Vol 87, No 6 (2016)

During research tests of vacuum interrupter chambers (vacuum interrupters, VIs), their breaking capacity is determined by bringing the chamber to a thermal failure, i.e., to a situation in which a VI is already unable to switch a current off and a safety switch of the test bench interrupts the current. Thus, the highest short-circuit current is defined, which can be interrupted by an opening switch with a VI under prescribed standard conditions. This current is characterized by the effective value of its periodic component and the fraction of the aperiodic component in the current curve. However, if in the case of a failure, some elements of the VI (or the chamber as a whole) are destroyed, this will impede analysis of the cause of this failure. This paper describes a test method in which the development of a failure is not allowed, and the risk of a failure is established on the basis of its primary features. It is shown that such features are a considerable burning-arc duration before the first arc-current zero and arc reignitions even at a low transient restoring voltage. It is also established that, for VI chambers with contacts that create an axial magnetic field, the rated breaking current can be determined using the failure criterion, for which the critical value of the electric charge, which is transferred through the vacuum arc before the first current zero, is adopted. This failure criterion makes it possible to reduce the number of tests that are needed for determining the rated breaking current. The calculated data for determining the values of the critical charge and the rated breaking current are presented.

To monitor the insulation of high-voltage equipment, different kinds of devices, including in situ ones, are used. This paper considers the possibility of using optical indicators—light emitters mounted on the insulation structure of high-voltage lines and substations—as such devices. The principle of operation of an optical indicator is as follows. The electric field distribution over an insulation structure changes with breakage of the integrity of its separate parts; when the potential difference at a damaged section decreases, the voltage at the undamaged part correspondingly increases. A faulty condition of the insulating structure can be determined using the light intensity of an indicator installed in the section of the insulating structure or pylon, since the luminance depends on the voltage drop across its terminals. Experiments showed that such insulation failure can visually be determined without using any additional devices, for example, during routine inspections. It is shown that it is possible to produce indicators that are easy to manufacture and do not require any additional maintenance.

The possibility of increasing overload capability and reducing power loss in a frequency-controlled synchronous electric drive operating in a continuous periodic mode is considered. A definition of a “continuous periodic mode” is given. A functional diagram of vector control system of synchronous electric drive is presented. The statement of a problem in the study of electric drives is formulated. A modeling method of a synchronous electric drive making it possible to recognize the maximum loads upon heating of a synchronous motor is described. Results of computer modeling of the continuous periodic operational mode of a salient pole motor with continuous and optimal regulation of armature magnetic flux are presented. The resource of synchronous motor is determined on the basis of the criterion of motor torque allowable upon heating. A comparative analysis of power loss of synchronous motor in the continuous periodic mode with continuous and optimal regulation of armature magnetic flux is carried out. The conclusion is drawn that the use of optimal regulation of armature magnetic flux in vector control systems of synchronous electric drives operating in continuous periodic mode is efficient.

The fundamentals of design procedure of performance data of controlled asynchronous motors (AMs) supplied with pulse voltage are stated in this article. The proposed model is based on a L-shaped equivalent circuit for each of harmonics, on which the curve of applied to a phase voltage is displayed. It is proposed to find the increase of magnetic iron loss caused by hysteresis in proportion to the peak value of the pulse voltage. The influence of PWM voltage on magnetic hysteresis loss is determined by using a coefficient depending on the effective values of fundamental and higher harmonics of the EMF and voltages, as well as the coefficient taking into account the increase of electrical resistance of iron due to the skin effect. In a similar way, it is proposed to take into account magnetic losses in the rotor that are occasioned only by the influence of higher harmonics. It is proposed to determine the increase of resistance and decrease of the inductance of short-circuited rotor of the influence of currents of higher harmonics by the well-known Interelectro methodology. The resulting values of consumption current, power factor, effective power, and consumption power of an asynchronous motor with pulse voltage are calculated taking into account the total effect of currents and voltages of fundamental and higher harmonics. Based on the methodology that we have laid out, a program was written and modeling was carried out of the operational characteristics of an asynchronous motor with a power of 180 W supplied by a PWM inverter with a fundamental frequency of 50 Hz. In addition, the harmonic composition of pulse voltage was obtained by processing the oscillograms taken from phase windings of the motor supplied by the frequency converter. To experimentally check of the proposed model, an experimental plant for loading the asynchronous motor was assembled and the operational characteristics of asynchronous motor with the fundamental harmonic of 50 Hz were determined. The experimental results showed satisfactory convergence with the calculated results that makes it possible to recommend the proposed methodology to evaluate the energy indices of frequencycontrolled asynchronous motors.

This article discusses the causes of cogging torque pulsations in a deenergized brushless dc motor (BLDC) with a tooth stator and magnetoelectricity stimulation. Based on the causes that we identify, we propose a method of reducing cogging torque pulsations in order to improve the rotation speed uniformity of a BLDC. The method is based on optimization of the number of stator slots, which determines the type of stator winding for a given number of poles in magneto-electric machines. For the maximum possible reduction of cogging torque pulsations, it is proposed to bevel the stator slots at an angle divisible by the main tooth harmonic period. All analytical calculations were performed with the use of numerical methods for mathematical modeling of the magnetic field in the magneto-electric machines with the use of Elcut specialized software. Based on the calculation results, recommendations for the design of a BLDC with a minimum level of cogging torque pulsations were elaborated. Our theoretical studies have been checked by experimental investigations of a DBM 142-18-3 motor and applied to the design of the BLDC (DBM series) manufactured by JSC Electroprivod, Kirov. Electric motors of DBM series are used as precision electric drives for metalworking equipment, where a high uniformity of rotation speed is a major requirement.

Features of energy conversion in the linear electromechanical vibration device with an element made of high-temperature superconducting (HTS) material are considered. A disk-shaped permanent magnet with axial magnetization moves inside a fixed circular coil, and a ceramic HTS element, also disk-shaped, is fixed at a distance from the permanent magnet. All converter elements are arranged coaxially. The HTS element transitions into a superconducting state in the magnetic field of the permanent magnet. The purpose of the investigation is to find the effect of the HTS element effect on the static and dynamic parameters of the converter by comparing the operation of the device with the HTS element and without it. Mathematical models are developed for the calculation of dynamic characteristics of the device in the Matlab/Simulink software environment for electrical and mechanical subsystems. The connection between the subsystems is defined by functions of flux linkage of the coil and the electromagnetic force, which are obtained by the analysis of the electromagnetic field by the method of spatial integral equations taking into account HTS material properties. A combined model of HTS material properties is proposed with two sources of magnetic fields (magnetization and current density), which is more universal than current only models.