Monitoring the condition of large MV motors
In last month’s column, Rob Wood, ABB’s local business line manager for motors and generators, looked at predictive maintenance strategies for LV motors. This month, he examines what predictive maintenance means for larger motors.
Large motors and generators are often deployed in applications where process uptime is critical, and where, due to the size of the driven equipment, redundant capacity on site is limited. This means that if the machine stops, the whole process may be interrupted until the machine restarts, leading to costly downtime.
In addition to the financial implications, the knock-on effects of such a wide-reaching outage can take weeks, or even months, to overcome. When the stakes are this high, accurate condition monitoring is essential to prolong the machine lifetime and to make maintenance as time-efficient as possible.
On-line condition monitoring, performed while the machine is running, is essential because it allows the machine’s condition to be assessed without having to interrupt the process. Different machine parameters are collected either remotely or on site.
The raw data is analysed to get a clear picture of the machine’s condition in potential fault areas such as the cage rotor and bearings, or identifying issues with the cooler. An alarm is raised if the data is outside of normal operation parameters. Data can also be used to identify the underlying problem that caused the alarm, allowing maintenance to be planned accordingly. This makes on-line condition monitoring perfect for inaccessible machines in hard-to-reach areas such as offshore wind farms or marine applications.
Even with all of this on-line condition monitoring data available around the clock, there is still a need to inspect large machines physically, because some measurements can only be taken when the process is not running.
For instance, with high-powered motors and generators, the condition of the stator windings and the rotor bars needs to be monitored to avoid unplanned outages, and the best way to assess the physical condition of these is to inspect them visually. However, because most of the windings are sealed deep within the stator slots, the electrical condition of the winding insulation cannot be assessed visually. Parameters such as the dielectric strength of the insulation, and the presence of any voids or delamination within it, can only be determined by specialised testing.
For more information, you can watch this video: http://bit.ly/2Xloa9N
