265VAC mains voltages are often seen in remote locations of developed countries?

[treez]

In certain parts of any developed country, there are remote areas where there is no point in having a power station anywhere near them….because there are too few people…(however, often busy motorways may go through such areas).

The generator is therefore distant, but The voltage has to be high enough at the generator…….ie, high enough that it can supply the maximum load in the remote area without dropping much below 240VAC (220VAC in Mainland Europe)….So then the voltage at the generator is often increased to 265VAC so that after the line voltage drops, the voltage will still be 240VAC at the remote area……………………however at night times etc, the load is low, and so therefore one sees voltages of 265VAC in such remote locations…. Would you agree?

 

[Easy peasy]

No - look up on-load tap changers for distribution transformers ...

 

[BradtheRad]

Grid power goes long distances at thousands of volts, then is stepped down by a transformer close to our house. If we're in a remote location I suppose the lineman might select a +10% tap on the transformer (which appears to be what Easy refers to above), in order to make up for unpredictable conditions. 265 V is ten percent greater than 240.

 

[treez]

Thanks, for the On load tap changer to operate, as you know, it must sense the VAC, then adjust the tap as appropriate. So the VAC voltage would go up to X volts, then the Tap changer would operate.

The golden question is then, for how long does the mains spend at the “too-high” voltage before the on load tap changer operates?

We had a Littelfuse rep saying that once in every 20 years, the mains goes up to 284VAC. (He didn’t say for how long this happens though).

The piece of info that cannot be found anywhere, is the mains voltage excursions outside 230 to 250VAC, (210 to 230VAC in mainland Europe) and for how long they last…….and finding this info for where the biggest violation occurs in whichever country.

Another Edaboard member very kindly sent me some data on mains voltage excursions at one outlet for a City in Germany. It was amazingly well regulated. It would be great if one could find such data for the worst case area of a developed country. (ie where the mains is most variant)


To think that all these engineers designing power supplies for mains operation...and they cant really know what is the true range of the mains input voltage to their power supply.

 

[betwixt]

I think my location would qualify as 'remote', the nearest power generator other than a few solar farms is a hydro scheme about 70Km away. My electricity arrives in the small village here at 11.5KV three phase through overhead lines then gets dropped to 250VAC at the local transformer. I have a direct 3-phase plus Neutral feed from that transformer which is about 100m away. The voltage here does fluctuate but generally stays within 250V - 255V range. There is no tap changer at the local transformer and it supplies about 100 properties in the village.

Where a tap changer is installed, I would guess it would respond very quickly, probably in less than one second.

Brian.

 

[BradtheRad]

once in every 20 years

My house had 10 percent higher mains voltage for a while, when power returned after a blackout brought on by a severe storm. My power inverter refused to start charging my battery bank. Yet the system worked fine as backup power for the house during the blackout.
I measured our mains as 135V. (Normally it was consistently 120-125.) Later our house voltage returned to normal.

In my mind I speculated that the electric company temporarily ran their generator voltage up, to maintain normal AC as multitudes of homes required excessive power suddenly after the blackout.

 

[c_mitra]

……………………however at night times etc, the load is low, and so therefore one sees voltages of 265VAC in such remote locations…. Would you agree?

Yes, This is a quite common here India even if it is not so remote. The University here is supplied with 66KV local substation and the local power comes from two 400KVA transformers. At night most of the instruments are off and the load on the air-conditioners are minimal the voltage goes up. Now we are setting up transformers close to the departments and the labs that need lots of power but the spike in voltage at night time has not gone away. So we are forced to install voltage stabilizers for individual labs for sensitive instruments.

 

[Easy peasy]

We design for 275Vac continuous and turn off at 300Vac ( 425VDC pk ) - this is the easiest way.

 

[treez]

We design for 275Vac continuous and turn off at 300Vac ( 425VDC pk ) - this is the easiest way.

Thanks, but crikey, there are some offline PFC’d flybacks which feature a 1.5SMC440A TVS after the diode bridge…and 425V peak is going to bring that into conduction…with a possible bang.

I always like to think in PFC'd flybacks, one can protect the fet from overvoltage ringing at switch on, by using a TVS across the HV DC bus...but with occurence of 300VAC...the use of TVS's would be no good.

1.5SMC440A datasheet
https://www.littelfuse.com/~/media/...littelfuse_tvs_diode_1_5smc_datasheet.pdf.pdf

 

[c_mitra]

We design for 275Vac continuous and turn off at 300Vac ( 425VDC pk ) - this is the easiest way.

We had instruments from Japan that will not run (reliably) at 240V - I figured out that they had transformers with taps at 200, 220,240 and 260V- I had to select the tap at 240V. They are XY recorders, scopes and potentiostats. Both the design and constructions were very robust- they rarely gave problems.