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

Abstract

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.

Study of generator modes effects on electric power quality and air gap

“…In addition to measurements in no-load mode and start-up load it is suggested to measure air-gap in SK mode with −20 MVAr or −30 MVAr reactive power and mode with 90 MW active power and −30MVAr reactive power. Martin Karlsson in his study showed that for reactive loads EMF should increase and as a result unbalance response will be also increasing [7]. Numerical values obtained from the experiment support that finding for the particular generation unit, since the greatest unbalance (Delta values in Table I) was still observed during modes with reactive power.…”

“…Kangro, T. Vaimann, A. Kallaste et al in their studies showed that air gap of generator determines the eccentricity of the generator and rotor form [8]. Based on eccentricity studies [5,7], from Figure 3 one could conclude that measured rotor has dynamic eccentricity and could be further analyzed as elliptical rotor displaced. Figure 1 and Figure 2 illustrate some discrepancy between upper and lower sensor measurements in synchronous compensator mode.…”

Vibration Characteristics of a Hydroelectric Generating System with Different Hydraulic-Mechanical-Electric Parameters in a Sudden Load Increasing Process

“…Considering the large area of the reservoir, it is assumed that the water levels of the upstream and downstream reservoirs are constant during the transient flow, and the pipe (1) Upstream and downstream reservoirs Considering the large area of the reservoir, it is assumed that the water levels of the upstream and downstream reservoirs are constant during the transient flow, and the pipe inlet head loss is ignored. The boundary conditions of the upstream and downstream reservoirs are [28]:…”

Overvoltages and power oscillations in hydro generators

“…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 [9]. 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.…”