Fault rates of different types of medium voltage power lines in different environments

Society is increasingly dependent on continuous power supply. This is also taken into account in regulation models, where, in Finland, the customer´s interruption costs CIC now directly affect the profit allowed for distribution system operators. This has led to the situation, where the CIC directly affects the network planning, including decisions on line types and line routing. Hence, more information is needed for detail planning, about the fault rates of different line types and how these depend on line routing, i.e. line location and surroundings. This paper gives a summary about what is known of fault rates, both in the case of short interruptions (fast and delayed reclosing) and long interruptions (permanent faults). The paper is based partly on fault statistics collected by Finnish Energy Industries and some power companies, partly on analytical studies. The core of the paper is the comparison of bare conductor overhead lines, covered conductor overhead lines, underground cables and air cables, located in forests, along the roads or in open spaces.