UK mains voltage

quoia

If you look at the mains supply with an oscilloscope you will almost certainly see a near perfect sine wave with a peak voltage of around 325 volts. (if the power stations are pushing the 230V up to the max of 253V then this peak can reach 360V !)

Roughly Vrms = 0.7 × Vpeak and Vpeak = 1.4 × Vrms


Actually the "1.4" is the square root of 2 which = 1.4142135623730950488016887242097....

MGAstra

Hi quoia,

Do you know where jack_pot got the 1.1107 from? I've never heard of this before!

I get the sqrt2 business and the 0.70710678118654752440084436210485... from
1/(sqrt2)

The shape of the waveform of mains depends on the appliances its loading. PC's and TV's etc all have SMPS which will certainly bring down the peak of mains. I'm not saying it will be a square wave! If you and your neighbours aren't loading it with lots of appliances with SMPS, then sure it will be almost perfect square wave.

It is due to this peak smoothing of an inital 50Hz sine wave that produces the 3rd 5th 7th (etc) harmonics at 150Hz 250Hz 350Hz etc.

quoia

MGAstra wrote:

Hi quoia,

Do you know where jack_pot got the 1.1107 from? I've never heard of this before!
................
If you and your neighbours aren't loading it with lots of appliances with SMPS, then sure it will be almost perfect square wave.
.

1.1107 ? No idea !

"square wave" ? Hope you meant SINE wave !

MGAstra

Yes I actually meant SINE WAVE in that quote above!!

Still wondering about 1.1107

I've heard of 'form factor' refferred to before, but to be honest I'm not farmillir with that terminallogy!

[Deleted User]

1.1107 is the form factor for a sine wave (or strictly speaking a full wave rectified sine).

Form factor is the ratio of the RMS to the mean value of a wave form.
For a sine,
the RMS is 2^-1/2 =0.7071
and
the mean is 2/pi =0.6366
so
the form factor for a sine is 0.7071/0.6366 =1.1107.

If using a mean-sensing meter on a non sine waveform, you divide the reading by the form factor for a sine, and multiply by the form factor for the waveform you're measuring to get the RMS.

dazzzyc

bloody hell theres some clever people using this forum

sweep9

Get 'em talking about 415v phased input supply into commercial premises!!!