=84224
Image the in-rush current on those transformers. Awesome!!
ReplyDeleteIt works for solar cells to feed into the grid so I guess it would for generators. Although that doesn't stop it being a stupid idea!
ReplyDeleteE=IR?
ReplyDeleteI was taught that it was V=IR,why have they changed it?
When I was at school it was V. Then some bright spark decided to use EMF instead. Electro Motive Force.
DeleteOh dear, oh dear, oh dear, filthy engineer, where has your engineering knowledge gone?
ReplyDelete440V 3 phase IS THE SAME AS 230V single phase.
Back to school. Generating 3 separate voltages at 120 degrees to each other, 440 volts from phase to neutral. This is 440v 3 phase, as used in industry and other power users. Now connect from one phase to another and the difference is 230V. Voila! That's household power.
No transforming required.
Utter rubbish. In the UK domestic distribution is 3 phase 4 wire. So it's 415v phase to phase and 240v phase to Earth/neutral at the local 11kV transformer..........
Delete@ SimonJ - If you're going to be pedantic at least get your facts straight.
ReplyDeleteIn a 3 phase system the phase to phase voltage is higher than the phase to neutral voltage - completely the opposite of what you said above. And the conversion factor is the square root of 3 or 1.732.
So for a 230 volt single phase system the corresponding 3 phase value is 400 volts NOT 440.
Yeah, yeah, ok, so I got it round the wrong way. I wasn't 100% sure which way round, so I winged it with a 50:50 chance. In my defence, I'm a mechanical engineer who works with my electrical engineering colleagues! And the volts, yes, it used to be 415/240, so couldn't be 440/230.
DeleteBut I'm still shocked that our host and 8 or so commenters hadn't twigged.
No problems - apology accepted. The change from 240 to 230 is another bit of EU mandated fuckwittery, and is only happening gradually as older equipment is replaced. As I type this our household mains is showing 240.4 volts on a digital meter...
DeleteI can't remember where the 440 volts figure came from - that would equate to 254 volts single phase. Perhaps it was back in the mists of time when supply regulation wasn't so good?
I look after various equipment at a friends farm. I discovered that his old standby genset had a dodgy AVR, and was chucking out nearly 270/465 volts! The motors and lights didn't mind, but some expensive control systems certainly did...
I should have made it clear. The 440 I was referring to was the voltage we use on ships. Incidentally we also worked with a frequency of 60 Hz rather than 50Hz.
Delete60Hz suggests an American influence?
DeleteWow, lots of engineers all in one place... Energy production is constantly in the news eh.
ReplyDeleteWould you guys do me a favour, and check out this motor design?
http://www.overunity.com/13692/core-rearrangement-fin-motor-open-tech-ou/
Would it work?