Frequency Estimation in Modern Protection Relays

Abstract

This thesis had two goals, first to provide an evaluation scale and simulation framework usable for power grid frequency estimation method simulation and secondly to provide test results of the most promising methods using these tools. The test method developed with Matlab was to be non-hardware dependent to avoid biasing of the test results in favor of any specific hardware platform.

The theory behind two commonly used methods DFT and zero crossing and also three newer ones SDFT, spectrum amplitude comparison and trigonometric method was presented. Three of these five methods SDFT, spectrum amplitude comparison and trigonometric method were chosen for further testing by simulations using the developed test method.

The theoretical evaluation included start-up time, computation window length, estimation rate, computational complexity, fixed-point suitability and functional frequency range. Areas covered by the simulations were harmonics, transients, under voltage, alternative sampling speed, frequency derivative and signal noise. All evaluations were made in a one to ten scale for every separate test. A weighted summary grade was made for every frequency estimation method.

Two of the simulated methods SDFT and spectrum amplitude comparison showed to be promising candidates for further testing in actual protection hardware.