Recently, due to concerns about the liberalization of electricity supply, deregulation, and global impact on the environment, securing a reliable power supply has become an important social need worldwide. To ensure this need is fulfilled, detailed investigations and developments are in progress on power distribution systems and the monitoring of apparatus. These are on (1) “digital technology” based on the application of semiconductor high-speed elements, (2) intelligent substations applying IT (information technology), and (3) system configurations aimed at high-speed communication. Incorporated in these are demands for the future intelligent control of substations, protection, monitoring, and communication systems that have advantages in terms of high performance, functional distribution, information-sharing and integrated power distribution management. Today’s conventional apparatus also requires streamlining of functions, improvements in sensor technology, and standardized interfaces. By promoting these developments, the following savings for the whole system can be expected: (1) reduced costs in remote surveillance in the field of apparatus monitoring, operation, and maintenance, (2) reduced maintenance costs based on the integrated management of equipment, and (3) reduced costs due to space saving as a result of miniaturizing equipment.