Prevention of outage major downtime

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Courtesy of Sulzer Management Ltd

Sulzer Dowding & Mills uses a range of condition-monitoring methods to assess the status of motors and generators to prevent the customer from major downtime and lost production.

One of the most common root causes of failure of rotating electrical machines is bearing failure; but the failure mode that has the greatest impact, with regards to downtime and lost production, is failure of the stator winding insulation, particularly in highvoltage machines. Premature failure of stator insulation can cause a costly, forced outage. Therefore, prevention of such outages is a major objective. To this end, there has been a lot of effort put toward developing reliable insulation quality assessment techniques. Sulzer Dowding & Mills uses a range of condition monitoring methods, partial discharge analysis (PD), phase current analysis, insulation resistance (IR), polarization index (PI), tan delta analysis, and most importantly, close visual inspection to assess the status of the winding insulation and bearing system. Vibration analysis is used to assess the condition of the bearings and rotating parts of the machine, whilst thermographic cameras are used to identify variations in heat that result from bearing problems, bad electrical connections, unbalance in phase loadings, etc.

Parameters routinely monitored either periodically or online—include vibration, temperature, partial discharge, and, occasionally, shaft voltage. This data together with operating data such as load, running hours, ambient and environmental conditions, system disturbances, etc., are used for condition assessment of the entire machine.

Analysis of mechanical vibrations
Analysis of the measured mechanical vibration is an excellent method to indicate the current condition of a machine—even where the vibration levels are not necessarily at high levels. They provide an indication of the machine condition because they reflect the dynamic forces acting on the rotating assembly in service, and with good analysis can be used for the early detection of abnormalities and trouble.

High vibration, in addition to causing bearing overheating and, ultimately, bearing failure, can also cause damage to winding insulation systems in rotor and stator. All of these conditions require extensive out-of-service repairs. A modern vibration monitor system

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