PARAMETRIC IDENTIFICATION OF ARC-SUPPRESSION REACTOR IN THE BASIS OF INSTANTANEOUS VALUES

Single-phase earth faults occur in 6–35 kV distribution networks. One of the devices designed to eliminate earth faults is the arc suppression reactor. The inductance of the reactor is set in resonance with the capacitance of the network, which results in the suppression of the capacitive component of the current. A method of determining the inductance of a reactor using instantaneous values of current and voltage is proposed. A differential equation linking the measured quantities is derived. The equation is written for two moments of time, and a system from which the expression for the reactor inductance is derived. Numerical approximation of the derivatives by means of the asymmetric difference derivative was carried out. The mathematical model of the reactor was composed. The influence of the asymmetry coefficient and the main parameters of the considered transients on the accuracy of determining the reactor inductance was analyzed. The influence of noise on the accuracy of determining the inductance of the reactor was considered. The influence of the main parameters of the considered transients on the stability of the method to noise is analyzed. The confidence intervals of the calculated inductance for different values of relative noise are constructed. An upgraded method for determining the detuning based on the solution of an overdetermined system of equations is proposed. The robustness of the upgraded method to the influence of noise was analyzed. The modernized method has shown to be more robust to the influence of noise in comparison with the method based on solving a system consisting of equations written for two moments of time. A test of the methods on a real oscillogram of current and voltage is described. Recommendations on the practical application of the developed methods are offered. The upgraded method is appropriate when there is a high influence of noise and no limitations on the computing power of devices, the method of calculating the inductance by two readings should be used in all other cases.

Supercapacitance and superinductance of TiN and NbTiN films in the vicinity of superconductor-to-insulator transition

We investigate the low-temperature complex impedance of disordered insulating thin TiN and NbTiN films in the frequency region 400 Hz–1 MHz in close proximity to the superconductor–insulator transition (SIT). The frequency, temperature, and magnetic field dependencies of the real and imaginary parts of the impedance indicate that in full accord with the theoretical predictions and earlier observations, the films acquire self-induced electronic granularity and become effectively random arrays of superconducting granules coupled via Josephson links. Accordingly, the inductive component of the response is due to superconducting droplets, while the capacitive component results from the effective Josephson junctions capacitances. The impedance crosses over from capacitive to inductive behavior as films go across the transition.

MATHEMATICAL SIMULATION OF A DEVICE WITH FREQUENCY OUTPUT FOR MEASUREMENT OF HUMIDITY

The device for measuring humidity with a moisture-sensitive resistive element HR202 has been developed. The self-generating transducer is designed as a hybrid integrated circuit based on a bipolar transistor VT1 and a field-effect two-gate transistor VT2. The negative differential resistance, which is formed by the parallel connection of the impedance with a capacitive component at the collector electrodes of the bipolar transistor VT1, the drain of the field-effect transistor VT2 and inductance L1, leads to the occurrence of electrical oscillations in the circuit. When exposed to moisture on the sensitive resistive element RW, the capacitive component of the impedance at the electrodes of the transistor structure changes, which causes an effective change in the frequency of the oscillatory circuit. On the basis of mathematical modeling of electrical characteristics, analytical expressions for the transformation function and the sensitivity equation are obtained. It has been experimentally established that an increase in the ambient temperature in the range of relative humidity W = 30 ÷ 85% leads to an expansion of the generation range of the autogenerating humidity transducer, as well as to an increase in the sensitivity of the device to the measured value. The generation range of the autogenerating humidity transducer at a temperature of T = 20 °C acquires a value of 823 kHz (the average value of the sensitivity is 16.18 kHz /%), and at a temperature of T = 50 °C – 1323 kHz (the average value of the sensitivity is 29.10 kHz / %). To confirm the theoretical results of circuit solutions developed device in the computer modeling of LTSpice modeling environment. The studies were carried out at different temperatures (20°C, 30°C, 40°C, 50°C) in the range of change in the resistance of the moisture-sensitive resistive element from 1750 kOhm to 2.1 kOhm, which corresponds to an increase in the value of the relative air humidity from 30 % to 90 %. The results of theoretical and experimental studies have shown that at the output there are periodic oscillations device for measuring the humidity rate which increases with increasing values ​​of relative humidity. The obtained theoretical and experimental studies are in good agreement, the relative error does not exceed 2.5%.

MATHEMATICAL SIMULATION OF A DEVICE WITH FREQUENCY OUTPUT FOR MEASUREMENT OF HUMIDITY

The device for measuring humidity with a moisture-sensitive resistive element HR202 has been developed. The self-generating transducer is designed as a hybrid integrated circuit based on a bipolar transistor VT1 and a field-effect two-gate transistor VT2. The negative differential resistance, which is formed by the parallel connection of the impedance with a capacitive component at the collector electrodes of the bipolar transistor VT1, the drain of the field-effect transistor VT2 and inductance L1, leads to the occurrence of electrical oscillations in the circuit. When exposed to moisture on the sensitive resistive element RW, the capacitive component of the impedance at the electrodes of the transistor structure changes, which causes an effective change in the frequency of the oscillatory circuit. On the basis of mathematical modeling of electrical characteristics, analytical expressions for the transformation function and the sensitivity equation are obtained. It has been experimentally established that an increase in the ambient temperature in the range of relative humidity W = 30 ÷ 85% leads to an expansion of the generation range of the autogenerating humidity transducer, as well as to an increase in the sensitivity of the device to the measured value. The generation range of the autogenerating humidity transducer at a temperature of T = 20 °C acquires a value of 823 kHz (the average value of the sensitivity is 16.18 kHz /%), and at a temperature of T = 50 °C – 1323 kHz (the average value of the sensitivity is 29.10 kHz / %). To confirm the theoretical results of circuit solutions developed device in the computer modeling of LTSpice modeling environment. The studies were carried out at different temperatures (20°C, 30°C, 40°C, 50°C) in the range of change in the resistance of the moisture-sensitive resistive element from 1750 kOhm to 2.1 kOhm, which corresponds to an increase in the value of the relative air humidity from 30 % to 90 %. The results of theoretical and experimental studies have shown that at the output there are periodic oscillations device for measuring the humidity rate which increases with increasing values ​​of relative humidity. The obtained theoretical and experimental studies are in good agreement, the relative error does not exceed 2.5%.

Identification of inter-turn insulation faults in induction motor

Purpose Induction motors (IMs) are considered one of the most important elements of the industrial process. However, in this environment, these machines are subject to electrical and mechanical faults, which may cause significant financial losses. Thus, the purpose of this paper is to propose an optimal identification of inter-turn insulation faults present in the random wound IM. Design/methodology/approach The design approach deals with a simple technique, using the effect of the inter-turn fault in modifying the high-frequency components of the applied pulse-width-modulated voltage. Findings The change in insulation strength between the turns affects the capacitive component of the stator line current. Resulting changes in wave shapes of the applied voltage have been studied with respect to both the distance of inter-turn faults from line end and reduction in the insulation strength, and hence in the insulation resistance value. Originality/value Studies have been conducted by using computer simulation and validated by experiments. There is ample evidence that an impending and progressing inter-turn fault can be identified in adjustable speed drives driven by frequency converters by studying line-end coil-voltage waveforms.