If a system disturbance causes a generator to be out of step, what does this mean?

When a generator is said to be "out of step," it refers to a situation where the generator is operating at an asynchronous speed relative to the system frequency. In synchronous machines, generators must maintain a constant rotational speed that is in sync with the electrical grid's frequency. If there is a disturbance—such as a large load change or a fault in the system—the generator may lose synchronization with the grid. This results in the rotor of the generator rotating at a speed that is not aligned with the frequency of the electrical network. This can cause instability and potential damage to both the generator and the power system.

The concept of being out of step is critical because continued operation in this state can lead to further complications, including voltage fluctuations and mechanical stresses. Therefore, recognizing that the generator is at an asynchronous speed helps in diagnosing the issue and taking appropriate corrective actions.