Abstract
This paper compares the short-circuit performance of superconducting (SC) generators with three different topologies, i.e. iron-cored stator and rotor, iron-cored stator and air-cored rotor, and air-cored stator and rotor. The analysis is based on three-phase short-circuit fault, and finite element analysis is used for simulation. Following the introduction of specifications of generators, the short-circuit performances of different topologies are analysed and compared, with the field winding excited by voltage and current excitation sources, respectively. It shows that the short-circuit performance can be improved by limiting the field current.
Highlights
Due to high power density of superconducting (SC) synchronous generators, they are being considered for marine applications and wind turbines, which have tough requirements for the size and weight of the machine.For the design of SC generators, much attention has to be paid to the performances under different types of fault conditions, they are rare and short-lasting
Where ia is the amplitude of phase steady current, E0 is the phase electromotive force (EMF), xd is the d-axis impedance
For aircored stator and rotor topology, the stator teeth and rotor poles are made of some kind of material with permeability the same as vacuum
Summary
Due to high power density of superconducting (SC) synchronous generators, they are being considered for marine applications and wind turbines, which have tough requirements for the size and weight of the machine. The analysis of short-circuit performance is usually based on some kind of topology, and the field winding is excited by a voltage excitation source. Their short-circuit performances are compared in Sections 3 and 4, with the field winding excited by voltage and current sources, respectively. The investigated topologies include iron-cored stator and rotor, iron-cored stator and air-cored rotor, and air-cored stator and rotor They are optimised, respectively, according to the specification of 10 MW offshore direct-drive wind turbine. Before the short-circuit fault arises, the generator operates at rated condition, with rated three-phase currents imposed on the armature winding and the switches are off. It can be seen that the stator current is mainly for demagnetisation of field winding, since d-axis current is much larger than q-axis current, and the direction is opposite to that of excitation field
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