The methods used in the microprocessor protection of electrical equipment for forming orthogonal components of input currents ensure their reliable isolation after changing the mode followed by one or more periods of the fundamental frequency. This is due to the inertia of the functional elements, in particular, digital frequency filters, as well as the saturation of the steel magnetic cores of current transformers. To increase the speed of the selection of orthogonal components of the input currents, it is proposed to form them as equivalent ones in terms of the cosine and sine components obtained using digital Fourier filters by multiplying by the resulting coefficient. The method that has been developed for determining the specified coefficient provides compensation for the delay caused by the inertia of digital filters, as well as the saturation of the steel of magnetic cores of current transformers. The proposed method of forming orthogonal components is highly effective in the modes of strong saturation of the magnetic core with a complex input action in the presence of an aperiodic component with a large damping time constant. The evaluation of the efficiency of the proposed method was performed using a complex digital model implemented in the dynamic modeling environment MatLab-Simulink. As a result of the performed studies, it was found that in the absence of saturation of the magnetic core of current transformers, as well as in the presence of a small and medium degree of saturation, the proposed method for forming equivalent orthogonal components of input currents has dynamic properties close to the ones of those that had been previously proposed. With a strong saturation of the magnetic core of current transformers, the speed of obtaining reliable values of these components is increased by 1.5–2 times.

Recently, there has been an increased interest in the use of artificial neural networks in various branches of the electric power industry including relay protection. The operation of the traditional microprocessor-based relay protection device is based on calculation the RMS values of the monitored current and voltage signals and its comparison with the predetermined thresholds. However, calculated RMS values often do not reflect the real processes occurring in the electrical equipment under protection due to, for example, current transformer saturation. In this case secondary current has a characteristic distorted waveform, which is significantly differs from its ideal (true) waveform. This causes underestimation of the calculated RMS value of the secondary current compared to its true value; also, it causes a trip time delay or even to a relay protection devices operation failure. In this regard, one of the perspective applications of the artificial neural network for the relay protection purposes is the current transformer distorted secondary current waveform restoration due to its saturation. The article describes in detail the stages of the practical implementation of the artificial neural networks in the MATLAB-Simulink environment by the example of its use to reconstruct the distorted secondary current waveform of the saturated current transformer. The functioning of the developed neural networks was verified in the MATLAB-Simulink environment; with the use of the SimPowerSystems component library a model was implemented which allow simulating the current transformer saturation, accompanied by the secondary current waveform distortion, and its further restoration using developed artificial neural networks. The obtained results confirmed the ability of the neural networks that had been developed to almost completely restore the distorted secondary current waveform. Thus, it seems promising to use pre-trained artificial neural networks in real relay protection devices, since such use will ensure the speed of real relay protection devices; their operation reliability will also increase.

In the measuring elements of the current of microprocessor protection, the controlled values are usually the effective values of the fundamental harmonic of the currents. They are determined by the orthogonal components of the input signals, which are formed by digital Fourier filters. Due to the inertia of these filters, the time for obtaining reliable effective values is one or more periods of the input current, which mainly determines the speed of the measuring element. When the frequency of the input signal deviates from the nominal value, its effective values become oscillatory. As a result of this, unstable functioning of the specified organ may occur at current values that are close to the operation and return areas. To increase the speed of the measuring body, it is proposed to determine the effective value of the current by multiplying its value obtained using the orthogonal Fourier components by a correction factor. To ensure the stable functioning of the current organ, it is recommended to filter the effective current value using a digital moving average filter. Evaluation of the effectiveness of the proposed solutions has been carried out by the method of computational experiment using thedynamic simulation environment MATLAB-Simulink. The proposed solutions provide an increase in the speed of the current measuring organs and their stable operation when the frequency deviates from the nominal. As a result of the research, it has been found that the proposed digital current measuring organ in comparison with an organ based on the Fourier algorithm has a speed of 1.4-2 times greater. In addition, it functions stably both under the condition when the tripping current is less than the fault current, and in the case when the indicated currents are comparable when the frequency deviates from the nominal by ±2 Hz. The proposed digital measuring body can be used in many microprocessor-based current protection of electric installations.

The use of orthogonal components (OC) underlies  the construction of measuring elements of  modern protection and automation devices. In most microprocessor-based protections, the orthogonal component of the input signal is extracted using a discrete Fourier transform (DFT). The DFT disadvantages are its low speed, which is more than one period of the fundamental frequency, as well as the sensitivity to the free aperiodic component, which creates significant conversion errors depending on the time constant of its decay. Such a settling time of the true output signal is often unacceptable for the design of high-speed measuring devices. The paper proposes to form the OC of the equivalent signal according to the values of the cosine and sine OC of the fundamental harmonic, formed using the DFT by multiplying them by the resulting correction factor. The developed algorithm for the formation of orthogonal components of input signals in microprocessor protections is characterized by high speed in transient modes and it has wide functionality. So, the proposed digital device for forming the orthogonal components of an equivalent signal, in comparison with digital filter based on the DFT, has an increased operating speed both in the mode of occurrence of a short circuit and during the decay of the monitored signal, while maintaining the same characteristics as in the DFT in other modes. A block diagram of the proposed digital device for forming the OC of an equivalent signal has been developed, all blocks of which can be implemented on a microelectronic and microprocessor element base. A digital model of the specified device has been developed in the dynamic modeling system MatLab-Simulink in accordance with the structural diagram. As a result of the calculations, a significant (up to two times) increase in the performance of the proposed digital device for forming the OC in transient modes has been established in comparison with the shapers based on the DFT.

This article presents the implementation of digital filters used in microprocessor-based (digital) relay protection current measuring elements. It has been shown that in order to reliable estimate the digital filter performance its input signals waveforms must be close to the actual secondary current waveform of the current transformer (CT) to which the digital protection with the estimated digital filter is connected. Ways of digital filtering improvement based on the window functions usage are proposed. Streszczenie. W pracy przedstawiono przykład wdrożenia filtrów cyfrowych stosowanych w elementach pomiarowych zabezpieczenia przekażnika prądowego na bazie mikroprocesora cyfrowego. Wykazano, że w celu wiarygodnego oszacowania wydajności filtrów cyfrowych ich przebiegi sygnałów wejściowych powinny być zbliżone do rzeczywistego przebiegu prądu wtórnego transformatora prądowego do którego jest podłączono zabezpieczenie cyfrowe z pomiarowym filtrem cyfrowym. Zaproponowano sposoby poprawy filtracji cyfrowej w oparciu o wykorzystanie funkcji okna. (Ocena porównawcza filtrów cyfrowych stosowanych w mikroprocesorowym zabezpieczeniu przekaźnika).