The purpose of the thesis was to implement a 1-phase high speed automatic reclosing with a Siemens 7VK87 autoreclosing relay in a 400 kV double bus double breaker system. The intention was also to implement standard solutions for the relays I/O signals, the test program and the necessary documents for 1-phase high speed automatic reclosing. The thesis was commissioned by Fingrid Oyj. The thesis deals with the structure of power transmission networks, the most common fault locations, 400 kV line protection and autoreclosings. The thesis began with design based on the implementation of a 3-phase high speed automatic reclosing and previous 1-phase autoreclosing implementations. A test circuit was made with a relay tester and a circuit breaker simulator for functional testing. The aims were successfully achieved, which will facilitate future projects. The thesis defined unambiguous solutions for the implementation, which reduce the workload in the implementations of equipment from other manufacturers and facilitate quality assurance in projects.