Investigation of AC loss of superconducting field coils in a double-stator superconducting flux modulation generator by using T-A formulation based finite element method

Abstract

In order to reliably make use of superconductors in wind generators, a double-stator superconducting flux modulation generator is proposed here to avoid rotation of field coils and armature windings. The superconducting field coils are located in the inner stator while the armature windings are placed in the outer stator. In this way, the stationary-rotatory couplings of current and cryogenic coolants for superconducting field coils and/or armature windings are removed. Because of the modulation effect of the reluctance rotor between the two stators and the armature reaction field, moving AC magnetic fields are acted on superconducting coils in the inner stator. These moving AC magnetic fields are called magnetic field harmonics in the flux modulation generators. The frequencies of these harmonics are multiples of rotor mechanical frequency. Compared to synchronous superconducting generators, the amplitudes of the harmonics are higher. Even though methods to reduce the amplitudes of harmonics have been studied, the level of the AC loss in the superconducting field coils is still unknown. In this paper, numerical simulations based on the T–A formulation are used to estimate the AC loss of the superconducting field coils in a 10 MW double-stator superconducting flux modulation generator. It is found that by choosing a suitable working temperature, the AC loss of the superconducting field coils without any harmonic reduction methods is not very high, but eddy current loss of copper thermal shield inside the cryostat is significantly higher.

Preliminary design optimization of a fully superconducting motor based on disk-up-down-assembly magnets

“…In this section, the electromagnetic performances of the five motor designs were calculated through finite element software Maxwell with the magnetic vector potential as the dependent variable and the AC losses of the superconducting armature coils were evaluated through Comsol 5.6 based on T-A formulation [15].…”

“…They are generally located in the rotor as the magnetic poles. Up to now, the most widely used superconducting magnets in motors are wound coils [5,15]. The technology to manufacture the wound superconducting coils is quite advanced.…”

Critical current and loss character of quasi-isotropic strands with resistance

“…The MEMEP method can be used to calculate any material with a nonlinear E(J) relation, especially superconductors, as first reported in [24]. Compared with the H [25][26][27][28][29][30] and T-A formulation methods [31][32][33][34], the MEMEP method attempts to find the minimum value of the function for the change in current density between any two time steps rather than solving the PDEs directly. Hence, it can quickly adopt a much better mesh strategy to get higher-precision results [35][36][37][38][39].…”

An Electromagnetic Design of a Fully Superconducting Generator for Wind Application

“…As a result, there was no analytical formula for the superconducting coils in a generator. Hence, in order to evaluate the AC loss of the stator coils, the T-A formulation of Maxwell's equations implemented in COMSOL Multiphysics in 2D [14] was employed in the generator design obtained from the analytical model described above.…”

“…Hence, in this paper, an in-house code was developed to design superconducting wind generators, taking into account geometry, electromagnetics, superconducting properties, iron properties, and AC loss. The estimation of the AC loss is made through the T-A formulation of Maxwell's equations by employing finite elements within the whole generator domain [11][12][13][14]. This work addresses the design of a 10 MW fully superconducting direct-drive wind generator to present the model and is organized as follows.…”