Urban Lundin

Saturation Effects on Unbalanced Magnetic Pull in a Hydroelectric Generator With an Eccentric Rotor

We report an investigation of saturation effects on the unbalanced magnetic pull in a hydroelectric generator with 20% static eccentricity. We determine the magnetic pull force by the finite-element method in parallel with a simple analytical model for various no-load voltages and loads. Saturation significantly affects the magnitude of the unbalanced magnetic pull for high voltages and large loads.

Novel method of self‐interaction corrections in density functional calculations

It is demonstrated that the commonly applied self-interaction correction (SIC) used in density functional theory does not remove all self-interaction. We present as an alternative a novel method that, by construction, is totally free from self-interaction

Core Loss Prediction in Large Hydropower Generators: Influence of Rotational Fields

In this paper, we discuss the accuracy of several core loss models as compared to experimental data obtained from measurements on commercial hydropower generators. Our aim in this paper is twofold. First, we emphasize the problem of total core loss prediction by comparing the core loss figures obtained by different loss prediction schemes with measured no-load losses. Second, we examine the predicted net effect of bidirectional flux, i.e., the rotational loss. We show that the average degree of rotation in the stator core, and hence the rotational loss, is closely related to the stator slot geometry.

Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests

Four standard test procedures-the three phase short-circuit test , the field decrement test, the slip test, and the applied voltage test-for estimation of synchronous generator parameters have been implemented in a time-stepping finite-element software. In this paper, the main features of the implementation and the postprocessing of data are described. The validity of the application is demonstrated by comparison with test results from the commissioning of a large hydropower generator. The method is shown to be effective in estimating most parameters. Better representation of the exciter and the interpole connections of the damper circuit is believed to enhance the compliance even further.

Method for Modeling Time-Dependent Nonuniform Rotor/Stator Configurations in Electrical Machines

Nonuniform air gaps in electrical machines cause problems with forces and noise. There are a number of analytical and numerical methods to calculate the response due to nonuniform air gaps. In this paper, we present an efficient method based on an effective air gap permeability. Our unified method enables all nonuniform rotor-stator configurations to be simulated. We provide some results from simulations of static and dynamic eccentricity as well as irregularity.

Damper Winding Influence on Unbalanced Magnetic Pull in Salient Pole Generators With Rotor Eccentricity

The influence of three different damper winding configurations on unbalanced magnetic pull (UMP) in salient pole synchronous machines with rotor eccentricity has been investigated. Continuous and noncontinuous damper windings resulted in different damper winding currents, but their effect on the UMP was found to be very similar. Measurements of the UMP, damper bar currents, and air gap flux density were performed on a 12-pole generator with a static eccentricity under no-load conditions. Finite-element simulations of the different configurations detailing the damper winding induced flux changes are also presented.

Reduction of Unbalanced Magnetic Pull in Synchronous Machines due to Parallel Circuits

This paper describes an analysis of the damping of unbalanced magnetic pull (UMP) in salient pole synchronous machines due to parallel stator circuits. Measurements of the UMP and currents in the parallel circuits have been performed on a 12-pole generator with the stator displaced relative to the rotor, creating a static eccentricity, and the stator winding connected as one circuit or two parallel circuits. Experiments were done at no-load conditions. Two numerical studies of the force reduction are also presented, one using a finite-element code and one using a permeance model. A good correspondence between measured and simulated forces is obtained. Results indicate that the reduction of UMP is strongly dependent on the direction of unbalance relative to the line of separation of the stator circuits. Eddy currents induced in the rotor during operation were found to reduce the standstill UMP with more than 20%.

Design and construction of a synchronous generator test setup

This paper describes the design considerations underlying the construction of a flexible synchronous test generator setup to be used for electrical, magnetic and mechanical measurements. Practical solutions to enable such measurements are also provided. Damper bar currents, stator winding currents, air gap flux density and mechanical forces can be measured for different rotor eccentricities as well as for different damper bar and stator winding configurations. A simple comparative test of the effect of inter pole damper connections on the slot harmonics during no load has been performed.

On Permeance Modeling of Large Hydrogenerators With Application to Voltage Harmonics Prediction

In this paper, a permeance model that can be employed to estimate the no-load damper current loss and voltage waveform harmonics in large hydrogenerators is presented. The importance of modeling the damper magnetomotive force and inductances correctly is emphasized, and detailed descriptions are presented. The computed harmonics are compared with values obtained from time-stepped finite-element calculations and measured data. The results are in good agreement. The influence of pole-to-pole damper bar connections, and of the number of damper bars on the voltage waveform, is explained.

Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants

The dynamic behavior of hydropower plants participating in primary frequency control is investigated in this paper through frequency response, step response, and setpoint change tests on three Swedish hydropower plants. Gray-box system identification is used to estimate the parameters of simple linear models suitable for power system analysis and the major shortcomings of the linear models are discussed. It is found that frequency response tests with sinusoidal input signals give more reliable information about the dynamics of the plants than step response tests. It is also shown that backlash in the runner and guide vane regulating mechanisms are of great importance for the dynamic behavior of the plants, and that the incremental gain from guide vane opening to power varies considerably with the operation point.