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Abstract-The maximum allowed per unit value of the synchronous reactance of a synchronous generator is normally decided by the grid codes in order to maintain the stability of the system. For the converter-fed synchronous hydrogenerator, the steady state stability can be maintained by the frequency converter. In this paper the constraint on the synchronous reactance is relaxed from 1.2 per unit to 2.0 per unit and then removed altogether. The cost of the active materials and the net present value of the cost of losses are calculated for each case and compared. Three different nominal frequencies are also used to find which one gives the lowest total cost. The total generator cost is reduced when the synchronous reactance is increased. The lowest cost of the 50 Hz designs are lower than the cost of the 25 and 75 Hz designs.

This paper investigates the effect of converter operation on AC copper losses in the stator and damper windings of a large hydrogenerator. Stator currents are computed using finite element simulations. The computed current waveforms are used as an input to estimate the AC copper losses in the stator due to converter operation using an analytical approach. Damperbar losses are calculated directly in the finite element analysis. The generator is simulated with a two-level voltage source converter and a three-level neutral-point-clamped converter topology. Different carrier frequencies are used to investigate their effect on the AC copper loss. Methods for handling these additional losses are discussed and analysed.

Abstract-This paper investigates the flux density and radial force spatial harmonics in large salient pole synchronous hydrogenerators. Vibration due to magnetic forces are mainly caused by low order harmonics in the airgap flux density distribution. The influence of winding layout and airgap length on the lowest order radial force component are analysed. Airgap flux density and radial force density distributions of three different generators are computed using finite element calculations. The flux density components that contributes to the lowest order force component, and the source for these harmonic components, are investigated. It is found that reducing the airgap length leads to a less than proportional increase in the lowest order radial force component. A rearrangement of the winding layout is found to be an effective method for reducing the lowest order radial force component.