Research On The Precise Calculation Of Power Frequency And Vector

Frequency is a very important quality in power system. It can show the dynamicenergy balance. The Smart Disctete Fourier Transforms (SDFT) has been improved inthis paper after analyzing it in rigorous mathematical deducing. The improvementsinclude three aspects: amending formula, smoothing datas, and adding threshold value.The improved SDFT can calculate more accurately and the data curve becomessmoother. Simulations prove that the improved SDFT can calculate accurate powerfrequency when the system is in normal condition and can track system frequencywhen power frequency deviates from 50HZ.In protection relay, vector's measuring accuracy decides the protection relayequipment'action. Nowadays, Disctete Fourier Transforms (DFT) is widely adoptedto calculate vector's amplitude and phasor in computer protection installation. ButDFT can't get accurate vector's amplitude and phasor when faults happening andfrequency deviating in power system. With the development of Digital SignalProcessing (DSP), it becomes possible for computer protection to calculate accuratefrequency. Some possible problems of SDFT have been analyzed, and SDFT has beenpromoted again. We call the improved SDFT as Improved SDFT (ISDFT). Wesimulate various current faults, oscillations, oscillation and faults by ATP to checkISDFT's accuracy. The simulation results prove that ISDFT can remove DC offset andharmonics' influence, and calculate power current/voltage's amplitude and phasor.And what is more important is that the calculation results are more accurate and closerto real value than DFT.Moreover, the ISDFT is easy to realize. It will very suitable for use in real time.We can get a conclusion that it has a good applicable future in engineering.