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eARth fAult PRoteCtIoN foR CoMPeNSAteD eleCtRIC NetwoRKSBASeD oN fRequeNCy fIlteRS Purpose. Development of selective microprocessing earth fault protection in compensated electrical networks of 6-35 kV. Use of the Goertzel algorithm for the separation of components of frequencies higher than fundamental frequency from the zero se quence voltage and currents.Methodology. The methods of mathematical modeling and analysis of transients in compensated electric networks of 6-35 kV, Fourier transform and Goertzel algorithm, construction of earthfault protection algorithms, and experimental research are used.findings. The results of mathematical modeling show that in compensated electric networks of 6-35 kV at phasetoground fault the reactive power direction in a in a damaged feeder1can be similar to the one in an undamaged feeder1; therefore, conven tional protections cannot perform selective operation. This action can be provided by protections based on separation of compo nents of fixed frequencies of 200-300 Hz from the zero sequence voltage and currents. Their reactive power in an undamaged connection is always directed off tyres, because is hardly compensated by the reactor regardless of degree of its cavity tuning. When applying bandpass frequency filters, the required protection responsivity is not always provided at phasetoground fault through resistances exceeding 10-15 Ohm. Moreover, failure of steady operation of filters is possible due to location of their poles on a circular curve of a unit radius, while use of blocks of numerical differentiation of current and voltage can result in running failure at alternate arcing ground. The application of the Goertzel algorithm for highfrequency components detection is proposed. It is implemented through an infinite impulseresponse filter of the second order with two real coefficients in back coupling and one complex coefficient in circuit of direct relation. The results of simulation of the behavior of protection in the system of computer algebra Mathcad confirmed the reduction of calculation costs and stable work, regardless of the presence of aperiodic components at different initial phases of the voltage at the time of fault. As part of the protection, a trigger unit is provided that allows the op eration if the voltage of the zero sequence exceeds the setpoint, which is 12-15 % of the nominal value. In order to ensure reliable operation of the protection, permanent and arcing faults provide activation of protection impulses in the event of a fault. The positive results of protection algorithm were achieved on the mathematical model of the network as well as when testing a micro processor prototype of a protective system in a laboratory environment. originality. For the first time for groundfault protection in 6-35 kV compensated networks, it is proposed to separate compo nents of frequencies higher than fundamental frequency from the zero sequence voltage and currents using frequency filters cre ated on the basis of the Goertzel algorithm are proposed; the algor...

Introduction. A significant proportion of earth faults in 6-35 kV networks is a transient and short-lived process, which is followed by an electric arc. Problem. In such cases, earth-fault protection that responds to steady-state current and voltage is not able to operate properly. Also, the use of the Petersen coil to compensate for the capacitive earth fault current complicates the protection function because it significantly reduces the single phase earth fault current in steady state. Purpose. To develop selective single-phase earth faults protection algorithm using harmonic components that occur in zero-sequence currents and voltage in the transient process. Method. A mathematical model of the power supply system is applied to study the frequency components of currents and voltage of zero sequence in compensated electrical networks with phase-to-earth faults, and a mathematical model is used to test the operation of the developed protection algorithm. The results showed that, the reactive power for harmonic components of the frequency greater than 100 Hz, which are separated from the current and voltage of zero sequence in compensated electrical networks on the damaged feeder, is positive regardless of the degree of compensation of the capacitive current. That may be the basis of the principle of directional protection. Originality. Phase-to-earth fault selective protection algorithm has been developed. In that algorithm, first derivatives of currents and voltages of zero sequence are found, to reduce the influence of aperiodic components. And then, by using of the Fourier transform, a number of harmonic orthogonal components are extracted from them. Reactive power is calculated for each of frequency component and their total sum is found. If that sum excess of threshold, the relay will make a decision. The reliability of the developed protection algorithm is confirmed by the results of mathematical modeling and verification of the test sample at the laboratory stand and by means of field signals that were recorded by digital loggers at the substations. References 10, table 1, figures 6.

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The purpose of the article is to improve the single-phase earth fault protection for compensated electrical networks by eliminating the disadvantages of the known protection methods. The developed mathematical model revealed the possibility of non-selective protection operation due to the influence of aperiodic components in currents and voltages in transients. Insufficient sensitivity of protection at phase to earth faults due to active resistors greater than 10-20 ohms was also detected. The dependence of the reactive power on the frequency of the signals, isolated by the Hoertzel filters was obtained. These filters are taken as a basis because they require less computational cost than a discrete Fourier transform. It is suggested to perform differentiation before applying current and voltage of zero sequence to the frequency filters, which reduces the influence of aperiodic components on the phase errors of the relay and greatly enhances the useful signals. To increase the sensitivity of the relay when the phase is grounded through active resistance up to 100 Ohms, the relay circuit includes Hoertzel filters (for current and voltage) to select the components for two different frequencies (both higher than fundamental), and reactive power is found as the sum of power for the first and second frequencies. The sensitivity of enhanced protection algorithms compared to known algorithms is increased 10-20 times. References 13, figures 6, tables 2.1 / 3 2020 n5 s11