As an important part of renewable and clean energy, pumped storage power generation has been developing at a high rate in recent years. Due to the complexity and non-linearity of pumped storage power generation system, its operation may be affected by certain factors and become abnormal, resulting in poor power supply quality. The rotor winding inter-turn insulation (ITI) deterioration process is slow, and the early weak faults are not easy to detect in time is still a problem for the field operation and inspection. In order to avoid inter-turn short circuit (ITSC) faults leading to serious economic losses, this study proposes to use the positioning bar (PB) of pumped storage motors (PSMs) as a detection component, and its induced electromotive force (IEMF) can effectively react to the health level of rotor winding's ITI.
Firstly, the relationship between the stray flux and the main flux is derived by introducing the attenuation coefficient method, and then the characteristic harmonics of the PB's IEMF in ITSC state are obtained, according to which the harmonic amplitude ratio (HAR) threshold detection method is proposed. Secondly, a two-dimensional electromagnetic simulation model is constructed according to the operating parameters of PSM, and the evolution law of the IEMF's time/frequency domain characteristics before and after the ITSC fault are analyzed, as well as the validity of HAR threshold detection method is verified. Finally, combining with the signal conditioning device, the PB's IEMF information under different ITSC degrees in the dynamic simulation experimental generator are collected. Further calculating the HARs of multiple periodic signals, accordingly constructing a statistical box plot and setting the fault detection threshold, which can effectively provide guidance for the defense of ITI faults.
The simulation results show that the IEMF's time-domain peak value of PB decreases under normal, 2 turns-ITSC , and 4 turns-ITSC states. The corresponding IEMF's time-domain peaks are 6.74 mV, 6.3 mV, and 5.96 mV under no-load condition, while 7.33 mV, 6.72 mV, and 6.25 mV under load condition, respectively. Meanwhile, the frequency band 0 - 50 Hz of the PB's IEMF spectrum shows obvious fractional characteristic harmonics, and their amplitudes increase along with the fault level. Further calculating the fractional HAR, and according to the 5% elasticity margin, the fault detection thresholds under no-load/load conditions are set to 9.83% and 11.49%, respectively, which are 4.56% and 0.82% different from the minimum values of 14.39% and 12.31% in the 2 turns-ITSC state, so that the ITI defects can be identified accurately.
Experiments on the synchronous generator show that the peak time-domain values of the PB's IEMF corresponding to the faulty pole have a decreasing trend with the increase of ITSC degree. The peak values of the time domain corresponding to normal, 2.6%-ITSC, 5%-ITSC and 7.3%-ITSC under no-load condition are 120.07 mV, 115.43 mV, 112.24 mV and 109.05 mV, respectively, while those corresponding to normal, 2.4%-ITSC, 4.5%-ITSC and 6.6%-ITSC under load condition are 133.99 mV, 130.22 mV, 128.76 mV and 125.58 mV, respectively. Further analysing the PB's IEMF spectrum, there are obvious fractional characteristic harmonics in the frequency band of 0 - 50 Hz, and their amplitudes increase along with the ITSC degree, whereas the amplitude of 50 Hz fundamental frequency decreases slightly. In addition, the PB's IEMF information for 10 electrical cycles under no-load/load conditions are randomly selected for calculating the HARs, and according to the 5% elasticity margin, the fault detection thresholds under no-load/load conditions are set to 1.27% and 1.39%, which are 1.74% and 3.14% different from the minimum values of 3.01% and 4.53% in ITSC state, respectively. Therefore, the threshold method can be used to achieve the target defence of ITSC fault.
In this study, the HAR threshold detection method is proposed by deeply analyzing and mining the IEMF's time/frequency domain characteristic information of PB, and the validity is verified by the finite element modeling calculation of in-service PSM and the actual measurement of synchronous generator, which fills in the research gap of ITSC condition perception in the field of sensorless detection, and provides a new non-intrusive on-line monitoring method for the on-site operation and maintenance.
齐鹏, 李永刚, 马明晗. 抽水蓄能电机转子匝间短路无传感器检测方法研究[J]. 电工技术学报, 0, (): 9042-42.
Qi Peng, Li Yonggang, Ma Minghan. Study on Sensorless Detection Method of Rotor Inter-Turn Short Circuit in Pumped Storage Motors. Transactions of China Electrotechnical Society, 0, (): 9042-42.
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