TURNING GEAR MOTOR FAILURES, CONFIRMED BY MODEL BASED VOLTAGE & CURRENT METHOD

Abstract

This technical brief aims to showcase relevant information related to Model-Based Voltage and Current (MBVI) method. The paper discusses several fatal failures on the Turning Gear Motor (TGM) over the short time period of one-month, resulting in two motor replacements. The Turning Gear Motor was monitored by an online monitoring system using improved Motor Current Signature Analysis (MCSA), aka. Model-Based Voltage and Current (MBVI). TGM mechanical and electrical malfunctions are reflected in the dynamic current spectrum using improved MCSA. Utilizing this methodology, prompt and precise diagnostics was carried out and subsequent decision could take place regarding the electrical and mechanical integrity of this motor installed on this critical Centreline Machine Train. The paper further shows the real case data analysis and findings on this Electric Motor. The paper outlines the Expert Diagnostics System’s (based on MBVI) ability to distinguish automatically among different malfunctions. The Expert System uses the power spectral density (PSD) of the difference between the expected current obtained from the model and the actual current. These differences include only abnormalities generated by the motor anomaly. Therefore, they are immune to the noise or harmonics present in the supply voltages. MBVI is a suitable alternative or complimentary monitoring method, which does not require any sensor installation on the monitored equipment. All the measurements are carried out remotely in the motor control cabinet. The MBVI uses dynamic motor currents and spectrums to identify electrical, mechanical or process problems. MBVI is especially attractive for inaccessible motor driven equipment, particularly in this case, where the electric motor is located in the closed compartment of the Gas Turbine in the vicinity of the high temperature gases.