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Question:

What is the benefit of having an electric generator coupled to the electric motor?

I noticed that most elevators are powered not by an electric motor, but by an electric motor-generator set. Does the generator really put out enough current to make up for the friction losses?Or is the generator used for powering lights and stuff? If so, why not use inverters or some smaller, cheaper means of creating a smaller current for the lights?

Answer:

NO BENEFIT ! IT CAUSES EXTRA LOAD TO MOTOR !!
Also so you can get electricity back when lowering the elevator...
That was the old way of powering the elevator. They needed to smoothly start and stop the elevator, and at the time, there was no way to control an ac motor with a variable speed. Only dc motors could start and stop smoothly based on the amount of current available. So the solution was to couple the ac motor, running all the time, to a dc generator whose field could be varied thus controlling the output current. This current was sent to the dc hoist motor, lifting the elevator smoothly, the operator controlling the field current of the generator to control elevator speed. Lights were never controlled by the generator, they just ran off the available ac supply directly. The generator does put out enough to overcome any friction losses in the system, but notice that there are counterweights on wire ropes to counterbalance the elevator car. Therefore, not as much power is used to raise and lower the elevator.
They use that to change the voltage.

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