An interesting excerpt:
The Adams plant supplied two-phase 2200V local service as well as three-phase service to Buffalo via 11kV lines (two-phase power, produced by the generators, was converted to three-phase by a 'Scott Transformer' and sent to Buffalo that way).
There were a number of 25 Hz plants and I believe that some of them generated 3 phase 25 Hz.
I remember a paper I read years ago. I think you would have found it interesting.
A plant was using 25 Hz induction furnaces.
The power supplier was phasing out 25 Hz service.
An alternative was sought to the cost of converting the induction furnaces to 60 Hz.
The plant had a number of surplus 25 Hz synchronous motors
It was proposed to use 60 Hz synchronous motors to turn 25 Hz synchronous motors through appropriate ratios to generate 25 Hz to power the 25 Hz furnaces.
Second issue; The plant owned supply of 25 Hz motors did not include any single motor with enough capacity to supply the furnaces.
It was proposed to run two or more sets in parallel to gain the needed capacity.
Next issue; Paralleling. Generally the prime mover supplies torque and the parallel connection locks in the speed and angular position.
However, with synchronous motors driving synchronous generators, the angular position of the rotors becomes important. If the angular position of one rotor lags a few degrees that set will not carry its share of the load. If it lags a few degrees more, it will be driven or "motored".
This problem was solved by fabricating what the engineers called a micrometer coupling. This was a coupling with an adjustable driving link. The sets were started and the synchroscope was observed. The synchroscope would show the electrical angle error between the two sets. The set would be stopped and the relationship between the driving rotor and the driven rotor adjusted with the micrometer coupling. The procedure was repeated until good load sharing was achieved.
Bill
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"Why not the best?"
Jimmy Carter