KVA to amps help

[geordie]

Have got a new supply going in and have been told its 300KVA 3 phase now if i have worked it out correct is comes in a 433 amps which going by the size of the places i would expect to be per phase. Which i take it would be fused down to 400 amps by the DNO

 

[telectrix]

so, bigger and better things than a spark? when yo rulle the world? seig heil?

 

[davesparks]

Since when did a DNO transformer work at 433v?

For about the same amount of time they have been 250v

 

[Darkwood]

Haha always has to have a dig don't you? What relevance is that. For your info I was a electrician for over 8 years before moving onto bigger and better things.

Go on then, entertain us! What bigger and better things could their possibly be ?????

 

[Guest55]

Go on then, entertain us! What bigger and better things could their possibly be ?????

maybe............

 

[Knobhead]

I await atm84’s reply with baited breath.

He’s probably be better off burger flipping, all he has to do is blithely follow the instructions on the pack. He can’t mess the chips up, I know what was done to them before they reach the outlet.


atm84, eight years in the trade and you haven’t yet worked out that 400V is a work of fiction written jointly by the EU and the IET. In the UK it is totally impractical due to the massive installed infrastructure based on 433V.
It takes but a stroke of the pen to deem 400V as the public supply voltage. The engineering side realized it’s impossible and just ignored the directive. A classic case of it’s my bat and ball, I make the rules.

Some of the lads know of my experiments of lowering the voltage on a 80,000KVA system to 400V. It ended in total disaster and I put the voltage back to 433V pronto.

 

[Besoeker]

Measured at the input to our house.
Done with a digital scope and downloaded to an excel spreadsheet so I can do the number crunching.
It's the kind of thing I do for power quality analysis but this was just a bit of fun.

A couple of points are immediately evident if you are used to looking at these things.
The flattened peaks are indicative of harmonics, particularly third in this case. Typical on supplies in residential areas - all those electronic gizmos.

The other is the RMS voltage.
251V

V(av)	0.00
V(rms)	251.25

 

[Knobhead]

It would be interesting to see the effects of harmonics in the area I live, slap bang in the middle of student land. Many are Chinese or Japanese, PC’s, games consoles, you name it they’ll have it.

 

[Besoeker]

It would be interesting to see the effects of harmonics in the area I live, slap bang in the middle of student land. Many are Chinese or Japanese, PC’s, games consoles, you name it they’ll have it.

I've come across harmonics issues for quite some years now. My field is variable speed drives which are known generators of harmonics. Some these are in the MW range and upwards so harmonics are significant and predictable. Often these have to calculated, presented, and guaranteed at the bid stage - before any contract is placed. Rock and a hard place.

It is par for the course for us to have to include before and after compliance studies.
On one pumping station, in a mainly residential area, the before measurements were non-compliant before we commissioned the variable speed drives. And no worse afterwards.

Initially, that puzzled me. We'd put in some fairly big drives - total installed capacity was about 1 MVA. There was a local dedicated transformer for the sub - (11kV to nominally 400V) so the PCC was at 11kV. The harmonics were measured on the 11kV side.

The explanation isn't altogether complicated. Our drives were a mixture of six and 12-pulse units fed from the three-phase supply.These should result in harmonics no lower than 5th (250Hz).
The the analysis showed a high 3rd (150Hz) content. Single phase non-linear loads.

None very big. Just huge numbers of them and that swamped the contribution from our drives.
And that's what you see on my flat topped wavevorm.

 

[Doomed]

I read and understood ever word of that. Its just when you put the words into whole sentences I got confused.

 

[Besoeker]

I read and understood ever word of that. Its just when you put the words into whole sentences I got confused.

OK.
Huge numbers of single phase electronic gizmos add up to a lot of waveform distortion.