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TECHNICAL PAPERS

Rotor Dynamic Analysis of an Eccentric Hydropower Generator With Damper Winding for Reactive Load

[+] Author and Article Information
Martin Karlsson

Division of Computer Aided Design, Polhem Laboratory, Luleaa University of Technology, Luleaa, Norrbotten 97187, Swedenkarmar@ltu.se

Jan-Olov Aidanpää

Division of Computer Aided Design, Polhem Laboratory, Luleaa University of Technology, Luleaa, Norrbotten 97187, Sweden

Richard Perers, Mats Leijon

Department of Electricity, Aangstroem Laboratory, Uppsala University, Uppsala 751 21, Sweden

J. Appl. Mech 74(6), 1178-1186 (Feb 08, 2007) (9 pages) doi:10.1115/1.2723822 History: Received February 19, 2006; Revised February 08, 2007

Asymmetry in the magnetic circuit, around the air gap circumference, in a hydroelectric generator will give rise to a unbalanced magnetic pull. In this paper, a hydropower rotor system is modeled and the influence of electro-mechanical forces due to overexcitation is analyzed. The active power has been kept constant and the rotor excitation has been changed in order to vary the output of reactive power. The electromagnetic field is solved with the finite element method. Two electromagnetic models are compared: one with and one without damper winding. The mechanical model of the generator consists of a four degrees of freedom rigid disk connected to an elastic shaft supported by two bearings with linear properties. It has been found that the unbalanced magnetic pull slightly increases for reactive loads resulting in a decrease of natural frequencies and an increase of unbalance response. When the damper winding is included, the magnetic pull will decrease compared to the model without damper winding, and the pull force has two components: one radial and one tangential. The tangential component can influence the stability of the mechanical system for a range of design parameters.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Static rotor eccentricity

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Figure 13

Stability region of the rotor when Q=8MVAr, γ=0.08, variation of α and l∕h for simulation with (a) and without (b) damper windings. The stable region is white and the unstable is black.

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Figure 12

Stability region of the rotor when Q=0MVAr, γ=0.08, variation of α and l∕h. For simulation with (a) and without (b) damper windings. The stable region is white and the unstable is black.

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Figure 11

Stability region of the rotor when α=0.3, l∕h=0, and variation of γ, for simulations with (a) and without (b) damper windings

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Figure 10

Stability region of the rotor when α=0.1, l∕h=0, and variation of γ, for simulations with (a) and without (b) damper windings

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Figure 9

Unbalance response when α=0.3 and l∕h=−0.50, −0.25, 0.00, 0.25, 0.50, for the rotor system for 9MW active power, varying reactive power and electrical model with (a) and without (b) damper winding

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Figure 8

Unbalance response when α=0.1 and l∕h=−0.50, −0.25, 0.00, 0.25, 0.50, for the rotor system for 9MW active power, varying reactive power and electrical model with (a) and without (b) damper winding

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Figure 7

First forward natural frequency when α=0.3 and l∕h=−0.50, −0.25, 0.00, 0.25, 0.50, for the rotor system for 9MW active power, varying reactive power and electrical model with (a) and without (b) damper winding

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Figure 6

First forward natural frequency when α=0.1 and l∕h=−0.50, −0.25, 0.00, 0.25, 0.50, for the rotor system for 9MW active power, varying reactive power and electrical model with (a) and without (b) damper winding

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Figure 5

The radial Fy, tangential Fx, and resulting F force on the rotor for 9MW active power and varying reactive power, solved with (a) and without (b) damper winding. (Note that there will not be a tangential contribution to the total unbalance magnetic pull for the calculation without damper.)

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Figure 4

Magnetic field around one pole obtained from calculations

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Figure 3

Part of the computational mesh for the electric field

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