Zlatko Maljković

The impact of the induction motor on short-circuit current

Simplified analytical models for calculation of the induction motors short-circuit current are presented. Laboratory tests have been performed on two induction motors with low power rating, 26 kW and 122 kW, respectively, in order to measure their short-circuit current. Results calculated according to the available literature have been compared to those acquired by testing. Calculations have also been made for a high-voltage induction motor rated 1250 kW, whose parameters have been known.

Detection of inter-coil short circuits in synchronous machine armature winding on the basis of analysis of machine magnetic field

This paper deals with detection of inter-coil short circuits in the synchronous machine armature winding, for the machines having the armature winding with coils, based on the analysis of the magnetic field present in the machine. Applying FEM (finite element method) [4] to the generator model, magnetic field wave forms in the machine have been calculated for every point of interest, under correct and faulty conditions. Selection of the stated points has been planned with the intention to reach a correspondence of the points of interest for flux density among the calculated points and points accessible for measuring with Hall sensors in the actual machine. Comparison of results shows changes in magnetic fields in the machine caused by analyzed faults. The results of calculations are confirmed by measurements on a real machine that is altered in a way that it is possible to simulate inter-coil short circuits of one or more coil turns of the armature winding. The aim of this study is creation of a contribution to the knowledge portfolio pertaining to detection of rotation machines failures and faults, or, in other words development and improvement of monitoring systems in charge of surveillance of rotation machine condition.

THE APPLICATION OF FINITE ELEMENT METHOD FOR MORE ACCURATE CALCULATION AND ANALYSIS OF TURBOGENERATOR PARAMETERS

The paper describes a computation of basic electromagnetic parameters of a turbogenerator using 2D finite element method with completely automated preprocessing. The results obtained by 2D method are compared to the ones obtained by classical (analytical) method and to the measured values from tests carried out on a 194 MVA turbogenerator manufactured by KONCAR-Generatori, Zagreb, Croatia. It appears that finite element method combined with analytical method gives more accurate results than analytical method and that the computation time can be quite acceptable.

Asynchronous starting process of hydro-generator

Paper gives simulation analysis of starting process for two synchronous machines. Reasons for motor and compensator modes of work and for asynchronous starting are presented. Matlab Simulink model including synchronous machine, excitation, transformer, electrical grid, measuring units and circuit breaker is built. This paper also gives discussion about results of simulation, influence of parameters and compare to measured values.

Diesel-generator-units dynamic analysis during the start-up of induction motors drives

The paper analyses the dynamics of generator-units during start-up of the induction motor drives. A unique mathematical model of integral motor drives has been developed, consisting of: a diesel engine, a synchronous generator and two non-regulated motor drives fed directly from generator-unit terminals. The aim of this paper is to compare dynamics behaviours of the generator-units during starting the second induction motor at the moment when the instantaneous electromagnetic torque of the synchronous generator reached various values

Torsional oscillations of the turbine-generator due to network faults

A model of the electromechanical system, suitable for the analysis of torsional oscillations due to the power systems faults, is established. Results of an example of computer simulation of transient torsional torques in the shaft-line due to a three-phase fault and the subsequent fault clearing, as obtained by the model, are presented. Effect of chosen fault clearing time is discussed.

Measurement of hydro-generator's end region temperature

Paper presents results of measurements of hydrogenerators end region steady state temperatures. Measurements were carried out in case of two hydro-generators, 65 MVA and 40 MVA respectively, installed in the same power plant. Four thermal probes were placed in each of the generators. Some of the tests, carried out for under-excited load conditions, had to be interrupted because the temperature of the end region exceeded 130degC. Results indicate that end region temperature should be monitored.

Induction motor's contribution to short circuit current

Simplified analytical models for calculation of the induction motors momentary short circuit current are presented. Laboratory tests have been performed on two induction motors, in order to measure their contribution to short-circuit current. Results calculated according to the available literature have been compared to those acquired by testing.

Large turbogenerator's synchronous reactance's load dependence determined by measurements

The paper presents research on underexcited turbogenerator operation capability. Measurements of basic electrical values for various loads have been carried out in case of 247 MVA turbogenerator. Synchronous reactance for various loads has been determined from measurements. Its influence on underexcited operation limits has been evaluated.

Analysis of synchronous generator stability in case of separate and self-excitation system

The paper presents the mathematical model of the electric power system with several synchronous generators. It enables the analysis of stability in the circumstances of large disturbance in a power system. The analysis has been performed for the generator with separate excitation and the generator with self-excitation.