Jongwan Kim

Evaluation of the Influence of Rotor Magnetic Anisotropy on Condition Monitoring of Two-Pole Induction Motors

If nongrain-oriented rotor laminations are punched and stacked in a uniform direction, magnetic asymmetry is present in the rotor core due to the nonideal magnetic anisotropy. In this paper, it is shown that the influence of rotor core anisotropy can be misinterpreted as rotor faults in two-pole induction motors when performing motor current signature analysis. A detailed analysis of the influence of rotor core anisotropy shows that components produced by the rotor fault and rotor anisotropy interact, making reliable fault detection difficult. It is also shown that offline testing is currently the only available means of detecting the fault, and online monitoring of the space harmonics-induced current components is proposed as a viable solution for providing reliable rotor fault detection for two-pole motors with rotor anisotropy. The analysis and conclusions presented in this paper are verified through testing on custom-built lab motors and on 3.3-kV motors.

Power Spectrum-Based Detection of Induction Motor Rotor Faults for Immunity to False Alarms

It has recently been shown that spectrum analysis of instantaneous power can provide sensitive online detection of rotor faults in induction motors compared with current, torque, speed, or vibration spectrum analysis. However, it was reported that monitoring of the twice slip frequency, 2sfs, components induced by the fundamental component can produce false rotor fault alarms due to asymmetry in the rotor or low frequency load oscillations. In this paper, the rotor fault components induced in the power spectrum by the stator fifth and seventh space harmonics are derived to evaluate their immunity to false alarms. It is shown that the (6 - 8s)fs component can provide reliable detection of rotor faults under cases where existing methods produce false alarms. An experimental study performed on custom built rotor samples shows that the new components are capable of detecting rotor faults immune to false alarms produced by rotor axial air ducts, rotor anisotropy, and low frequency load oscillations for cases where existing methods fail. The components derived in this paper can also be applied to vibration, speed, torque, or acoustic monitoring for reliable detection of rotor faults.

Experimental Evaluation of Low-Voltage Offline Testing for Induction Motor Rotor Fault Diagnostics

The offline single-phase rotor rotation test is frequently used in the field for assessing the integrity of the rotor cage without motor disassembly. However, the inconvenience of the large variable voltage supply requirement has triggered the advent of a portable low-voltage version of the test also known as the rotor influence check. This test has recently become common in the pulp and paper industry as it is convenient to use in an industrial environment. However, concerns on the reliability of the test have been raised due to frequent false test indications. The objective of this work is to provide an analysis and experimental evaluation of low-voltage rotor tests under controlled rotor fault conditions on 380-V and 6.6-kV motors. The results of the low-voltage test reveal that it cannot provide reliable diagnosis due to the low excitation flux level, particularly for motors with the closed rotor slot design. The single-phase rotation test and online current spectrum analysis are also performed under identical fault conditions to show that the fault conditions can be detected with standard tests.

Evaluation of the influence of rotor magnetic anisotropy on condition monitoring of 2 pole induction motors

Non grain-oriented silicon steel laminations used in electric machines show a small degree of non-ideal magnetic anisotropy, which is introduced during the rolling process. If the rotor laminations are punched and stacked in a uniform direction, magnetic asymmetry is present in the rotor core. In this paper, it is shown that rotor core anisotropy can produce twice slip-frequency, 2sfs, modulation that can be misinterpreted as rotor faults in 2 pole induction motors when performing motor current signature analysis (MCSA). Unnecessary motor inspection due to false rotor fault alarms is a common on-going problem in the field, and it is shown for the first time in this work that rotor anisotropy is a root cause of false MCSA alarms in 2 pole induction motors. The influence of rotor core anisotropy is analyzed in detail, and it is shown that 2sfs components produced by the rotor fault and rotor anisotropy interact, making reliable fault detection difficult with MCSA. It is also shown that off-line testing is currently the only available means of detecting the fault, and on-line monitoring of the space harmonics-induced current components is proposed as a viable solution for providing reliable rotor fault detection for 2 pole motors with rotor anisotropy. The analysis and conclusions presented in this paper are verified through testing on custom built lab motors and on 3.3 kV motors.

Enhancement of biodegradability of EDTA by gamma-ray treatment

Radiation treatment with gamma-rays was used to improve the biodegradability of EDTA that is known to be a non-biodegradable substance. The effect of metal ions and catalysts on the treatment of EDTA was studied first. The removal of EDTA was definitely decreased in the presence of metal ions such as Cr(III), Cd(II), Pb(II) and Cu(II) at doses greater than 3 kGy. The addition of a TiO2

Active and Reactive Power Spectra-Based Detection and Separation of Rotor Faults and Low-Frequency Load Torque Oscillations

Motor current signature analysis (MCSA) based detection of rotor cage faults (RFs) in medium-high voltage induction motors has become common in the field due to its low-cost remote monitoring capability. However, low-frequency load oscillations (LOs) in applications that employ speed reduction couplings can induce frequency components in the vicinity of that of RFs. It has been reported that false-positive or -negative RF indications can be produced with the MCSA, if the frequency components produced by RF and LO overlap. There, recently, have been studies on discriminating RF and LO; however, the case where two harmonic components overlap at the same frequency, which is the most difficult and serious case, has not been investigated. In this paper, a spectrum analysis of instantaneous active and reactive power is applied, and it is shown that RF and LO can be separated for the case where the MCSA fails due to the overlap in the two spectral components. An experimental study performed on a 380 V motor with a speed reduction gear shows that RF and LO can be reliably detected and separated for avoiding false RF indications.