How is the steady state stability related with the air gap density?

The steady state stability of an electric machine, such as a synchronous generator or motor, is closely connected to the air gap power density, which is a measure of the magnetic flux density in the air gap between the stator and the rotor. The air gap flux density significantly influences the machine’s capacity to maintain synchronous operation under steady-state conditions.

Here’s a more detailed explanation:

1. Air Gap Density and Torque Production: The air gap magnetic flux density directly affects the amount of electromagnetic torque a machine can generate. Higher air gap flux densities enable the machine to produce more torque. This is crucial in maintaining the synchronous speed under varying load conditions, which is a fundamental aspect of steady state stability.

2. Saturation and Stability: As the air gap flux density increases (due to an increase in current, for example), the magnetic materials in the motor or generator can approach saturation. When saturation occurs, small increases in current will not result in proportional increases in flux density. This can affect the machine’s capability to respond to additional load without falling out of synchronization, thereby impacting steady state stability.

3. Heating and Efficiency: High air gap density can lead to increased losses due to hysteresis and eddy currents in the magnetic materials. These losses convert to heat, affecting the machine’s efficiency and, potentially, its stability, as overheating can alter material properties and lead to derating.

4. Excitation Control: In synchronous machines, the excitation system controls the