Can a synchronous machine have a negative torque angle, and what does it indicate?

A synchronous machine can indeed have a negative torque angle, and this condition has specific implications. When we discuss torque angle in relation to synchronous machines, we are referring to the angle between the rotor's magnetic field and the stator's magnetic field. A negative torque angle signifies that the rotor is lagging behind the stator magnetic field.

In practical terms, when a synchronous machine operates with a negative torque angle, it indicates that the machine is absorbing active power. This typically occurs when the machine is functioning as a load rather than a generator. In this mode, the rotor cannot keep up with the rotating magnetic field, resulting in a situation where the machine draws power from the grid, thereby acting like a motor.

This behavior is crucial for understanding the operation of synchronous machines in power systems, especially during various operational states. It highlights dynamic interactions that occur when machines switch from generating power to consuming it, and is essential for grid reliability and stability analysis.