Stanislav Kocman

Interference between electric traction supply network and distribution power network - resonance phenomenon

Electric traction is one of the biggest appliances in power network and can have a significant influences on supply network. These influences include non-harmonic currents and voltages, unsymmetric loading of the three phase system or rapid fluctuation in power consumption. Traction network, feeding network, traction transformer and, in some cases, filtration-compensation unit, altogether form a system of inductivities, capacities and resistances. That is why resonances can occur in this system. This paper investigates these resonance phenomena in a traction transformer substation that feeds alternate electric traction. The paper includes a theoretical analysis of the problem, computer simulation, and results of measurements in the transformer substation where resonances were recorded.

Elimination of harmonics using multi-pulse rectifiers

Multi-pulse rectifiers are used in various technical applications for the harmonics reduction of the input current drawn from the network. The paper presents elimination principles of dominant harmonics for a twelve-pulse rectifier with Dd0y1 transformer and for an eighteen-pulse rectifier with Dy1z1+200z1−200 transformer. This paper also provides a comparison of the theoretical assumption of the harmonic eliminations to experimental results obtained using a three-phase source enabling to supply the tested circuits with almost purely sinusoidal voltage, to results obtained supplying tested rectifiers directly from the network and to the results from a simulation model using EMTP-ATP program.

Eighteen-pulse rectifiers for harmonic mitigation

Multi-pulses rectifiers are one of the technical solutions for harmonic mitigation in AC adjustable speed drives. 12-pulse, 18-pulse and 24-pulse rectifier topologies are used in various technical applications. The paper presents results from experimental measurements and results from simulations for two topologies of the eighteen-pulse rectifiers: with Dy1z1+200z1−200 and with Dd0diii0+200diii0−200 transformers. To simulate the behavior of the both eighteen-pulse rectifiers under various levels of voltage distortion a program written in FORTRAN in EMTP-ATP simulation program has been developed. Both experimental measurements and simulations demonstrate their high harmonic mitigation effectiveness. A comparison of the eighteen-pulse rectifiers with some other techniques for harmonic mitigation is also shown in the paper.

Efficiency evaluation of various assemblies of variable speed drive

The paper presents results of experimental measurements of efficiency of variable speed drive assemblies and their analyses. These configurations of the drive have been tested: without any filtering devices, with an input AC reactor and broadband passive harmonic filters, and with output filtering, such as output reactor or sine-wave filter, respectively. These filtering devices are used to match the requirements of drive electromagnetic compatibility; nevertheless, they have an influence on drive efficiency. An assumption of drive efficiency decrease in the case these devices were used was confirmed and analyzed in this paper. Efficiency of individual units of the variable speed drive is also shown.

Using broadband passive harmonic filters for harmonic mitigation in AC drives

Various technical solutions are used to reduce harmonics generated by variable speed drives (VSD). AC VSD belong to their very significant sources with negative influences on the quality of electrical energy at the point of their connection to the network. The paper presents measured results of two types of broadband passive harmonic filters energized from a it programmable three-phase power source Pacific 3120ASX and provides their comparison to the results from a simulation model using EMTP-ATP program. A possibility of applying broadband passive harmonic filter into a structure of a drive of conveyor belt in the coal treatment plant is also shown and compared to the present condition. The results present that the effectiveness of the filters to eliminate harmonics is very good. Nevertheless, it is considerably affected by the quality of supply voltage at the point of filter coupling.

Solutions to increase the efficiency of induction motors

This paper presents possibilities to increase the efficiency of three-phase squirrel cage induction motors. The necessary legislative requirements are stated in the first part of the paper, which are basically the main reason for efficiency increasing. After that a theoretical basis and explanation of the design for efficiency increasing follow. The final part presents the results of measurements on the concrete samples of induction motors of different efficiency classes, their comparison, evaluation and comparison with the limits prescribed by the relevant standards.

Induction motor modeling using COMSOL multiphysics

This paper presents a time-dependent simulation of three-phase squirrel cage induction motor using COMSOL Multiphysics software. Simulation was made for constant rotational velocity adjusted to the nominal one of the tested motor. The course of stator currents, currents in rotor bars and in rotor ring and course of motor torque is shown. Finite element method model, external electrical circuits and meshing is also shown. The values of stator current and motor torque are compared to their values from motor catalogue. As will be seen, the simulation results from COMSOL match the catalogue values rather well.

Using active filter for harmonic mitigation in power grid of industry plant

This paper describes one way of technical solutions which are used to reduce harmonics generated by variable speed drives (VSD). AC VSD belongs to their very significant sources with negative influences on the quality of electrical energy at the point of their connection to the network. The paper presents the calculation and design of required filter performance and also the measured results of applied active filter connected to power grid of industry plant.

Analysis and simulation of disturbance of excavator in sintering ore-storage yard

One link of the production chain of ironworks is sintering. There is a preparation of the ore charge in it, which is transported to the next conveyor system by the bucket excavator. The paper presents results of experimental measurements performed on the bucket loader drive, an analysis of the drive disturbance and an assessment of electrical energy quality at the point of the drive connection. This paper also provides a comparison of levels of monitored voltage characteristics obtained by the measurements to simulated ones, and to their compatibility levels stated in the standard CSN EN 61000-2-4 ed. 2: Environment - Compatibility levels in industrial plants for low-frequency conducted disturbances. Both measurement and simulation confirmed that used input reactor for harmonic mitigation in the drive structure has only very low impact on the level of drawn current and supply voltage distortion. In this paper a simulation is also done for a possibility of using broadband passive harmonic filters to reduce current and voltage distortion. The results show their significant impact on improving quality of drawn current by the drive and supply voltage at the point of its connection.

Impact of mains power quality on operation characteristics of induction motor

The paper deals with the impact of chosen main power quality indices, such as the voltage distortion, the voltage unbalance and the voltage dip on operation characteristics of an induction motor rated at 4 kW fed from the frequency converter and AC source. In this paper the motor efficiency and motor power factor are analyzed in dependence on the motor load at rated motor frequency and the maximum permitted standard levels of power quality indices. In particular, it is shown that the greatest impact on motor operation characteristics has the voltage dip, and that the motor efficiency decreases approximately linearly with the level of the voltage distortion and the voltage unbalance in the specific range of motor load. To distinguish the energy characteristic differences, we used the standard deviation.