Analysis On Torque Characteristics Of Generator Under Air-Gap Eccentricity And Stator Short Circuit Composite Faults

Air-gap eccentricity and stator inter-turn short circuit(SISC) are common faults of generator, which produce harmful effects on the normal operation. This paper is aimed at the investigation on the characteristics of generator’s electromagnetic torque(EMT) when static air-gap eccentricity(SAE) and SISC composite fault(CF) occurs,and the EMT characteristics includes the frequency components and amplitude variation of each component, as well as features of mean, RMS.Analytical derivation, computer simulation and dynamic test on generator set are the research methods of the paper. Firstly, the relationship between air-gap permeance,magnetic motive force and influence factors is derivated. Hence, the expression of air-gap magnetic energy is obtained from the former relationship, and the EMT expression, which explains the effection of related fault factors on EMT, is derivated on the strength of principle of virtual displacement. Therefore, qualitative analysis of the frequency components and amplitude variation of each component are carried out.Secondly, simulation models of MJF-30-6 generator with SAE and SISC faults are founded and calculated by Ansoft Maxwell, a computer sofeware aimed at simulation of electromagnetic field. The simulation result contributes the quantitative analysis of EMT characteristics and different fault types and different fault degrees. Lastly, the MJF-30-6 generator is tested to acquire signals under different SISC locations and different fault degrees. And the EMT variation with SISC fault is obtained from the signals, which verifies the EMT characteristics obtained from the analytical derivation and the computer simulation.The analysis shows that: the electromagnetic torque of the composite fault is different from the single falults. Firstly, SAE increases the EMT mean and second harmonic amplitude while SISC decreases the EMT mean and RMS, as well as SISC increases the EMT even harmonic amplitudes. Secondly, the EMT characteristics in SAE and SISC composite fault condition are related with fault degree and relative fault location. For the fault degree, SAE increases the mean, RMS and even harmonic amplitudes, as well as SISC decreases mean and RMS and increases even harmonic amplitudes. For the relative fault location, the EMT mean and RMS are decreased while the even harmonic amplitudes are increased due to the smaller circumferentialangle between the situation of SISC winding and the location of minimum air-gap.The EMT variation shows the correspondence relationship between the generator EMT and composite fault(CF) factors, and it provides a new reference basis for the monitoring and diagnosis at air-gap eccentricity and stator short circuit composite fault of the generators in actual production.