2-phase power at Adams Power Station, Niagara Falls (14 - Electricity Distribution)

They used 2-phase power at Powerhouse #1 at the Adams Power Station at Niagara in 1895. In this obsolete form of electricity distribution, the two phases are ninety degrees apart.
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[@Jota_VA]

Scott-T Transformers please 🙏🏽

[@johnburns4017]

So _two_ phase generators? Only two coils in the generator?

[@dmmartindale]

Apparently.
Two phases 90 degrees apart gives many of the same advantages as 3 phases 120 degrees apart: the total power drawn from the generator, and created in the motor, is constant - there is no variation in torque. However, transmission requires either 4 wires, or 3 wires where the wire common to the two phases has to carry extra voltage, and the voltage difference between the other two wires is higher. The advantage of 3-phase power is that the sum of the 3 phase voltages is zero, so the power can be carried on just 3 wires, all of which have the same current (and thus wire diameter) and voltage. So the added complexity of the generators, motors, and transformers (which need 3 coils instead of 2) is offset by the simpler power distribution of 3 phase.