Thermal runaway is an uncontrolled positive feedback.

Explanation:
Thermal runaway is a phenomenon that occurs when the temperature of a system increases rapidly due to a positive feedback loop. In this feedback loop, an increase in temperature leads to an increase in some parameter, which in turn further increases the temperature, creating a self-reinforcing cycle. This positive feedback loop is uncontrolled and can lead to catastrophic consequences if not managed properly.

Positive Feedback:
Positive feedback occurs when the output of a system amplifies the input, leading to an increase in the initial disturbance. In the case of thermal runaway, the increase in temperature causes a parameter (such as resistance or current) to increase, which further increases the temperature. This positive feedback loop continues until the system reaches its limit or fails.

Uncontrolled Feedback:
Thermal runaway is considered to be uncontrolled because it occurs without any external intervention or regulation. Once the positive feedback loop is initiated, it continues to amplify itself without any external control. This can lead to a rapid and uncontrollable rise in temperature, which can cause damage to the system or even result in a catastrophic failure.

Consequences of Thermal Runaway:
Thermal runaway can have severe consequences, especially in electrical systems. The rapid increase in temperature can damage components, degrade insulation materials, and even lead to fires or explosions. It is particularly dangerous in high-power systems where the dissipated heat is significant.

Prevention and Control:
To prevent thermal runaway, various measures can be taken. These include the use of thermal protection devices such as thermal fuses or circuit breakers, adequate cooling systems, temperature monitoring, and control algorithms. These measures help in detecting and controlling the temperature rise, preventing thermal runaway and ensuring the safe operation of the system.