Microprocessor Selective Protection From the Phase to the Earth Fault in Electric Networks With Petersen Coil in Neutral

Elektroteh. elektromeh.

2020

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.

Section: с помощью математической модели компенсированной электрическmentioning

confidence: 99%

Section: с помощью математической модели компенсированной электрическmentioning

confidence: 99%

Мultifrequency Protecting Method Against Earth-Faults of Phase in the Compensated Electric Networks

Elektroteh. elektromeh.

2020

“…For this reason, active research on transient processes and the development of protection methods using WT algorithms are still ongoing, and the search for the optimal base (kernel, mother) WT function is underway [17,18]. The selection of frequency components can be carried out using both WT and classical digital filters [19,20]. Numerous attempts have been made to use various methods based on artificial neural networks (ANNs) to protect against singlephase-to-ground faults, however, in our opinion, the possibilities of simpler approaches have not been exhausted, among which the most attractive is the analysis and use of components of different frequencies in currents 3i0 and voltages 3u0 of zero phase sequence.…”

mentioning

confidence: 99%

Application of Wavelet Transform for Phase-to-Ground Fault Protection in Medium Voltage Electrical Networks

2021

Teh. elektrodin.

Self Cite

For electrical networks with voltage of 6-35 kV with a compensated, isolated or resistor-grounded neutral, a phase-to-ground protection has been developed, in which, based on the results of the time-frequency wavelet transform of zero-sequence currents, voltages and their derivatives, using the obtained analytical expression, the total reactive power wavelet for different frequencies is determined. It is shown that at the initial moment of a phase-to-ground fault on the damaged feeder the power is always positive, and on the undamaged feeder it is negative, regardless of the operating mode of the neutral. Wavelet transform coefficients are found by convolution of discrete values of measured signals with sine-cosine signals of the Morlet mother function. The time-reversed sequence of these signals is obtained using a matrix for which the rules for its formation are stated. An excess of the zero phase sequence voltage amplitude of the set value is used as a starting protection element. With the help of a mathematical model of the network, studies of the behavior of protection in case of blind and arc phase-to-ground faults at various degrees of compensation of capacitive currents, at various voltage values at the moment of the short circuit have been carried out. In all modes, a reliable protection operation is obtained, the sensitivity of which is an order of magnitude higher than the protection based on Fourier transforms. Positive results of testing a protection sample implemented on a microprocessor-based element base at a laboratory stand are obtained. References 20, figures 7, tables 2.

“…Despite the shortcomings in [9] regarding the choice of the bandpass filter parameters and the construction of pro tection algorithms, this approach turned out to be very prom ising. In [10], it was proposed to improve such protection by performing it twochannel, more stable and sensitive due to the use of filters with improved characteristics and differentia tion units for currents and voltages in order to obtain their or thogonal components. The disadvantage of this protection is the lack of sensitivity during earth faults through resistances of more than 10-15 ohms.…”

mentioning

confidence: 99%

“…1. The mathematical model is described in [10] and consists of differential equations for branches and nodes of the circuit and earth fault protection algorithms. To increase the numerical stability of the model in it, the solution of dif ferential equations is performed by implicit integration me thods.…”

mentioning

confidence: 99%

Earth fault protection for compensated electric networks based on frequency filters

Nauk. visn. nat. hirn. univ.

2020

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...