Why are the pump motors 3-phase?

[Bob Kinner KE8VU]

At the beginning of the tour (UN Day, 2023), we are shown transformers to convert 2-phase to 3-phase power for various motors. I understand that 2-phase was the prevailing transmission system of that day. So why are the motors running on 3-phase? Wouldn’t it have been simpler to run everything on 2-phase?

Ämne

[AlexanderSAQ]

Bob;
Thanks for your question about the 3-phase motors.
The 2-phase system was initially the most common power system in Schenectady NY, USA where Ernst FW Alexanderson worked and developed his alternator. When the 3-phase system later was taking over, General Electric and Alexanderson could not financially justify the redesign of the very complex speed control system from 2-phase to 3-phase and therefore kept it 2-phase for the main drive motor. However to change all the small drive motors for water cooling, rheostat circulation an so on, from 2-phase to 3-phase was an easy task.
In the late 1890´s the Westinghouse engineer Charles Scott developed a three-phase transformer that allowed for easy conversion of 2-phase to 3-phase or the reverse.
At Grimeton radio station we have a large 50kV – 2.3kV Scott-connected transformer in the external transformer building, which is supplying the drive motor with its 2-phase power. Inside the transmitter building there is a much smaller 2.3kV – 440V Scott connected transformer which will convert the 2-phase back to 3-phase for supply to all the small motors in the system.

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