Explain the importance of fault current calculation in power system anlysis?

Answer 1

Available fault current, or short circuit calculations, are used to determine ratings of some equipment such as breakers, circuit switchers, etc. Also, short circuit calculations are used to set protective equipment that protects the electric system from adverse events (lightning strikes, tornadoes, earthquakes, people ramming cars into power lines, etc.)

There are other reasons, but the above is the #1.