Quote:
Originally Posted by broadgage
Actually changing transformer tappings throughout a country would be a huge undertaking, and I doubt that it will happen.
However the reports of increased voltages in mainland Europe suggest that it may be happening in some places.
Perhaps new transformers are being set to 240 volts at the transformer, to achieve about 230 on average at the load.
Of course an adjustment could be made over a very large area by leaving the local transformers alone, but slightly increasing the high voltage transmission voltage. Increasing the nominal 66KV up to 69KV would do it, presuming that all the downstream transformers will be happy with an input about 4.5% high.
In the UK, transformers are normally set at about 250 volts, so as to achieve about 240 on average at the customer. The nearest customer would get about 250 volts and the most distant about 230, with 240 being an average.
In London, no piecemeal voltage increases could be done without a lot of trouble. Many substation transformers are paralleled on the LV side with others nearby. So they can't be altered one at a time.
And even transformers not normally paralleled may be so connected during breakdowns, so the voltages need to match.
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Transformers used in EHV systems have many taps (possibly 20) where the Voltage can be varied in small increments. Indeed, there are monitoring systems that will automatically change the setting but remember this has to be done on load so it is a complex mechanical device.
Remember also that EHV systems employ overhead line networks and that expensive distance protection is provided. These systems will invariably require fault impedance Voltage measurement.
From a domestic viewpoint there are literally thousands of 6600V/433V nominal distribution transformers scattered around the UK. The majority of these units will have manually adjusted off load taps that are 2.5%, 5% & 7.5%. It follows that the Voltage could vary on a daily basis and that measurements at a socket may be different to ones next door neighbour.
Note that automatic telephonically operated taps may have only recently been introduced as I worked on the original designs as late as 2005.
Saying all that there are annoying issues in so far as tungsten filament lamps that used to be rated 250V. Following harmonisation they became 220V which meant a reduction in life coupled with a substantial increase in sales for the suppliers?