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In ThIs arTIcle, The sTaTe of The arT In the variable-speed operation of hydropower plants is reviewed, with a focus on pumped-storage hydropower. relevant literature is reviewed to address the benefits of variable-speed operation for both power systems and hydropower facilities. Two main configurations to enable variable-speed operation-the doubly fed induction machine (DfIM) and the converter-fed synchronous machine (cfsM)are discussed and compared. The article addresses the technology and energy policies of the past, present, and future and points out how the motivation, services, value, and technology of variable-speed hydropower plants have been subject to considerable change.

In ThIs arTIcle, The sTaTe of The arT In the variable-speed operation of hydropower plants is reviewed, with a focus on pumped-storage hydropower. relevant literature is reviewed to address the benefits of variable-speed operation for both power systems and hydropower facilities. Two main configurations to enable variable-speed operation-the doubly fed induction machine (DfIM) and the converter-fed synchronous machine (cfsM)are discussed and compared. The article addresses the technology and energy policies of the past, present, and future and points out how the motivation, services, value, and technology of variable-speed hydropower plants have been subject to considerable change.

In this paper, the influence of slot harmonics on magnetic forces and vibration is studied in a 120-slot/116-pole low-speed PM machine at no-load. It is shown how the lowest mode of vibration is produced at no-load due to slotting. Comparing the cases of open slots, semi-closed slots and magnetic wedges, the effect of slot closure on radial forces and torque production capability is discussed. Magnetic flux distribution in the airgap is computed using finite element analysis. Spatial harmonics due to slotting are investigated in different cases. Maxwell's stress tensor is employed to calculate radial and tangential components of the force density in the airgap. Spatial distribution of the total forces on the teeth and also time-dependent force waveform on one tooth are analyzed and discussed for different cases. It is shown how the magnitude of the lowest mode of vibration is reduced in the case of using semi-closed slots and magnetic wedges. Tangential force density distribution and torque production capability are also discussed. Structural analysis is presented to compute the maximum amplitude of the stator deformations due to the radial forces. Experimental results of the prototype generator are presented verifying the existence of the lowest mode of vibration at no-load because of the slot harmonics.

Abstract-In this paper, winding function method (WFM), applied to a faulted synchronous generator, is modified and is used for online diagnosis of mixed eccentricity fault. For the first time, the static and mixed eccentricities are modeled in synchronous generators. A modified winding function (MWF) method introduced here is more precise compared with previous methods. This MWF enables to compute the air gap magnetic permeance accurately. Here, two or three terms of the infinity permeance series have not been used, but a closed form equation is employed for permeance evaluation. This leads to a very precise computation of the inductances of the faulted machine. Self inductances of the stator and rotor, mutual inductance of two stator phases and the mutual inductance of rotor and stator are obtained. Meanwhile, it is shown that static, dynamic and mixed eccentricities lead to the increase of the amplitude and occurrence of the distortion in the aforementioned inductances. Since calculation of inductances is the most important step for fault diagnosis of the machine, the proposed method improves the on-line diagnosis of the fault. Meanwhile, the spectrum analysis of stator current, obtained from experimental results, is illustrated.