The transformers of 400/33kV, 160MVA & 125MVA rating should be avoided as practice of using such low MVA rating transformers are not desirable at 400kV level. It is desirable that Transformers of above ratings are only procured by utilities to have standard ratings across the country. Can anyone explain why this is?
Not totally related but if you look at the UK national grid map then
A) there are not that many 400kV lines, and
B) except in high population centres or near to power stations (London, Southampton etc) The 400kV transformer stations (blue dots) are more or less uniformly spread.
The spacing distance is voltage dependent. The load areas can then be estimated as similar nos of square miles around each one. The red dots - 270kv lines and transformers are closer, spacing reduced almost, but not quite, proportional to voltage, and the area served (and therefore power handling needed) changes more or less as square of voltage.
An 11 or 33kV line will have proportionally smaller reach again, there are far more of them than fit on a UK scale map, and they each carry less power. DNOs publish their own maps for these.
As a very noddy rule of thumb the line voltage is at or near the maximum economic line length in metres. 400v going 400 metres is probably becoming worth investing in transformers and stepping up for all but very small loads.
Very few 11kV lines are much more than 11km long, 33kV lines 30km long etc. It can always be done with oversized cables of course, but the losses and rising costs to install mean it is getting uneconomic not to consider the higher voltage.
Mike
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