Consideration of design and operation on rotational flux density distributions in hydro generator stators

Core losses in an electrical machine vary depending on the type of material, frequency and flux density. Loss prediction using pulsating models is insufficient for estimating core losses in a machine since it does not take into account rotational core losses. Moreover the superposition of pulsating losses in the radial and tangential direction overestimates losses especially at higher flux densities. The objective of this paper is to study the rotational flux density distribution in the stator of a generator under different operating conditions. The distribution of rotational flux in a large hydro generator stator is studied by plotting the aspect ratio. It was found that increasing the yoke length increases the area experiencing rotational flux. Varying the air gap and output power showed slight changes in the rotational flux distribution. However they have an effect on the flux magnitude and harmonics which potentially increase the total losses. Dimensions and operating conditions of the machine therefore affect the total core losses.