Precise measurement of power system frequency and absolute phase based on GPS

A precise calculation method of absolute phase angles and stable power frequency is presented in this paper. Firstly, the absolute phase angle of positive sequence voltages/currents relative to 1 PPS (1 pulse per second) from GPS is calculated by using discrete Fourier transforms (DFT). Then a most direct precise measurement of power frequency excursion Δf is proposed by using the absolute phase angles every 1 PPS directly. The main point of the algorithm is that the sampling number of 1 period of fundamental signal can be considered as the reciprocal of nominal frequency for the phase angle-1PPS. The method here not only obtains high accurate frequency and absolute phase angles of entire power systems, but also reduces or eliminates the clock errors caused by crystal oscillators and inconsistency of electric components. So it is very cost-efficient and easy for engineering applications. The experimental results demonstrate the high accuracy of the algorithms. The measurement unit we designed sends measured phase angles and frequency to SCADA systems through the industrial Ethernet per second. This information of the entire power systems can be used for state estimation, prediction of instability and adaptive relaying.