# Why we use 3 phase power supply, not 4/5/6 phase

I’m unsure relating to the social science of multi-phase systems. It looks to American state that for every part added, the full power capability is multiplied by one line-ground voltage times one line current thus there’s no natural less-costly range of phases. , however the rationale for six-phases was that power transfer may be doubled employing a single six-phase cable on a strained right-of-way. it’s attention-grabbing that during a six-phase system, the line-to-line voltage is that the same because the line-to-ground voltage.

I think the important reason we tend to use three-phases lies with the force made by different systems. as an instance with a single-phase system, the force obligatory on motors and generators pulsates from zero to the most. this is often OK for little motors, however not for giant generators or motors.

With a balanced three-phase system, the motor or generator force could be a constant and therefore the shaft doesn’t perpetually upset periodic  torques.

An economic argument for 3-phase systems works once considering the value and quality of wiring motors and generators for quite three phases.

I have bother with the argument that that the 3-phase system needs less cross-sectional of wire to transmit power. allow us to inspect the recently projected reason with further range of phases:

Imagine that we’ve got 2/3/4/5/6 similar single-phase generators and 2/3/4/5/6 similar single-phase hundreds. Total cross-sectional space of wires are 2A/6A/8A/10A/12A (2/3/4/5/6 direct and 2/3/4/5/6 back-going lines). If we tend to unify going back lines into one, there’ll be total current 2I/3I/4I/5I/6I, wherever I is that the current of single direct line. If hundreds are an equivalent, then providing a shift of 180/120/90/72/60 degree between voltages we tend to get an equivalent shifts between equal currents. The total of returning currents are capable zero and we tend to  that we in theory haven’t any want in going back lines!!! therefore … we get power provide via cross-sectional space of 3/4/5/6 rather than 6/8/10/12.

Therefore, in every case, we tend to scale back the cross-sectional space by an element of 2. there’s nothing special concerning 3-phases once considering conductor cross-sectional space. additionally, if we tend to were to settle on the best system, it’d be 2-phase ( V across the neutral).

However, all part conductors share the come conductor. Thus, a 2-phase system would use 3 conductors to transmit 2pu power; a three-phase facility would use four conductors to transmit 3pu power; and a 6-phase system would use seven conductors to transmit 6pu power. That is, the a lot of phases, the cheaper cross-sectional space of conductors, as a result of a lot of phases share the value of the only come conductor.

As i discussed earlier, we decide 3-phase systems, as a result of the force of enormous 3-phase motors and generators is constant, avoiding periodic  torques, which might ruin massive motor or generator shafts.