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Vol 89, No 8 (2018)
- Year: 2018
- Articles: 12
- URL: https://journals.rcsi.science/1068-3712/issue/view/14323
Article
Characteristics of a Resonant Direct-Voltage Transducer with Phase Control by the Fundamental Harmonics Method
Abstract
Approximate expressions for the calculation of the load and control characteristics of the direct-voltage transducer were obtained by the fundamental harmonics method on the basis of the linear equivalent circuit of a direct-voltage transducer constructed on the assumption of current harmonicity in the series LC circuit. Comparison of the load characteristics constructed according to the grounded exact method based on the fitting method and the obtained approximate formulas shows that the fundamental harmonic method may be used for calculation of the static characteristics at the phase regulation in the continuous current mode with acceptable practical accuracy. In the discontinuous current mode, the method gives an overestimated output voltage, with the exception of the mode close to idling, where the voltage values are underestimated. The error of the basic harmonic method increases with the decrease in the relative duration of the pulses at the output of the inverter bridge.
445-449
Control of the Compensation Mode of the Capacitive Currents of Single-Phase Earth Fault According to the Measured Parameters of a Network Zero-Circuit
Abstract
The control of the compensation mode of the capacitive currents arising in the location of a single-phase earth fault is considered based on the measured parameters of the zero-sequence circuit of the distribution electric network. A brief description of the of the distribution networks with compensation of the capacitive current is given. The drawbacks of the existing methods and automatic adjustment tools of the arc-suppression coils are specified. The necessity of developing a method for determining the parameters of the network zero-sequence circuit without any drawbacks of the known methods of compensation adjustment is substantiated. The method of estimation of the parameters of the network zero-sequence circuit is described. The proposed method is investigated on the basis of circuit models and in the conditions of the existing distribution network. The results of investigations confirm that the proposed method of estimation is viable and has satisfactory metrological characteristics.
450-455
Investigation of the Breaking Capacity of the Automatic Circuit-Breakers in the Short-Circuit Mode
Abstract
Arc-quenching processes in automatic ac circuit breakers with a deionic lattice are considered. It is noted that the arc-quenching system of the circuit-breaker should be functional upon switching of the short-circuit currents, which can exceed 100 kA, and currents from the nominal to critical values of several tens of amperes. One of the main parameters of the arc-quenching system is the number of plates of the arc-quenching lattice, which determines the dimension and the braking capacity of the circuit breaker. The calculation method for the number of gaps ensuring the reliable arc-quenching was proposed. The most optimum design of the arc chute was revealed. Performance of the circuit breakers should be confirmed by the direct switching tests; however, due to the large switching power of the disconnected circuit that is provided for in the regulatory and technical documentation, it is recommended to monitor the operation of the circuit breakers based on the results of preliminary tests in a synthetic circuit.
456-458
Calculation of a Valve Magnetic System of Maximum Current Release of a Circuit Breaker
Abstract
Circuit breakers are one of the most widespread electrical devices in control and distribution systems that use electric energy fluxes, providing protection from short circuits and current overloads. First and foremost, circuit breakers should provide a high operation speed at shutdown, which can be achieved with low weight and significant electromagnetic forces. For approximate determination of magnetic system dimensions, network analysis methods are used. In addition, the model of magnetic field structure can be substantially simplified. The conductivity of air gaps between the ferromagnetic elements of a magnetic system can be described by a modified method of probable paths of magnetic flux, and the resistance of ferromagnetic elements (magnetic potential drop) is taken into account by means of a mathematically expressed magnetization curve (for steel of 10895 grade).
459-463
Calculation of Thermobimetallic Releases of Circuit Breakers with Indirect Heating for Currents from 63 to 250 A
Abstract
Thermal releases based on thermobimetallic elements (TBEs) form the current-dependent part of the protective characteristic of a circuit breaker. The design of a mechanism of free releasing and the characteristics of a thermobimetallic element are analyzed. The operating condition for the thermal release is formulated, which is based on comparison of the mechanical characteristics of an actuator and thermomechanical characteristic of TBEs. Experimental studies of thermobimetallic releases, which are analogues of the breakers to be developed, were carried out. Taking into account the results of these experiments, a design procedure of thermobimetallic release was developed, which is applicable for all types of TBE heating (direct, indirect, combined). The procedure makes it possible to determine the geometrical dimensions of a TBE and the methods of its heating, as well as the operating temperature of release depending on the rated current of the breaker. It has been noted that, to provide the possibility of operating current adjusting, as well as for reliable operation of circuit breakers under vibration and shock conditions, it is necessary to provide for the free running of TBE during design. Comparison of design and experimental data showed the accuracy of procedure, which is acceptable for practical calculations.
464-467
Increasing the Efficiency of the Electrical Drive of an Oil Rocking Machine
Abstract
The issues of energy efficiency of oil-producing rod pump setups with new alternative electric drives on the basis of valve electric engines replacing existing asynchronous motors have been examined. A technique for selecting the main dimensions and a procedure for electromagnetic calculations of the valve motors using commonly applied materials are presented. It has been concluded that, in the drives of oil rocking machines equipped with frequency converters to adjust the speed of oscillations, the use of valve motors instead of asynchronous ones is effective. This should allow reducing the power consumption in the drives of these machines by 10–12%.
468-472
A Design of a Minimized Shell-Type Plunger Constant-Voltage Electromagnet
Abstract
Reducing the weight of the materials used in the creation of electromagnetic devices and decreasing the overall size of the latter greatly increases the attractiveness of low-voltage switchgear such as relays, contactors, and motor starters. These goals can be achieved by forced control of their driving electromagnets and the development of a technique for minimizing weight and size. In this paper, these problems are solved for a shell-type plunger constant-voltage electromagnet used as a drive. For the preferred region of the factor space of the source design data, a computational experiment was performed in accordance with a second-order orthogonal central composite design for eight variables. The polynomial models were developed for an optimal relative proportionality of a working air gap, the winding height and thickness, the outer collar height in fractions of an optimal core diameter, and the stop height in winding fractions. Examples of the calculation of the optimal electromagnet size minimizing its overall volumetric dimensions are given.
473-476
Recording Radiation in the Near-Ultraviolet Range to Determine the Initial Ignition Voltage of Surface Discharge in Air
Abstract
The method of radiation recording in the near-ultraviolet range arising at the surface electric discharge. In the experiment, a double-electrode cell is used in the mode of a power supply by a single rectangular pulse of positive polarity. Using a photoelectric multiplier, a coincidence between the moment of appearance of the discharge current and moment of appearance of the radiation arising at it is specified, which is important for determination of the initial voltage of appearance of the discharge.
477-479
On the Determination of the Initial Ignition Voltage of a Surface Discharge in Air
Abstract
The experimental and calculated values of the initial ignition voltage of a surface barrier discharge in atmospheric air in a plane–parallel electrode system with a Plexiglas barrier are presented. It is shown that the calculation of the initial voltage based on a simplified procedure, in which the criterion of the discharge initiation is the realization of the Townsend condition, provides the calculated dependence of the initial voltage on the barrier thickness, which coincides with the experimental data.
480-483
Artificial Initiation of Lightning in Thunderclouds by Model Hydrometeor Groups
Abstract
Basic provisions of the scientific and engineering fundamentals of the methods of an artificial initiation of the downward lightning and intracloud lightning by the model hydrometeor arrays have been formulated. The key role played by the model hydrometeor size and form on the probability of an artificial initiation of the downward lightning and intracloud lightning has been established. Volume hydrometeors of centimeter size are tailored for such goals. Dividing of the model hydrometeors on the five classes differing on the electric field amplification coefficient has been proposed. Model hydrometeors with the amplification coefficient from 5 to 19 will be the most optimal for an artificial lightning initiation. It was found that the requirements for the sizes and parameters of the model hydrometeor families and to the places of their introduction in a thundercloud will be determined in most by the effect of the earlier appearance of the avalanche corona on the hydrometeors. It discharges the nearest parts of the thunderstorm cells leading to the local decreasing of the field strength, probability of the streamer corona initiation, and its transition into the volume leader. It was determined that the combining of the model hydrometeors in the group by the dielectric string or tape and the simultaneous introduction in thundercloud of some hydrometeor arrays will significantly increase the probability of the artificial initiation of the intracloud lightning and lightning “cloud–ground,” and the successful discharging of a thundercloud. Moreover, the minimal linear sizes of separate hydrometeor groups should be more than several dozens of centimeters. Some variants of the disposition of the model hydrometeor groups in a thundercloud (near the bottom boundary of the thunderstorm cell, inside the thunderstorm cell, and in the space between the thunderstorm cells) when the most optimal conditions for the initiation of the intracloud lightning and lightning “cloud—ground” are provided, have been proposed.
484-489
Resonance Overvoltages in Primary Winding of a Station Service Voltage Transformer
Abstract
The design of new types of transformer equipment, in particular, station service voltage transformers (SSVTs), requires a detailed consideration of all technical aspects and conditions of their application and their design features. One problem is to provide their resistance to effects associated with their interaction with the grid. During transient events in the network caused by the operation of switching equipment or short circuits, the transformers are affected by the oscillating voltage, which, under certain conditions, can cause resonance overvoltages inside their windings. The design of SSVTs differs from that of common power transformers, mostly because different types of windings are used, which determines the essential difference in the natural oscillation frequencies and the theoretical possibility of the development of resonance overvoltages under changed combinations of network parameters and switching conditions. In this paper, the problems of estimating the natural and dominating oscillation frequencies in SSVT windings and the voltages on the longitudinal insulation of SSVT windings under the resonance conditions are considered. The proposed approach is applicable not only to SSVTs, but also to other types of transformer equipment.
490-495
Force Interaction in Magnetic Systems with a Volumetric High-Temperature Superconductor
Abstract
The paper presents the results of the theoretical and experimental studies of force interactions between permanent magnets and volumetric high-temperature superconductors (HTCs). The obtained data are of interest for the design of various devices with HTC elements: magnetic bearings, transport systems with magnetic levitation, electric machines, etc. Numerical analysis of the electromagnetic field was performed by the method of spatial integral equations for the field sources. The properties of the HTC materials and YBaCuO ceramics are represented by a traditional model for transport currents and a combined model that considers the types of field sources inside the superconductor—the transport current density and the related currents (magnetization). For the transport current density, a modification of the critical state model is applied. In this model, the specific electric resistance of the superconductor is presented by a hyperbolic function of the following three parameters: absolute temperature, magnetic field strength, and current density. The model for magnetization is based on the definition of the related currents in the form of the density of the magnetic moments’ combination of the small superconducting cylinders throughout the sample of a high-temperature superconductor. Experimental studies were performed on a specially designed installations with the HТС cryostatting system in a liquid-nitrogen atmosphere and equipment for precision force sensing. Comparison of the experimental results and calculation data confirms the reliability of the developed modeling methods.
496-500