advantages of 3 phase as opposed to single phase?
advantages of 3 phase as opposed to single phase?
(OP)
what are the advantages of three phase system supply over single phase supply?
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advantages of 3 phase as opposed to single phase?
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RE: advantages of 3 phase as opposed to single phase?
RE: advantages of 3 phase as opposed to single phase?
If you need a few lamps only and perhaps a fridge and a TV set - then single phase is OK.
Gunnar Englund
www.gke.org
RE: advantages of 3 phase as opposed to single phase?
A single-phase induction motor isn't as efficient and has capacitors and speed switches that are prone to fail.
RE: advantages of 3 phase as opposed to single phase?
RE: advantages of 3 phase as opposed to single phase?
1: because of motor pole geometry, three phase motors are self starting and do not require such adders such as split phase starting, capacitor starting or shaded pole starting. This becomes critical at higher horsepower levels and generally at about 7.5 hp one starts thinking 3 phase.
2: on a balanced 3 phase distribution system, the phases will cancel at the load and you do not need to consider return current to the source. No return path voltage drop (potential rise) and no return path I2R losses.
RE: advantages of 3 phase as opposed to single phase?
Expanding on the comments of thread238-139362, it is not only the voltage that never goes to zero, but rather that the instantaneous power supplied is constant with three phase. In single phase the instantaneous power goes to zero, meaning that something has to store power if the load needs instantaneous power.
In singe phase rectifiers this means the larger capacitor/inductors have to store enough energy to supply the load while the source is at zero power. In three phase rectifiers the capacitors/inductors only have to store enough energy to ride through commutations.
In motors, the energy is stored in the rotation of the machine. Unfortunately, if the machine stops at a point where the load requires more power to start moving than the single phase motor can supply instantaneously, it will not turn. The devices Electic mentions are energy storage devices. They allow some of the energy to be stored electrically for those times when the load average power exceeds supply instantaneous power.
Triplen harmonics cancel in a three phase system.
On some applications more than 3 phases are beneficial. 12 pulse rectifiers even use 6 phases so that more harmonics also cancel. I also heard about a experimental six phase transmission line used so that the electromagnetic fields would cancel out and be below some threshold on a narrow right of way.
RE: advantages of 3 phase as opposed to single phase?
Triplens are the harmonics that always ADD in a three phase system.
RE: advantages of 3 phase as opposed to single phase?
Triplen currents add in the neutral if non-linear loads are connected from phases to neutral. That is where you are right.
Triplen voltages cancel in a three-phase system when voltage is measured phase-phase. That's where you are wrong.
Gunnar Englund
www.gke.org
RE: advantages of 3 phase as opposed to single phase?
RE: advantages of 3 phase as opposed to single phase?
RE: advantages of 3 phase as opposed to single phase?
That is valid for all harmonics with 3xN frequency. The reason is that Nx3x120 degrees is Nx360 degrees. So the harmonics have the same phase angles in all three phases.
Gunnar Englund
www.gke.org
RE: advantages of 3 phase as opposed to single phase?
3 phase power delivers energy more efficiently than 1 phase:
A 4-wire 3 phase system, if reasonably balanced, delivers approximately 3 times the power for only 2 times the conductors (single phase must have 2 wires), while only experiencing half of the voltage drop (as neutral only carries the vector sum of the 3 phases, which should be near zero, and Ohm's law shows that negligible current = negligible voltage drop on the return path).
So, for the same guages of cables, twice the conductors allow triple the power for half of the voltage drop over a given distance,
or
A (4 wire) three phase system can carry 150% more energy than a (2 wire) single phase system, using wires with only half as much current-carrying material (i.e. smaller guages) over the same distance.
A three-wire 3 phase system can be even more efficient, but comes with its own drawbacks.
This is over and above the 'power usage' advantages described above.