Identification of false rotor fault indications produced by on-line MCSA for medium voltage induction machines

Abstract

Motor current signature analysis (MCSA) has become an essential part of the preventive maintenance program for monitoring the condition of the rotor cage in medium voltage induction motors in the pulp and paper industry. However, many cases of false indications due to interference from the motor or load have been reported. False indications can result in unnecessary inspection and outage costs (false positives) or major repair/replacement costs and loss of production (false negatives). The objective of this paper is to present the potential root causes of false indications, and provide guidelines on how commercially available off-line and on-line tests can be applied for identifying false indications from a field engineers' perspective. Case studies of false MCSA indications and results of alternative commercial tests forimproving the reliability of the diagnosis are provided through measurements on 6.6 kV and laboratory motor samples. Finally, new test methods under research and development for reliable rotor fault detection are summarized and unresolved problems are listed. This paper is expected to help field maintenance engineers prevent unnecessary motor inspection and forced outages, and guide researchers target future research towards industrial needs.

Influence of Blade Pass Frequency Vibrations on MCSA-Based Rotor Fault Detection of Induction Motors

“…From (6), it can be seen that a rotor fault produces a stator current vector, , , that rotates in the direction of rotor rotation (positive (+) sequence) at fRF=(1-2s)fs, and BPF vibration induces a vector, , , that rotates in the opposite direction (negative (-) sequence) at the same frequency. The relative direction of rotation between the , and , vectors are illustrated in Fig.…”

“…There recently has been active research on timefrequency analysis of the startup current for rotor fault detection due to its performance and reliability benefits. The improved sensitivity of fault detection due to the large rotor current under startup, and its immunity to false indications have been reported in [6], [13], [20], [32]- [33].…”

Induction Motor Diagnostic System Based on Electrical Detection Method and Fuzzy Algorithm

“…For mixed eccentricity, both the cylinder and the center of rotation are displaced from their respective original positions [22]. The frequencies of these components are given by (8).…”

“…Therefore, this paper uses the electrical detection method to analyze rotor and eccentric faults of a motor and assess the operating state of the motor with such faults [1,2]. Motor current signature analysis (MCSA) is currently one of the most popular techniques for monitoring the condition of medium-voltage induction motors online in an industrial environment [3][4][5][6][7][8]. When a fault occurs, the magnetic flux changes.…”

Influence of blade pass frequency vibrations on MCSA-based rotor fault detection of induction motors

“…the fBPF and fRF frequencies are identical with opposite signs at the frequency shown in (6), if k1Nb/P is equal to 1 (for k2=1). From (6), it can be seen that a rotor fault produces a stator current vector, , , that rotates in the direction of rotor rotation (positive (+) sequence) at fRF=(1-2s)fs, and BPF vibration induces a vector, , , that rotates in the opposite direction (negative (-) sequence) at the same frequency. The relative direction of rotation between the , and , vectors are illustrated in Fig.…”