What are the three categories of power transfer limits?

The correct answer identifies the three essential categories of power transfer limits that are pivotal in the operation of electric power systems.

Thermal limits refer to the maximum capacity that electrical equipment, such as transformers and transmission lines, can handle before overheating occurs. If this capacity is exceeded, it can lead to damage not only to the equipment itself but also to the overall reliability of the electrical grid. Managing thermal limits is crucial for ensuring that equipment operates within safe temperature ranges.

Angle stability limits involve the ability of the system to maintain stable power flows under varying conditions. This is particularly important when there are significant changes in load or generation, as these changes can influence the phase angle difference between the voltage at different buses in the system. If the phase angles diverge too much, it can lead to instability or even system collapse.

Voltage limits are critical for maintaining the proper functioning of the power system. Both under-voltage and over-voltage scenarios can severely impact the quality of service provided to customers and can lead to equipment damage. Voltage levels must be controlled to ensure that they remain within specified ranges for the system's reliable operation.

While other options mention elements related to power transfer limits, they miss the specific categorization that is crucial for understanding operational constraints in power systems.