Protection system faults 1999 – 2003 and the influence on the reliability of supply

Protection and control systems play important roles in power system operation and for the reliability and security of supply. This paper presents main results from a study of incorrect operations of protection and control systems on the voltage levels 1 - 420 kV in Norway, comprising mainly false and missing operations. The statistics for the period 1999 - 2003 show that false or unwanted operation is the major fault type and that the relative number of faults and the contribution to energy not supplied (ENS) increase by increasing voltage level. Incorrect operations of protection and control systems at the transmission levels 33 - 420 kV contribute to 34 % of the total number of power system faults and 17 % of ENOL at these levels. Human related causes dominate by roughly 40-50 %, technical causes count for 20-30 %, while there are large portions of faults where the cause is not identified.