The issue of relationship conversion between motors and generators

The original poster asked three questions: 1. If the speed of the turbine exceeds that of the motor, the motor must be in a power-generation mode. 2. I don’t understand this question. 3. The turbine helps the motor do work, so of course it saves energy

1. For a turbine-driven motor, I believe that the speed must be above the motor’s rated speed (but below the synchronous speed) in order to generate electricity. The speed must be greater than the synchronous speed in order to enter the power generation mode. (This is an asynchronous generator.) 2. Does the second question ask whether, if a turbine drives a motor but that motor is not connected to the power grid, it will be damaged? I think it shouldn’t be a problem for a short period of time, but running it like this for a long time isn’t good – it can easily cause the engine to overheat. 3. Turbine-driven motors can save energy even when they are still operating in motor mode; in fact, this is how they are used in many places.

When the motor’s speed exceeds its synchronous speed, it switches to generating electricity for external use; therefore, an external power source to drive the motor must be available

The relationship between the rotating magnetic field of the rotor of the electric machine (including motors and generators) and the rotating magnetic field generated by the stator determines whether it is in a power generation mode or an electric drive mode. The former is related to the speed of the motor, while the latter is related to the system. When the speed of the rotor’s rotating magnetic field is higher than that of the stator’s rotating magnetic field, in other words, when the prime mover drives the rotor at a speed higher than the synchronous speed, it’s similar to pulling on a rubber band: the part that is ahead generates power, that is, the rotor supplies energy to the stator circuit (i.e., the system), and thus the motor is in a generating mode. When the rotating magnetic field of the rotor is slower than the speed of rotation of the stator, it is the stator (the system) that supplies energy to the rotor, thereby driving the load connected to the rotor; this is the electric operation mode.

I also don’t understand the question posed by the original poster. For example, the main fans in large refineries sometimes operate in power-generation mode and sometimes in power-saving mode. Is it true that the electricity generated by the motors in power-generation mode is sent directly to the external power grid? Please, experts, help answer this question.

The large refinery you are referring to is the three-unit setup of flue gas engine-main fan-motor, right? The flue gas extractor recovers the energy from the high-temperature flue gas to generate work; with a constant power output of the main fan, this reduces the load on the motor, thereby achieving energy savings!

What is unclear is whether there is a switching device between the power generation mode and the energy-saving mode; in other words, if it was operating in energy-saving mode during one period of time and started operating in power generation mode at a certain point to supply electricity to the external grid. Does the main fan directly supply electricity to the external grid after drawing power from it? And would such an action have any impact on the external power grid?

No special conversion device is required. The process of absorbing electrical energy from the outside and then transmitting it outward is not instantaneous; there is a progression from positive values to 0 and then to negative values.

Reply to 9# zyz8438: A topic that has caught my great interest recently; I hope experts will share their valuable insights!