Which description best captures the factors contributing to thermal runaway in a nickel-cadmium battery installed on an aircraft?

Which description best captures the factors contributing to thermal runaway in a nickel-cadmium battery installed on an aircraft?

• A. High internal resistance with low temperatures
• B. Moderate current with a current-limited charging system
• C. No relation between temperature and charging current
• D. Low internal resistance intensified by high cell temperatures and a high current discharge/charge rate in a constant potential charging system

Answer: (D)

Thermal runaway happens when the heat produced inside a cell exceeds the heat that can be removed, creating a self-reinforcing rise in temperature. In a nickel-cadmium battery on an aircraft, heat comes mainly from I^2R losses and exothermic charging reactions. If the cell temperature climbs, the internal resistance tends to drop, and under a constant potential charging system this lower resistance allows a higher current to flow. A high discharge/charge rate means more current is available, so even with low resistance the power being generated (and thus heat) can be substantial. If cooling is limited in the aircraft environment, that heat isn’t removed quickly enough, so the temperature keeps rising, resistance drops further, current increases, and a dangerous feedback loop begins. The described combination—low internal resistance enhanced by high temperatures and a high current in a constant-potential charging setup—best captures this self-accelerating process.

Thermal runaway happens when the heat produced inside a cell exceeds the heat that can be removed, creating a self-reinforcing rise in temperature. In a nickel-cadmium battery on an aircraft, heat comes mainly from I^2R losses and exothermic charging reactions. If the cell temperature climbs, the internal resistance tends to drop, and under a constant potential charging system this lower resistance allows a higher current to flow. A high discharge/charge rate means more current is available, so even with low resistance the power being generated (and thus heat) can be substantial. If cooling is limited in the aircraft environment, that heat isn’t removed quickly enough, so the temperature keeps rising, resistance drops further, current increases, and a dangerous feedback loop begins. The described combination—low internal resistance enhanced by high temperatures and a high current in a constant-potential charging setup—best captures this self-accelerating process.