The reason for limiting power transmission & distribution to 3 Phases (instead of 6 Phases or 9 Phases or further) by varying the electrical phase shifts is due to the increase in cost of Circuit Breakers and Copper Busbars & Busducts.
When and how can we expect distribution to be multi-phase ?
Will this change be significant ?
A six-phase power line configuration reduces the measured intensity of electric and magnetic fields that are associated with transmitting AC electric power
http://www.physicsforums.com
Recently, there is a growing interest on the concept of six phase transmission as an alternative to the voltage up gradation of a line, to increase the power transfer capability within the existing rights of way. This paper mainly deals with the transient stability analysis of a 3-phase double circuit line in comparison with that of
equivalent 6-phase transmission line. A smart grid is a grid that is capable of delivering electricity from suppliers to consumers via a two-way digital technology, effectively controlling the consumers energy consumption by reducing the cost of generation and transmission and hence to improve the system performance,
efficiency and reliability. A framework for cohesive integration of smart grid and six phase transmission technologies facilitates convergence of highly needed standards and implementation of necessary analytical capabilities. This paper critically reviews the reliability impacts of smart grid resources and transient stability
of six phase transmission. We observe that an ideal mix of these resources leads to a better stability that eventually accentuates reliability challenges further
Investigation on Transient Stability of Six-Phase Transmission
System and Proposal for Integrating with Smart Grid
T.Charan Singh , ,K. Raghu Ram ,,B.V. Sanker Ram , P.S.Subramanyam
The International Journal Of Engineering And Science (IJES);ISSN (e): 2319 – 1813 ISSN (p): 2319 – 1805; Pages || 31-40 || 2014 ||
www.theijes.com/papers/ICIEEE/E031040.pdf
The real reason behind the 3-phase system is the constant instantaneous power. If you can asume balanced loads the 3-phase power is only dependent on the phase angle of the balanced current, instead time dependent. Please take a look to this link, specially to the equations that I attached to you.
http://en.wikipedia.org/wiki/Three-phase#Constant_power_transfer
I never solved the equations for a 6-phase system but I asume that from the point of view of power transference it is unnecessary, and maybe a 6 or 9-phase system will suffer of the same problems of a 3-phase system regarding harmonics, unbalances, etc.
Cheers.
For a given power transfer, with a given line-to-neutral voltage, the total cross section of conductor needed is the same for 3- or 6-phase system. On the other hand, the cost of insulation, fuse, switchgear, cables, etc for 6 lines is higher than 3. 6-line system however has a specific benefit in reducing line reactance through parallel lines, which is lacking in 6-phase. Thus there does not appear any practical benefit for higher phase transmission system.
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