


Том 87, № 7 (2016)
- Год: 2016
- Статей: 11
- URL: https://bakhtiniada.ru/1068-3712/issue/view/14198
Article
Identification of the parameters of distribution networks by synchronized current and voltage measurements
Аннотация
On the basis of synchronized measurements of current and voltage phasors, a technique for identification of parameters of 0.4- and 6- to 10-kV lines is suggested. The technique is based on the methods of statistical processing of sets of network modes and composed of several steps. The first step is acquisition of statistical data on network modes. It involves periodic measurements of synchronized current and voltage phasors at injection nodes. The second step is direct statistical processing of the obtained information using the method of least squares. The technique was tested using a three–phase physical model of a network. The mean error of identification of resistance and reactance was approximately 0.5 and 1%, respectively.



Identification of parameters of models of electric network elements on the basis of Tellegen’s theorem
Аннотация
An evaluation criterion of the permissibility of using the parameters of a model to identify modes of electric network elements with consideration for the constancy of parameters being identified and the error of results based on Tellegen’s theorem is presented. Calculating formulas of proposed criterion for various elements of an electric power system are developed. The proposed criterion makes it possible to detect the presence of distorted information and evaluate the identification error.



Parameter determination of a nonsinusoidal periodic signal harmonic based on the modified sine transform
Аннотация
An algorithm is presented for determining the amplitude and the initial phase of the oscillations of the kth harmonic included in the structure of the nonsinusoidal periodic signal. The algorithm differs from the well-known Euler–Fourier method based on sine and cosine transforms. The qualitative difference of the proposed method consists in the use of the cosine function, which is an analytic solution of a modified sine transform, the structure of which includes a sinusoidal factor with a complex argument that contains a variable phase angle. The coordinates of the maximum of this functional dependence, which is raised to a positive integer power to improve the accuracy of determining the parameters, are uniquely associated with the amplitude and the initial phase of oscillations of the kth harmonic of the nonsinusoidal signal. The considered method minimizes the use of nonlinear operations and at its core has the element inherent in the selective filter. The possibility of obtaining information on the parameters of the first voltage and current harmonics with the required accuracy enhances the reliability of the evaluation of processes occurring in the power system in the conditions of interference in the form of higher harmonics. An example problem is solved in the MS Excel environment.



Glaze ice melting on overhead power lines with controllable rectifying installations
Аннотация
General information on controllable rectifying installations that are used in Russia and abroad for melting of glaze ice on overhead power lines (OHLs) involving shutdown is given. There are two types of ice melting plants (IMPs): with pulse-phase control and discrete (relay) control. We develop multipurpose ice melting plants (MIMPs) with discrete control for alternate and simultaneous glaze ice melting on a three-phase OHL and insulated earth wire, as well as on multiple grounded wires induced by the overfrequency current. Calculation formulas of the admissible current were proposed. Coordination procedure of the permissible load for all elements of the glaze ice melting pattern (GIMP) is given: OHL wires, the IMP, and a power transformer. The GIMP development procedure suitable for two types of controllable IMPs and for two transformers of different powers–an already present one and recommended new one–is considered in a specific context. Conclusions about the advantages of MIMP are drawn made on the basis of comparative analysis of four GIMP variants, and recommendations on the mode of application are given.



Modern methods and means for nondestructive testing of the quality of power semiconductor devices
Аннотация
Modern methods and means for designing devices for nondestructive testing of parameters of power semiconductor devices are described. A new method for determining the junction–case thermal resistance from the transition function of a thermosensitive parameter is presented. The operating principle of a specialized digital system for controlling and displaying the vibration frequency and linear accelerations during testing of the absence of freely moving particles, short circuits, and breaks in the circuits of electrodes is presented. The function of digital filtering of a signal that is formed by the sensor–accelerometer board is considered. A new method for the formation of a single shock-current pulse is described that is based on the use of the principle of a discrete superposition of charges in the electric circuit of the secondary winding of a power pulse transformer. The principle of the formation of a test voltage pulse in a test-pulse generator of the software–hardware complex for the automatic assignment of grades, which is based on the implementation of the pulse-amplitude modulation of pulse parameters in a galvanically isolated power control loop, is presented.



Analysis of power and energy loss based on long line equations
Аннотация
Expressions for power loss in a transmission power line are obtained based on the classical equations of a long line. It is shown that the loss and their components (in resistance and conductivity) consist of four terms depending on the square of current, the square of voltage, and the values of active and reactive power. The use of probability theory made it possible to obtain an expression to calculate the energy loss in the line characterized by a small methodological error. In addition, an approach was shown to reducing the energy loss in extrahigh voltage lines by control via reactive power flow using flexible alternative current transmission systems (FACTS).



Design and testing of heavy pulse current switches based on photothyristors
Аннотация
This article presents the results of testing heavy pulse current switches based on photothyristors. Transient processes are considered that are observed in the semiconductor switch when the capacitor is discharged upon inductance and with a signal-shaping network with an inductor and crowbar diodes. The limit currents are found for the semiconductor structure, at which thermal generation peaks are observed in oscillograph records of direct voltage drop. The energizing of the photothyristor is analyzed. The need for forcing RC circuits to ensure fast and steady transition of the semiconductor structure to the conductive state is shown. The transient process observed at reverse recovery of photothyristors in the discharge circuit with inductance is considered. The need for snubber circuits to suppress pulse overvoltage is established. The particulars of the transient switching of current to the crowbar diodes and the generation of pulse overvoltages at reverse recovery of photothyristors are considered for a discharge circuit with crowbar diodes. The parameters of snubber circuits to suppress these overvoltages are determined. The validity of the accepted engineering solutions is confirmed by the results of tests at switching of a pulse current of up to 100 kA.



Electromechanical energy conversion in a system with a bulk high-temperature superconductor. Part 2. Device operation analysis
Аннотация
The operation of a linear electromechanical vibration device with a part made of a high-temperature superconducting (HTS) material is analyzed. Converter models considered in the first part of this paper [1] are used in the calculations. The parameters of the model of HTS material properties are determined by comparison of the data obtained by calculations and by experimental investigations of force interactions in the laboratory device model. Functions of flux linkage and current force in the coil and permanent magnet movements are calculated for a macroscopic model based on analysis of the electromagnetic field. The calculation results of the operation parameters of the electromechanical converter are shown in the form of amplitude-frequency characteristics of the current in the coil, the permanent magnet movement amplitude, and electrical and mechanical power. Dependences of powers, efficiency, and current phase on the active mechanical load on the resonant frequency are determined. The obtained characteristics are compared with simulation data of a similar converter without the HTS element. It is concluded that the HTS elements significantly change the parameters of the conversion of electrical energy into mechanical energy. It is shown that the electromechanical converters with bulk HTS elements can be more efficient than converters of traditional design.



Marine electrical power industry with renewable energy carriers. Part 1. Wind and wave turbines of offshore power plants
Аннотация
The paper is devoted to offshore wind and wave power plants as an alternative to fossil hydrocarbon power engineering. It reports classifications and an analytical survey of the state-of-the-art of main types of offshore wind and wave turbines. The features of horizontal and vertical axes turbines constructions are described. Comparison of these two types of turbines has revealed the vertical axes design advantage since their height is two to three times less and its stability, accordingly, is higher. This allows expensive concrete tower constructions to be avoided and floating pontoons to be used, which is especially important for deep-water areas. The advantages of a two-contour wind turbine consisting of a fixed stator and a rotor directly connected with an electrical generator are highlighted. Due to the special “soaring in air” block construction of the turbine, the pressure on the seabed foundation is considerably reduced, allowing all the supporting structure for a floating pontoon to be replaced. The designs of wave turbines with direct and indirect operation are considered as well, the principles of harnessing marine wave energy are discussed and industrial prototypes of power plants of foreign firms are presented. With the help of analytical expressions, the evaluation of power performances is executed and a comparison of the power density criterion of wave energy with other kinds of renewable energy is indicated. It appears that the energy density of sea waves is an order greater of similar magnitude of wind and solar energy. On the basis of the idea of floating structures, the principles of designing hybrid and cluster offshore wind and wave power stations are suggested, where, with the help of power electronics and information technology, the electric energy of separate turbogenerators is integrated into a marine power pool system with HVDC underwater cable transmission to the consumers of a continental zone.



A technique for determining the parameters of a test loop for automated tests of electric apparatuses
Аннотация
According to the standards of the International Electrotechnical Commission (IEC) and Russian national standards, test loop parameters (time constant or power factor) for testing electrical apparatuses in the three-phase short-circuit (SC) mode are determined by the graphic-analytical technique. This technique is not suitable for automated tests. In addition, the precision of measuring the loop parameters is largely determined by the instant of SC occurrence. The procedures proposed in this article to determine the test loop parameters do not possess the flaws typical of the graphic-analytical technique. These drawbacks restrict one to the algorithm of SC current analysis in the initial period, or the so-called “S function” (the curve of the sum of the squared instant values of three-phase system currents), or the curve of the total instant power in the test circuit. A common feature of the indicated functions is autonomous behavior in the transient mode, as well as the instant of SC occurrence and informativity for determining the loop parameters. The proposed procedures make it possible to find, by mathematical processing of discrete current values, the power factor and the current value of the symmetrical test current component only 16 ms after the beginning of the transient process. The new procedures can be easily used in automated tests and will make possible more precise calculations of the test loop parameters.



An algorithm for determining the optimal moment to start recharging the accumulator battery in a diesel-photovoltaic power supply autonomous system
Аннотация
Currently, a problem related to the lack of centralized power supply in some regions of the Russian Federation is quite urgent. Existing technologies entail the use of diesel power plants, which are very expensive to maintain. In order to improve efficiency of such autonomous plants, this article suggests modernizing them by introducing photovoltaic systems and lead-acid batteries. For optimal functioning of these accumulator batteries, their specific features must be taken into account, along with possibilities of other power sources that make up parts of the power generating system. Thus, the automated system of control for such plants should have information obtained from various meteorological observations (data on insolation) and related to specific features of accumulator battery charges and discharges. This article offers a unique algorithm of determining an optimal moment to start charging an accumulator battery, which enables more efficient use of the generated energy to recover the state-of-charge of the electricity accumulator. According to the results of an efficiency assessment completed in Matlab regarding the use of this algorithm, fuel savings for an additional source (if it takes the form of a diesel power plant) reach 68.9% in the period of active insolation.


