In extreme environments like high and low temperatures, the performance parameters of fuses change in the following ways:
High Temperature Environment
Rated Current Reduction
High temperatures increase the resistivity of the fuse material. According to Joule's law (Q=I2Rt), the heat generated increases when the current remains constant. To prevent premature melting due to overheating, the rated current of the fuse decreases. For instance, a fuse with a 10A rated current at normal ambient temperature might only handle around 8A in a high - temperature environment.
Shortened Fusing Time
High temperatures accelerate the heat accumulation within the fuse material. When the current reaches a certain level, the fuse reaches its melting point more rapidly, thus reducing the fusing time. For example, while it may take 10 seconds for a 15A current to blow the fuse at normal temperature, in a high - temperature setting, it could take only 5 seconds.
Accelerated Aging
High temperatures trigger chemical reactions such as oxidation in the fuse's metal material. This leads to a progressive decline in its mechanical and electrical properties, accelerating the aging process. As a result, the fuse is more prone to failure even under normal operating currents.
Low Temperature Environment
Possible Increase in Rated Current
At low temperatures, the resistivity of the fuse material generally decreases. To some extent, this allows a larger current to pass through without generating excessive heat that could cause melting. Consequently, the rated current may increase slightly compared to normal temperature conditions, although this change is relatively minor.
Extended Fusing Time
In low - temperature environments, the fuse material dissipates heat more quickly, slowing down heat accumulation. When an overload or short - circuit current occurs, it takes a longer time for the fuse to reach its melting point. For example, a 20A current that melts the fuse in 3 seconds at normal temperature might take 5 seconds or longer to do so in a low - temperature environment.
Increased Brittleness
Certain fuse materials become brittle and lose toughness at low temperatures. This makes the fuse more susceptible to breakage when exposed to vibrations or impacts, thereby impairing its normal protective function. Additionally, low temperatures can cause the fuse's connection points to contract, increasing contact resistance and potentially leading to local overheating, which also affects the fuse's performance.
