Vol 87, No 8 (2016)

Development of the technical requirements for arc suppression reactors (ASRs) used for the capacitive current compensation of the single-phase earth fault is a critical task. The corresponding GOST (State Standard) 19470–74 “Oil-Filled Arc Suppression Reactors. Technical Requirements” is no more valid; automatically controlled reactors (with adjustable spacing controlled by magnetic biasing) are the mainstream; and completely new reactor designs, with the capacitor adjustment in particular, have become available. The standard guide for the earth-fault current compensation [1], not taking into account new technologies, has become obsolete. This paper considers the current criteria for the ASR application in the 6- to 35-kV networks and proposes new ones. It is proposed to use the residual earth-fault current, but not the ASR detuning coefficient, as the major criterion for capacitive current compensation of the single-phase earth fault; in this case, new requirements for the ASR and the network conditions characterized by active phase-to-ground and harmonics content currents are specified taking into account the electrical safety regulations. The problem of capacitance asymmetry is considered absolutely and relatively, and it is shown that the use of ASRs controlled by magnetic biasing allows omitting the network balancing and limitation of the asymmetry voltage at the level of 0.75% of the phase voltage. It is proposed to take into account these recommendations during development of an earth-fault current compensation guide and general technical requirements for ASRs and automatic tuning systems.

Compensation of single-phase earth fault currents in 6- to 35-kV networks is one of the purposes of using arc suppressing reactors (ASRs). Nonlinear distortion current of the reactor contributes to the residual fault current, for which reason its minimization is a critical task during ASR design. Operation under the technical saturation mode of electrotechnical steel is a characteristic feature of biasing controlled ASRs. Moreover, the biasing current of the device contains the high harmonics components; the share of these components depends on the structure of the magnetic system and on the properties of the electrotechnical steel. This paper proposes an approach to optimization of the magnetic system of a biasing controlled ASR based on adjustment of the biasing characteristics of the magnetic core according to the results of experimental measurements of the harmonic composition of reactor currents within a wide biasing range. Analysis of the influence of the parameters of the combined shell–core magnetic system on the reactor distortion current is carried out. Results of experiments for obtaining a biasing characteristic aiming at calculation of the harmonic composition of the reactor current with minimum 10% error are given. An optimization calculation of the parameters of the RUOM reactor magnetic system sections was carried out that allowed reducing the distortion current to 4% within the whole control range (10–120%) of the reactor nominal power and to 1% within the range of 60–100% of the reactor nominal power.

Monitoring systems of power quality and operation mode parameters are currently being developed and widely introduced. These systems make it possible to receive needed information in different nodes of a grid in real time, as well as build up data archives over a long period of time. The presence of such information makes it possible to change the approach to short- and long-term control by distribution grids. This paper describes the possibilities of application of information obtained from a monitoring system to control distribution power grids using the example of reliability evaluation of power equipment to schedule the repairs, and active–adaptive voltage control system. The dependences are shown of probability of failure of power equipment on operation time under different types of load curves and power quality. The conclusion is drawn that the wear of main equipment significantly increases when it is operated in conditions of low power quality. The dependence is shown of changing repair and inspection frequency of equipment on operation time and operating conditions. This paper describes the structure and principles of operation of an active–adaptive voltage control system. As a test example, the amount of violations upon steady-state voltage deviations of power consumers in a distributed grid using different methods of voltage control in a power supply center are compared. It is shown that, at nonuniform load in the grid, the required voltage level cannot be provided by the counterload regulation method. The ease of use of a monitoring system of the power quality of operation mode parameters of power consumers makes it possible to use the control system providing a required voltage level for the greatest number of power consumers.

The prospects for use of energy cables with cross-linked polyethylene insulation (CLPE) and switching gears with solid insulation under direct and alternating current are considered. The main developments in the work of enterprises manufacturing cable products are listed, and their main characteristics are given. The advantages of cables lines with cross-linked polyethylene insulation over cable lines with paper–oil insulation are described: increased capacity, high permissible insulation temperature, smaller cable bend radius, smaller weight–size parameters, increased service life, the possibility of being laid at low temperatures, and high environmental characteristics. The global experience and main problems of application of cross-linked polyethylene insulation cables under direct high-voltage current are analyzed. The variants of performance of the insulation and structure of 6–35 kV switching gears of different producers are studied. Some functions of switching gear, typical structures, and equipment structure are listed, and the main test modes for insulation of separated section and units of the switching gears are described. Different types of solid insulation of complete switching gears (CSGs) of medium voltage are compared: with and without a grounded shield on the surface. Reduced weight–size parameters and increased electrical safety are identified as advantages of the structure with a shield. Data on perspective Russian development in the area of complete switching gears and solid insulation are presented, and the conclusions regarding their main advantages are drawn. The basic functional of the system of control and monitoring by new-generation switching gear of the is offered.

A cathode-directed streamer in air is modeled using the hypothesis that branching is initiated by large electron avalanches that develop in a strong electric field in the front of streamer head. A series of streamer discharge simulations are carried out using a three-dimensional numerical model. The possibility of streamer branching is shown as a result of the interaction with two electron avalanches that arise in front of its head. They are directed to the sides from streamer propagation direction. Such a mechanism of branching is brought about by the fact, that at the moment of contact with the streamer, the avalanches have already undergone an avalanche–streamer transition or are close to it. The equality of the number of electrons in these avalanches at the moment of contact is not important. If this equality is violated, branching is asymmetric. If one of the avalanches interacting with the streamer is far from the avalanche–streamer transition, it does not trigger perfect branching, but it may produce an underdeveloped branch that does not evolve further. The streamer trajectory then deviates toward a larger avalanche, interacting with it.

An express method of direct measurements of the current density distribution of axially symmetric electron beams is proposed. It is shown that use of the technique is urgently needed to improve the reproducibility of the results of electron-beam processing. Comparative analysis of existing methods to measure the parameters of electron beams used for technological purposes is carried out. A technique to restore a radial distribution of electron beam current density as well as a device to implement the technique is developed. The results of radial distribution recovery are analyzed in the case in which the initial distribution is given in the form of a model function of normal distribution. An algorithm to determine estimated sizes of the area within which spatial distribution discretization is carried out is developed. Based on analysis of the experimental dependences, it is shown that the suggested numerical method can be applied to all types of axial-symmetric distributions. The nature of errors occurring after distribution function recovery is analyzed. A technological projection of express diagnostic systems for the processing electron beams is made taking into account parameters of the existing element base.