US 12,332,314 B2
Generator fault detection method based on the characteristics of air gap magnetic flux density
Yuling He, Baoding (CN); Wen Zhang, Baoding (CN); Yong Li, Baoding (CN); Yifan Bai, Baoding (CN); Mingxing Xu, Baoding (CN); and Xiaolong Wang, Baoding (CN)
Assigned to North China Electric Power University (Baoding), Baoding (CN)
Filed by North China Electric Power University (Baoding), Baoding (CN)
Filed on Jun. 16, 2023, as Appl. No. 18/210,659.
Claims priority of application No. 202310425801.1 (CN), filed on Apr. 20, 2023.
Prior Publication US 2024/0369635 A1, Nov. 7, 2024
Int. Cl. G01R 31/34 (2020.01); H02K 11/215 (2016.01); H02K 29/08 (2006.01)
CPC G01R 31/343 (2013.01) [H02K 11/215 (2016.01); H02K 29/08 (2013.01); H02K 2201/03 (2013.01); H02K 2213/03 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A generator fault detection method based on characteristics of an air gap magnetic flux density, comprising the following steps:
S1: installing detection devices on a generator and building a test platform;
S2: obtaining an air gap magnetic flux density signal through the detection devices;
S3: transforming a time domain signal of the air gap magnetic flux density into a frequency domain signal by using a fast Fourier transform;
S4: confirming an operation condition of the generator through a comparison of time domain and frequency domain;
S5: obtaining a value of the air gap magnetic flux density by calculation, selecting, and then comparing a root mean square value of the air gap magnetic flux density under different working conditions with a root mean square value of the air gap magnetic flux density under normal condition to determine a degree of air gap eccentricity and a short circuit degree of a stator inter-turn short circuit fault; wherein in S5, the working conditions of the generator are divided into four types: normal condition, air gap radial eccentricity, air gap axial eccentricity, and stator inter-turn short circuit, wherein an expression of an air gap magnetomotive force of the generator in the above four conditions is calculated as follows:
ƒ(αm·t)
wherein p is a number of poles of the generator, φ is an internal power angle of the generator, ω is an electrical frequency, t is a time, αm, is a circumferential position angle of an air gap, MFs is a rotor magnetomotive force in normal condition and an air gap radial eccentricity fault and is generated by a permanent magnet, MFs is a stator magnetomotive force in normal condition and the air gap radial eccentricity fault and is generated by a stator winding, MFre1 is a rotor magnetomotive force in the air gap axial eccentricity fault and is generated by the permanent magnet, MFse1 is a stator magnetomotive force and is generated by the stator winding, and MFr1 is an amplitude of a 2nd frequency magnetomotive force generated by the permanent magnet with a rotation angle of −αm, under the stator inter-turn short circuit fault, MFr2 is an amplitude of 2nd frequency and 3rd frequency magnetomotive force generated by the permanent magnet under the stator inter-turn short circuit fault, MFs1+ and MFs1− are amplitudes of positive and negative rotation of the stator magnetomotive force under the stator inter-turn short circuit fault, MFs3+ is an amplitude of 3rd frequency of the stator magnetomotive force under the stator inter-turn short circuit fault;
a formula of a radial length of the air gap of the generator is as follows:
wherein g0 is an average length of the air gap under normal condition, αm, is the circumferential position angle of the air gap, and δs is a radial relative eccentricity of the air gap;
a permeability per unit area is inversely proportional to the radial length of the air gap and is expressed as the following formula:
wherein Λ0 is a permeability constant per unit area of the air gap, and μ0 is an air permeability;
the air gap magnetic flux density of the generator is obtained by multiplying the air gap magnetomotive force and an air gap permeance, and an expression of the air gap magnetic flux density of the generator under four working conditions is as follows:
calculating the root mean square value of the air gap magnetic flux density amplitude under normal condition, the air gap radial eccentricity, the air gap axial eccentricity, and the stator inter-turn short circuit fault by the above formula, wherein the expression is as follows:
wherein BN(rms), BR(rms), BA(rms), and Br(rms) are the root mean square value of the air gap magnetic flux density under normal condition, the root mean square value of the air gap magnetic flux density under the air gap radial eccentricity fault, the root mean square value of the air gap magnetic flux density under the air gap axial eccentricity fault and the root mean square value of the air gap magnetic flux density under the stator inter-turn short circuit fault, respectively; combined with a root mean square formula of the air gap magnetic flux density, calculating an eccentricity and short circuit degree by using a change of an air gap magnetic flux density amplitude, wherein the formula is as follows:

OG Complex Work Unit Math
wherein ϵ is the degree of air gap eccentricity, and fds is the degree of the stator inter-turn short circuit fault.