Answer for UK, Europe and countries running a 50 Hz supply service.
By custom voltages between 400 and 440 v are used in Europe for 3-phase supplies to consumers. A transformer of up to 1000 kVA with a secondary voltage in this range would be used to supply a street in a town or city, with each property given a single-phase supply connected between one line and neutral of the 3-phase circuit.
Yes 230 volts is classed as single phase but it is not the only single phase voltage. If you take any two legs from a three phase system, the voltage from these legs is also classed as single phase. The 230 volt single phase is the output of a transformer whose primary is one leg of a three phase primary high voltage system. The 230 volt secondary is center tapped to give 115 volts before the tap and 115 volts after the tap, hence the common voltage of 115/230 that is used in North America.
These voltages are both wye connection three phase voltages. The voltage difference comes from the primary three phase voltage supplies. 277 volts is obtained from 277 x 1.73 = 480 and 240 volts is obtained from 240 x 1.73 = 415. 480/277 volts is a common three phase American voltage. 415/240 volts is a European voltage. In Canada a common three phase voltage is 347/600. The 240 volts could also be a single phase voltage in North America derived from a split phase secondary on a distribution transformer that supplies 120/240 volts to homes.
The process of obtaining 220 volts from 380 volts is quite simple. 380 volts is a three phase four wire system voltage. The 220 volts is obtained by taking the sq. root of 3 which equals 1.73 and dividing it into the phase voltage. 380/1.73 = 220 volts. This holds true with any three phase four wire voltage system. 208/1.73 = 120 volts, 415/1.73 = 230 volts, 480/1.73 = 277 volts and 600/1.73 = 347 volts. This lower voltage is present on any of the three phase legs of the three phase system to the neutral which is grounded on a wye connection.
Let's get the terminology correct. A 'phase voltage' is measured across a phase, whereas a line voltage is measured between two lines. So there is no such thing as a 'phase to phase' voltage -it's a line to line voltage (hence the term 'line voltage').
A source of 208 volts can be obtained from any two legs of a three phase four wire 208 volt system. The two legs are classed as single phase 208 volts. The lead tags can be L1-L2, L2-L3, or L3-L1 all of which will give you 208 volts. Any of these lead tags to the grounded star point (wye) will give you 120 volts.
In three-phase there are three live wires and a neutral. The voltage of a three-phase system is always quoted as the live-to-live voltage, and the voltage from one live wire to neutral is 57.7% of that. A 440 v 3-ph system has 254 volts between live and neutral. <<>> The question statement is not correct. Two legs from a three phase three wire 440 volt system will still be 440 but classed a single phase. On a three phase four wire system supply, the voltages will be determined by the following equation. 440/(square root of 3) 1.73 = 254 volts. The second single phase voltage attainable from this source connection is any one of the three phase legs to grounded neutral center point. This is known as a wye or star point connected voltage supply. To obtain a 220 volt single phase voltage, the three phase system would have to have a voltage of 220 x 1.73 = 380 volts.
A voltage of 380 volts is a three phase voltage. On a three phase four wire system, each phase leg to neutral (grounded) will give you 220 volts. This voltage is obtained by dividing the phase voltage by 1.73, as the phase legs are generated 120 degrees from each other. Square root of three is 1.73 divided into 380 equals 220 volts.
600 volts between any two wires. The phase has nothing to do with voltages, only current relationship.
Nothing happens. This is a normal way to obtain a single phase system from a three phase system.
400 volt three phase on a grounded system is 230 volt single phase, with each phase 120 degrees apart. So, if you have a 400 volt, three phase four wire service (grounded service), you can pull one phase off and reference to the neutral for 230 volt service. Note this may not allow 115 volt service, unless there is also a center tap for each phase.
A three phase panel will not give you 110 and 220 volts. A three phase four wire panel will, but not at these voltages. The nearest voltages will be 120 and 208 volts. The 120 volt is the wye voltage of 208 volts. 208/1.73 = 120 volts. A single phase three wire panel will give you 110 and 220 volts.
The star point or wye voltage of a 480 volt three phase four wire system is 277 volts. The 480 voltage is divided by the sq root of 3 (for 3 phases). The sq root of 3 is 1.73. 480 volts/1.73 = 277 volts. The same formula is used on all three phase four wire systems. 208 volts /1.73 = 120 volts, 416 volts /1.73 = 240 volts, 600 volts / 1.73 = 347 volts.