Vol 89, No 2 (2018)

The main tendency in transport development is a move toward electric or hybrid propulsion, which is due to the increased requirements relating to the ecological effects and efficiency of transport systems. A key parameter that determines the prospects of electric transport is the specific power of electric machines (generators and motors). Thus, e.g., electric machines with a specific power higher than 20 kW/kg are necessary to produce electrical aircraft. Studies have shown that, during long operation, such magnitudes of specific power can be achieved with the use of cryogenic cooling and modern high-temperature superconductors (HTSCs) in electric motors and generators. In addition, the critical properties of superconductors should be taken into account, which leads to scientific and engineering problems. In particular, the HTSC stator winding should be made of coils in the form of racetracks. This can be done in a machine with a number of grooves per pole and a phase less than unity. In this work, the circuit of such completely superconducting electric machine with high specific power has been considered. The analytical technique of calculations of the main parameters has been suggested. The obtained expressions allow one to analyze the influence of number of pole pairs, superconductor properties, and main dimensions of a machine on the specific power. The results of the finite-element modeling of a completely superconducting electric machine have been considered.

This article considers the characteristic features of the electric-energy systems of the dynamicpositioning drilling vessels Stena Drillmax of Samsung Heavy Industry dockyard, Discoverer Clear Leader of DSME-DAEWOO shipbuilding and Marine Engineering dockyard, and Pacific Scirocco of Maersk Viking dockyard. The electric-energy systems of the drilling vessels include four to eight generator sets connected to the main electric switchboards located in isolated machine compartments separated from each other by watertight and fire-resistant bulkheads to increase the survivability. The propulsion system includes, as a rule, six azimuth thrusters with semiconductor frequency converters. The main ways in which modernization is carried out of drilling-vessel electric-energy systems are to ensure the operation of the vessel power plants on a common bus without reducing the reliability of the power supply of the positioning system and realizing the idea of the split power islands in the electric-energy system using a modernized monitoring and protection system for diesel generators (AGS, AGP blocks), a system of electrical distribution, and a more efficient algorithm of functioning of the PMS automation system, which in the case of the accident allows localizing the emergency area within one main switchboard without deenergization.

The properties of ac voltage stabilizers based on an inverting pulsed converter in the presence of input voltage waveform distortions and sharp dips of voltage are estimated. The stabilizer performance was determined on the basis of the limiting continuous model thereof considered in Part I of this paper. For correction of the voltage waveform and elimination of sharp short-term surges and dips of the stabilizer output voltage, control of the instant output voltage is introduced to regulate the relative times that the key stays in extreme positions depending on the relation between the instant input voltage value and the selected output voltage. It is established that the stabilizer properties are influenced mainly by variable coefficients of the differential equations describing the limiting continuous model of the stabilizer. It is shown that, if the input voltage waveform is distorted because of periodic variations of the coefficients of differential equations, the output voltage will also contain high-order harmonics. Their intensity decreases with decreasing electrical impedance of the choke. It is also shown that surges of the stabilizer voltage are almost instantly compensated because of the change of relative times the key stays in extreme positions. However, this does not eliminate transition processes occurring as a result of drastic changes of the coefficients of differential equations of the limiting continuous model of the system. Comparison of the processes in the real discrete stabilizer model and in the stabilizer limiting continuous model for a quite realistic switching frequency showed their practical identity.

The results of a theoretical and experimental investigation of the influence of damping and pitch plays on the dynamics of electromechanical systems in the zones of main, harmonic, and subharmonic resonances under parametrical disturbances are presented. Design models of electromechanical systems taking into account spring linkages, pitch plays, mechanical damping, and inconstancy of a gear ratio and reduction radius are proposed. The equations and structural schematics describing the movement of electromechanical systems under consideration in the initial values and adopted system of generalized parameters and relative units are presented. The electric drive is described by a linear mechanical characteristic taking into account the electromagnetic inertia of power circuits. The problems of linearization of electromechanical systems under parametric disturbances are considered, and the zone parameters are revealed under which it is possible. The analytical relationships for determining the optimum parameters of electric drive and the estimation of resonant amplitudes of oscillations of the elastic torque are obtained. Results of analysis of the influence of pitch-play formation on the oscillations in the zones of main and subharmonic resonances are presented. Features of these oscillations related to the magnitude of average load of transmissions and the direction of change in the frequency of parametric disturbances are considered. The reliability of theoretical regulations and conclusions of the article are confirmed by the results of industrial experience in the use of various circuits of a reduction-gear electric drive of rotation of an excavator under parametric disturbances caused by a gear wheel meshing with the gear ring.

A simple means of protection of a powerful single-phase transformer with integral magnetic transformers has been suggested. The protection has a high sensitivity to the interwinding failure and is based on the measurements of unsymmetry of the leakage magnetic fluxes of transformer windings. This magnetic unsymmetry is determined by the difference of electromotive forces of windings of two magnetic transformers placed symmetrically with respect to the symmetry plane of the protected transformer. It has been suggested to produce the magnetic transformers in the form of a single-layer winding with an alternating pitch, which is wound around a textolite round or rectangular body. The length of a magnetic transformer is taken to be equal to the length of a magnetic core, which allows one to provide independence of protection sensitivity on the location of closed turns on the transformer rod. To measure the difference of the emf of magnetic transformers, the circuit of comparison with a responsive element in the form of a TT-40/0.2 or RT1-P/0.15 current relay has been used. Methods to determine a trigger threshold and sensitivity of the protection to interwinding failure as well as to ironwork failure have been suggested.

Aspects of improving the accuracy of modeling extra-high-voltage (EHV) transmission-line (TLN) modes are considered using data from modern intelligent measurement systems. The methodological errors in modeling the parameters of EHV TLN modes are studied by line equations with distributed parameters. The proposed technique and algorithm of calculating EHV TLN modes rely on an equation of a line with distributed parameters, take account the actual characteristics of corona losses on voltage and the reactive corona effect, and make possible a higher accuracy of modeling. The accuracy of modeling EHV TLN modes is improved using a ladder equivalent circuit. A form of bicomponent equations for modeling overhead line (OHL) corona losses is proposed and justified. The first component is recorded in line equations with distributed parameters as conductivity, whereas the second component is presented as extra load. A program for computer-aided modeling of EHV TLN modes is developed. Results of calculations for 750-kV lines are presented.