Electrical Power Systems: An Analysis Of The Electric Power System

1.1 BACKGROUND INFORMATION
Modern civilization makes use of large amounts of electrical energy to generate goods and services. This is because, from the industrial manufacturing plants to the providers of public services, all require electrical energy to satisfy and create the well being of modern society as we have today. The essence of electric power systems is to make available, electrical energy for human usage in a very secure, reliable and economic manner. Electric power systems involve the generation, transmission and distribution of electrical energy. Electric power systems are one of the biggest and very complex systems ever built by man, spreading across large geographical area.
The importance of the services that power systems provide

Because power systems operate in different operating voltage levels; different fault scenarios may occur. Protection systems in power systems must provide suitable protection schemes and protective equipment to detect faults and to react to each and every one of these fault scenarios, from the less severe and simple of them to the most complex and compelling (Perez,

With transformers of large capacity, a single transformer fault can cause large interruption to power supplies. If faulted transformer is not isolated quickly, this can cause serious damage and also power system stability problems. Protective systems applied to transformer thus play a vital role in the economics and operation of a power system.
In common with other electrical plants, choice of suitable protection is governed by economic considerations brought more into prominence by the range of size of transformers which is wider than most items of electrical plant. The categories of the power transformers employed in the distribution and transmission levels of the power system range from a few KVA to several hundred MVA.
For transformers of the lower ratings, only the simplest protection such as fuses (J&P fuse) can be justified and for large rating transformers; comprehensive and efficient protection scheme should be applied.
Faults that occur in power transformers are generally classified into four categories:
• Winding and terminal faults.
• Core