OK

I'm afraid that this is rather a complicated area - hope the following is not too over-the-top

Electricity in England is generated as 3-phase. Each phase changes its voltage amplitude in time in a sinewave pattern and the amplitude at a given time can be described by the following equation

V*Sin(omega * t) + phi where omega is 2 *pi*f (f= frequency = 50Hz), t is time and phi is the phase angle

A single waveform will curve up from zero V to fully positive V, down to zero V again and then down to fully negative V and up again to zero V in a given time and this is defind as one cycle

Mains electricity in UK has

**50 cycles per second (Hz)**). Each cycle is defined as a rotation of 2*pi radians which is

**360 degrees**.

For three phase, we generate 3 of these sinewave voltages at

** 120 degrees apart**, thus, for example, the first (red phase) will pass through zero V at

**0 degrees**, the second sinewave (blue phase) will pass through zero for the first time at

**120 degrees **and the third sinewave (yellow phase) will pass through zero V at

**240 degrees**.

Three phase waveforms looks like this:

(any one of these plus a neutral is the the supply you get in your house) E is the voltage amplitude and for English distribution system would be 586.81 V peak (415V RMS)

All three phases are sent out to the sub stations. What the electricity board do is take a different (single) phase (Red, Blue or Yellow) + a neutral to each street and then to each house in that street. Phases are generally not mixed in a street and so all will be on red or all on yellow etc.

The

**240 V you know and love is the RMS **voltage between a single phase and Neutral

(RMS = Root Mean Squared = SQRT((Peak V * Peak V)/2)

Between ANY two phases we get an

**RMS voltage of 415V**. When all three phases are joined at the power station, the mid point = ZERO V and is the Neutral that you use in your house.

3-phase has a higher voltage and can deliver more power to a machine (there are other advantages, particularly for motor design but that's enough for now)

I will try to post some pictures tonight to clarify a little