Can any one tell me how you calculate electricity,?

3 phases are vectors at 120 degree to each other and phase to phase voltage is : Sqrt(3)*240V = 415.69V

The old values of voltage in the UK where 240V single phase and 415 Volt between any 2 phases In 1995 it was decided to change the tolerances and re-designate the nominal voltages in UK to 230 Volt single phase and 400 Volts this was part of the harmonisation process with Europe.

Now to understand 3 phase generation think of a clock face with 3 hands of equal length all fastened together so they all rotate together. The length of each hand from the centre is equal to 230 Volts

Now with one hand pointing to 12 next pointing to 4 and the last pointing to 8 this represents the 3 phases at 120 degrees apart. Now draw a line from the tip of each of the 12 hand to the tip of the 8 hand now draw a line from the tip of the 8 hand to the tip of the 4 hand and finally from the tip of the 4 hand to the 12 hand this should now give an equilateral triangle. The length of each side of the triangle represents the 400 Volts between phases

This drawing also represents the 2 ways of connecting 3 phase loads namely STAR which is the 3 hands of the clock. The second connection is DELTA represented by the three diagonals connecting the tips together.

Draw a clock face and put in the lines as described above and also read all the other answers it should make more sense then.

The wheel analogy is quite a good one.

You are right, 3x240 is not 415V using pure maths.

To make 3 phase electricity, you generate each phase equally spaced in time (50 cycles a second), imagine each cycle taking a time of 1, then phase 1 will be at 240V at 0, phase 2 at 240V at 1/3 and phase 3 at 2/3, then back to phase 1 at 1 - if that makes sense. In between going from 240V peaks, the phase goes to -ve 240V and everything in between down and up. As one is at 240V, the other 2 are not at -240V, but somewhere between 0 and -240V.

When the difference in volts between 2 phases is added together, this gives you the 415V, and mathematically it is 415V (240 x sqrt 3)

Hope this sort of makes sense.

Now to add a bit more to it, if you add al 3 together, then the total volts is 0!! This is because of the cyclical effect, as one is at 240V, the other 2 are at -ve volts which added together makes 0V. This is useful in power generation - if all three phases are equally loaded then you don't need an earth cable so power transmission lines are cheaper to transmit 3 phases rather than single or 4 phase for the amount of energy transmitted, or at least a small earth cable compared to the phase cables

3 x 240V as Three Phase gives about 415V; or more correctly a single phase of a 415V system measures about 240V.

The three phases are each 120' or a third of a cycle out of step, so as each reaches it's peak the other two are both half way between peaks.

The simplest visualisation is to think of a wheel with three equal spokes and no rim. The tips of the spokes represent the voltages on the three phases. As it turns, each goes equally above and below 0V (the hub).

Each spoke length represents 240V, but if you stand it with two spokes down and the third upwards, the total height (voltage) is not double, because the two lower spokes are spread out at angles.