The bus size of confluence aluminum in a substation is 63mm-8mm, the skin effect coefficient Ks-1.03. Under normal operation, the temperature of bus is 0-50C ,and cutting time of short circuit is tk-2.6s, short circuit I" 15.8KA, I1.3=13.9kA, I2.6-12.5kA. The equivalent time of the aperiodic component is 0.05s. (Note: In case of short circuit operation, The allowable tempurature of hard aluminum can be 200C) (1) Why to do short-term heating calculation? (3points) (2) When selecting a disconnector, do you need to select or check it according to the rated breaking current? And why? (6 points)