Methods for calculating electric losses in asynchronous and synchronous electric drives are presented, as well as electric drive control algorithms based on synchronous reluctance machines with switching of magnetic flux and excitation winding on the stator and asynchronous motors by the criterion of minimum losses are proposed. It is shown that minimal losses are possible with control modes BLDC-mode with two-phase switching windings (BLDC 2) and power windings from a three-phase current source (BLAC mode) according to the following indicators: average torque, ripple torque, the number of keys of the power converter. It is shown that the BLAC-control mode turned out to be the best in the nominal operating mode. The average torque value turned out to be 7% higher than in BLDC 2 mode, the maximum voltage value of the converter was 2 times lower, which allows you to select keys for a lower voltage, the maximum voltage increment value of the converter was 6 times lower, which reduces the requirements for speed control loop current drive. It is shown that in the overload mode, a control algorithm with sequential excitation is preferable, when the current in the excitation winding increases in proportion to the current in the power windings, which has significantly reduced electrical losses. In this case, the torque of the electric drive increases almost linearly, without visible restrictions on the overload capacity and, at a five-fold current overload, amounts to 4.3 nominal values.

Features of Loss Calculation in Mechatronic Modules on the Basis of Synchronous Reluctance and Induction AC Electric Drives

An analysis of existing technologies in the production of medium-voltage power cables with crosslinked polyethylene insulation (XLPE insulated power cables) was carried out, which showed that the strength and heat-resistant characteristics of cable insulation systems with silane crosslinked polyethylene and peroxide insulation are almost the same. Therefore, the use of a cheaper, but not inferior in terms of basic parameters technology may become preferable in the production of XLPE insulated power cables for a voltage of 10 kV. The features of the XLPE insulated power cables functioning for various screens connection and grounding schemes are considered. It is proposed to introduce into the regulatory documents for single-core XLPE insulated power cables the order of cable lengths with one-sided grounding of the screen and with the partition of the cable screen into sections. Since the production of three-core XLPE insulated power cables with sector-shaped conductors and their common screen has been mastered at present, it is necessary to consider their use as an alternative to single-core cables.

Power Cables with Crosslinked Polyethylene Insulation and Their Screens Grounding Features

High-performance flux-switching DC motors for energy facilities

In this paper, we calculate a mathematical model of the transition process of forming the temperature field of a cable line with insulation from cross-linked polyethylene at various currents close to the maximum allowed. The model of underground cable laying with a triangle in standard climatic conditions is considered. When the current is applied, the temperature difference between the medium and the cable is a solution to the ordinary linear differential equation, which implies that the thermal balance of the system occurs 30 min after the start of operation. The model of formation of the thermal field of a cable using an equivalent screen shows proportionally close heating of the core and the screen. The temperature change of all cable elements describes a two-dimensional parabolic type equation with zero Neumann boundary conditions. The simulation is done in PDETool Matlab. Empirically, the heating time of the cable core to temperatures of 27, 40, 50° was determined. Numerical modeling takes into account the change in the thermophysical parameters of the cable with increasing temperature. For this, the simulation time is divided into three iterations with updating of the initial conditions and parameters of the equation. The proposed model makes it possible to evaluate the limiting currents of the cable load, possible changes in the materials used, laying methods, and determine the interdependence of the model parameters. Thermal analysis is used to solve operational problems, such as determining the values of the cross-sectional area of the cable and screen, methods of connecting and grounding the shielding shells.

Mathematical Modeling of Transient Heating Processes in the System of Three Single-Pole Cables

The choice of the ground circuit of a shield that gets rid of capacity losses is becoming especially urgent to increase the transmission capacity of lines with cross-linked polyethylene insulation. Ground systems of shields of the single-phase high-voltage power cables are studied. A mathematical model to select the section of the electric conductor for single-wire power cables for a voltage of 6–500 kV is suggested which takes into account the connection circuit of the shield permits allows one to determine the capacity losses and induced voltage on the shield. The method of selection of energy-efficient grounding systems of the shield of the three-phase group is found on the basis of the mathematical model. A selection criterion is suggested determining the relative rate of return of the “open” ground system with no currents in the shields over against the “closed” system in the shields of which parasitic currents flow.

I. M. Khevsuriani

Papers

Influence of the shield grounding system on choice of section