Why the voltage between phase to neutral is 240v compared to phase to phase is 415v?

Answer 1

What you are describing is a three-phase, four-wire, system having a phase voltage of 240 V and corresponding line voltage of 415 V.

You do not add the three phase voltages (3 x 240 = 720 V) to obtain a line voltage.

The three phase voltages are actually displaced from each other by 120 electrical degrees, so any pair of phase voltages must be vectorially-added to obtain a line voltage. If you perform this calculation, you will find that the line voltage is always 1.732 times larger than the phase voltage. So, 1.732 x 240 = 415 V.

Answer 2

In a three-phase, star- (or wye-) connected, system the line voltage (line-to-line voltage) is 1.732 (or the square-root of 3) times the phase voltage (line-to-neutral voltage). The reason for this is that a line voltage is the vectorial sum (not algebraic sum) of two phase voltages displaced from each other at 60 degrees.

These days, incidentally, the UK's nominal phase voltage is 230 V, and its corresponding line voltage is 400 V.

Answer 3

Because a 230-V single phase supply is obtained from a 400-V (not 415-V) three-phase supply -not the other way around!

You would need to obtain two additional phase voltages, displaced by 120 electrical degrees -this is only available from a three-phase machine.

Answer 4

There is no such thing as a 440/240-V three-phase system.

If 240 V is the phase voltage, then the line voltage will be 415 V. If 440 V is the line voltage, then the phase voltage will be 254 V.

Answer 5

Single phase can be 120v, or 220 volts, and 3 phase can be 120v or 208 volts, the only way to get 440 volts is to use a step up transformer to convert the 208 volts to 440 volts (ac)

Single phane and three phase is how the transformer transforms the electricity from the high voltage line In single phase service there are 2 lines coming into the building, Hot, Neutral, and there is no shift in the phase because there is only one "hot" wire. Now 3 phase has 3 lines, Hot, Hot, and Hot, however each line is 120 degrees out of phase with each other. If you look at any motor in a single phase supplied building they will have capacitors on them, this it to create a phase shift, otherwise the motor will not rotate, however a 3 phase supplied building the motors will not have any capacitors because the 3 lines already has a 120 degree shift in their phases. It is complicated unless you take a class on electricity and or motor controls then it gets a lot easier to understand

Answer 6

I notice that 720 V is exactly three times 240 V, so you are describing a 415/240-V three-phase, four-wire, system. With a three-phase, four-wire, system there are four conductors: three 'hot' conductors which are called 'line conductors', and one 'neutral conductor'. The voltage between any one of the three line conductors and the neutral conductor is called a 'phase voltage' and is 240 V. The voltage between any pair of line conductors is called a 'line voltage', and is equal to 1.732 times the phase voltage -i.e. 415 V. The reason for this is that a line voltage is the vector sum (not the algebraic sum) of a pair of phase voltages which are displaced by 120 electrical degrees. If you add two phasors (vectors) that are 120 degrees apart, the resulting phasor is 1.732 times larger.

The voltages you describe, 415/240 V are no longer the nominal voltages for the UK, having been replaced by 400/230 V in support of 'EU harmonisation'!

Answer 7

This is a three phase four wire system. The three phase voltage is 415 volts. To find the star point voltage divide 415 x 1.73 = 239.8 or 240 volts.