The outage cost was estimated in a variety of ways since the first began use in utility planning about 20 years ago. In addition, the information of outage frequency and the outage duration tended to use increasingly with the outage cost for optimizing investment cost of power system reliability improvement [1].However, the outage cost of industrial customers depends on several factors. For instance, the process characteristic, size of industry, machines and equipment of each industrial type are different especially in large industrial customers. Therefore, the outage cost of each industrial type is affected in the investment cost of utility planning [2].