Over Current & Power System Protection

•Electrical power systems must be designed to serve  a variety of loads safely and reliably. Effective  control of short-circuit current, or fault current as  it is commonly called, is a major consideration  when designing coordinated power system protection. 

•In order to fully understand the nature of fault  current as it is applied to electrical power system  design, it is necessary to make distinctions among  the various types of current available, normal as  well as abnormal.

•It is also important to  differentiate between the paths which the various  types of current will take

•Both current type and  current path, as well as current magnitude, will  affect the selection and application of over current  protective devices .