Design of a Time Synchronization System Based on GPS and IEEE 1588 for Transmission Substations

Accurate timing is often required for the intelligent electronic devices (IEDs) used in transmission substations. A common method of achieving this is direct connection of a device to a local global positioning system (GPS) receiver and the use of its one-pulse-per-second synchronizing signal and the IRIG-B coded message. However, concerns about GPS reliability are encouraging the use of timing systems less dependent on the direct use of local GPS receivers. The IEEE 1588 protocol is a network-based time synchronization technique designed to coexist with IEC 61850 applications and deliver sub microsecond timing accuracy. Many utilities are now considering the adoption of IEEE 1588, but they need confidence in the reliability of this technology before it can be rolled out to real substations. Hence, comprehensive tests were undertaken on an IEEE 1588 timing system, to help gain insight into the limitations of the system. This paper presents a procedure to assess the performance of a timing system based on distributed GPS receivers and one based on a mixture of GPS receivers and IEEE 1588 devices. Test results indicate whichever system is selected, high quality devices and systems, with appropriate installation and engineering, are essential to satisfy the stringent +/- 1 mu s accuracy requirements needed by critical IED applications.