What are thermal limits directly the result of?

The correct choice highlights that thermal limits are primarily influenced by the thermal capability of system equipment. Thermal limits define the maximum current that equipment, such as transformers and transmission lines, can handle before overheating and potentially failing. This overheating can result from continuous operation at high currents that generate excessive heat due to electrical resistance.

Each piece of equipment is rated for thermal performance, which ensures safe operation under specified conditions. This thermal rating is crucial because exceeding it can result in degradation of the equipment or catastrophic failures, impacting the overall reliability of the power system.

While factors like high torque and power angles or reactive power deficiencies can contribute to system stresses, they do not directly define the thermal limits of equipment. Instead, they may affect how close the system operates to those thermal limits or affect overall system stability and efficiency, but the fundamental thermal limitations arise from the equipment's design and material properties.