Limitation of interruptions in service of MV distribution systems by improvement of lines insulation and fast localising of earth fault

The overall length of medium voltage (MV) lines, both cable and overhead, exploited by polish distribution companies was 234 827 km at the end of 2003. Every year the percentage share of cables in electrical power network is increasing. Very similar situation can be observed for insulated or covered overhead lines, which are an alternative to bare conductor lines. The evaluation of reliability of MV lines has been established on the basis of service experience obtained from the Utilities. The analysis clearly shows gradual limitation of discontinuous delivery of electricity thanks to, amongst other reasons, more widespread use of overhead-insulated lines.