Evaluation of Electric Signal Frequency Based on Binary and Continuous Wavelet-Transform

Abstract

The calculated values of electric signal frequency are the result of digital processing; they are used for obtaining modules and angles of current and voltage phasors. Such phasors are used in protection and automation algorithms that operate close to real time conditions. Reduction of the frequency estimation error and the time of obtaining its valid value improves the time of application control algorithm response to changes in the operating mode, the control action accuracy and reduces the plausibility of their false operation. The article considers application of binary and continuous forms of the wavelet transform for the electric signal analysis aimed for obtaining the calculated values of instantaneous and levelled synchronous frequency. In a synthetic mode with the stepwise frequency change and the use of disturbance recordings made by real devices and containing the out-of-step, low-frequency oscillations and the short-circuit mode, the advantages of wavelet application for frequency estimation compared with the algorithms that are used in phasor measurement units. Integration of the developed wavelet-transform-based frequency calculation algorithms into the existing hardware of microprocessor-based relay protection and automation, and the recorders of transient process monitoring system, with consideration of the mentioned advantages and disadvantages helps to reduce the error of frequency estimation and to improve the control algorithm operation efficiency.