A field method for determining parameters and characteristics of a synchronous machine

The paper presents field methods for determining electromagnetic parameters (inductances, resistances and time constants) of a synchronous generator mathematical model containing one equivalent damper circuit in each rotor axis. The magnetostatic and the electromagnetic harmonic field distributions calculated by the finite element method were used. Nonlinear characteristics of machine inductances were presented which illustrate the saturation effect. Particular attention were drawn to the problems of determining subtransient time constants of the generator

Calculation of axial magnetic flux in induction machine by finite element method

In the paper results of finite-element calculations of the electromagnetic field in a squirrel-cage induction motor with particular reference to the shaft flux were presented. A three-dimensional field-circuit model of the 300 kW induction motor was developed taking into account supplying the stator winding from the voltage source and the rotary motion of the rotor. Distribution of axial and radial components of the magnetic flux density in the end-winding region and the bearing region as well as transie nt waveforms of the shaft flux were computed at the initial period of the motor start-up

Estimation of Synchronous Generator Model Parameters Based on Analysis of Disturbance Waveforms Under Load Conditions With Use of the Finite Element Method

In the work there is presented a field-circuit model of a high power synchronous generator which enables determining the waveforms of electromagnetic quantities in steady and transient states. Verification of the field-circuit model was performed based on comparison of the measured and calculated with finite element method waveforms at a step change of the voltage regulator reference voltage of the generator operating under no load conditions in Połaniec Power Plant. The dynamic waveforms of the generator operating in a power system under load conditions, in which the transient state was caused by a step change of the field voltage, were the basis for estimation of the generator model electromagnetic parameters. Estimation of the generator model parameters was performed with use of the least square method

A methodology for determining electromagnetic parameters of a synchronous machine based on analysis of transient waveforms obtained by the finite element method under no-load conditions

The paper presents the method for determining electromagnetic parameters of a high power synchronous machine based on analysis of transient waveforms caused by small disturbances in the field winding under no-load condition. The waveforms were calculated by the time-stepping finite element method when using a two-dimensional field-circuit model of the machine worked out in the Maxwell program of Ansoft Corporation. The model takes into account non-linear B-H characteristics of magnetic cores, eddy current action in solid parts of the rotor, the rotor motion, as well as the power supply of machine windings from voltage sources. The transient state was initiated by a change in the field voltage of several percents in the form of a step or pseudorandom signal (PRBS) at no load and constant rotor speed. Basing on the determined transient waveforms in the field-circuit model, the parameter estimation of the selected mathematical circuit models of the machine was performed using the least square method. An optimisation algorithm from the Matlab/Simulink package was applied to minimise the mean square error

Influence of squirrel cage faults on shaft voltage values in induction motors

The paper presents initial results of laboratory investigations. These results emphasize the intensification of the phenomena connected with bearing currents flow at different rotor cage damages. In the section 2 is presented the influence of rotor cage damages on the shaft voltage value. The subject of these studies was a low power induction motor (fig. 2), taking into consideration easiness and low costs of necessary modernization of it. On the figure 3 is presented the diagram of the shaft voltage and current measurement system. The measurements results are presented on the figures 5, 6. Conclusions drawn from laboratory researches are presented in chapter 3

Determination of synchronous generator nonlinear model parameters based on power rejection tests using a gradient optimization algorithm

The paper presents a method for determining electromagnetic parameters of different synchronous generator models based on dynamic waveforms measured at power rejection. Such a test can be performed safely under normal operating conditions of a generator working in a power plant. A generator model was investigated, expressed by reactances and time constants of steady, transient, and subtransient state in the d and q axes, as well as the circuit models (type (3,3) and (2,2)) expressed by resistances and inductances of stator, excitation, and equivalent rotor damping circuits windings. All these models approximately take into account the influence of magnetic core saturation. The least squares method was used for parameter estimation. There was minimized the objective function defined as the mean square error between the measured waveforms and the waveforms calculated based on the mathematical models. A method of determining the initial values of those state variables which also depend on the searched parameters is presented. To minimize the objective function, a gradient optimization algorithm finding local minima for a selected starting point was used. To get closer to the global minimum, calculations were repeated many times, taking into account the inequality constraints for the searched parameters. The paper presents the parameter estimation results and a comparison of the waveforms measured and calculated based on the final parameters for 200 MW and 50 MW turbogenerators

Shaft voltage calculations in a cage induction motor by the finite element method

In the paper results of finite-element calculations of the shaft voltage in a squirrel-cage induction motor were presented. A two-dimensional field-circuit model of the 300 kW induction motor was developed taking into account supplying the stator winding from the voltage source and the rotary motion of the rotor. Calculations of transient waveforms of the shaft voltage and other electromagnetic and electromechanical quantities were performed during starting under no-load and rated load conditions. An influence of static and dynamic air-gap eccentricity was examined. Ways of the improvement in the accuracy of calculations were discussed

The analysis of bearing damage caused bearing currents

The negative influence of bearing currents on the durability of rolling bearings in the alternating current electric motors are shown. The reasons of bearing current formation in electric motors are given. Examples of bearing races damages of cooperating rolling bearing elements are presented. Analysis of dents distribution in the roller, roll-neck and ball bearing races are made. Conclusions drawn from laboratory researches are presented in chapter 6

Comparison of parameter estimation results of different synchronous generator models obtained from measurement tests

The paper presents comparison of estimation results of chosen parameters (in d axis) of the following synchronous generator models: GENROU (model of type XT) as well as (3.3) and (2.2) (models of type RL) using the disturbance waveforms obtained at a step change of the reference voltage of the synchronous generator voltage regulator working under no-load conditions in Power Plant Rybnik. The generator parameter estimation was performed in an iteration process in such a way that the dynamic waveforms calculated on a basis of those parameters approximated the measured waveforms with a given accuracy. The estimation process can be brought to minimisation of the objective function which is influenced by the differences between the measured and approximated waveforms at particular time instants

Influence of the air gap asymmetry on the values of shaft voltages and currents in high power induction motors

The paper presents the influence of the air gap asymmetry on the values of shaft voltages and currents. The investigations were performed with use of high power induction motor dSKgw 315 L-4 of 300 kW rated power and 1000 V rated voltage. In the section 1 are presented sorts of threats caused by bearing currents. Sorts of eccentricity of electrical machines are presented in section 2. In the section 3 the laboratory measurement system is described and applied measurement methods are presented as well. The results of laboratory investigations are presented in section 4. Conclusions drawn from investigations are placed in section 5