Walsh transform based digital protection of power transformer

The problem of protection of power transformers against abnormal conditions such as faults etc. has been of great concern to the protection engineers. Traditionally, percentage differential relaying scheme has been used to protect the transformer against internal faults, even though this relaying scheme may mal operate due to various reasons such as magnetizing and overvoltage inrush currents. The proposed relaying scheme incorporates the magnetizing inrush current as well as overvoltage inrush phenomena due to switching for the purposes of blocking only. The fundamental, second-harmonic component caused by magnetizing inrush current and the fifth harmonic current caused by voltage inrush have been realised using digital filter based Walsh transform because of its immunity to slight frequency variations and also because of accuracy. The relaying scheme which uses the concept of unit protection has been designed, fabricated and tested using 8086 CPU as the main processor.