PT PLN (Persero) Salatiga Basecamp Yogyakarta (150 KV Substation Bantul) is a company that contains electrical components that function as managers of the needs of electricity, as well as the safety of equipment that needs electricity in the area of Bantul. Bantul Substation itself has 3 units of power transformers with a capacity of 60 MVA in each power transformer, and operates with a capacity of 16 MW. In the electrical protection system does not close the possibility if there is interference that affects the performance of the equipment used, both inside and outside the equipment, to avoid damage to equipment or things that are not desired. This study aims to determine the quantity of interference and performance of the protection system of the 150 KV Substation in Bantul by using percentage description calculations to obtain data qualitatively. The data generated from the calculation of this percentage description the performance of the relay is said to be good when the calculation gets a minimum of 90%. Based on the results of the research and calculations carried out from 2013 to 2017, there were several criteria for disturbances: technical, non-technical and non-causative disturbances and obtaining a good predicate for each protection system performance at the Substation.