why 3 phase electricity instead of 4 or 5, etc?
In: 1
Its the happy medium
Single phase requires two thick conductors to deliver the power. If you do 1000V phase to ground and 100 amps you get 100kW with 2 thick cables
Three phase is three thick ones and one thin neutral (or no neutral if you Delta it). If you stick with 1000V phase to ground and 100 amps per phase you now get 300kW and only 3 thick cables so that’s a 2x improvement in power delivered per wire cost
You could easily do 6 phases but it doesn’t actually help anything.
Once you’re to the point where you have multiple balanced hot phases then each wire is carrying full current and you don’t have any wires wasted on neutral. If you did 6 phases at 1000V phase to ground and 100A each you could deliver 600 kW but it would take 6 wires so its the same power delivered per wire(100kW) as 3 phase.
Big motors and generators are almost always wound as 12 pole. You could increase the number of poles but this mostly increases the speed of the motor and not the efficiency. An industrial sized 3 phase 480V or higher AC motor is already 98% efficient or higher, the big generators used in power stations are 99%. More phases would increase the complexity of the motor but there’s no efficiency left to get.
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