Electrical PM & PdM Engineer
In modern industries, there are many predictive maintenance techniques that can be utilized to avoid an unexpected failure. At CEMEX, we count on those techniques and deploy them in such a way as to get the most use from it, and avoid any undesirable consequences. IR thermography's use has become widespread in cement plants; application areas typically include rotating kilns, insulation, mechanical, and electrical systems.
This article will explore the uses of IR thermography, specifically as part of the Motor Control Center systems predictive maintenance routine, including typical electrical panel failure points (contactor, terminations, feeding breaker, fuses, cables, etc...).
One of the Clinker Rotary Kilns (4,500 Tons per Day) is supposed to be available for operation not less than a year, which is a challenge of course, to guarantee continuous operation for the kiln system for this time without any unexpected shutdown.
If we take a close look inside the variable speed drive panel, many failure points (marked in Fig. 3) could put the kiln operation at risk if a loose contact or degradation occurred in one of the electrical components. Because we are dealing with equipment in operation, and with regard to the safety aspects of live work, we incorporate one of the most useful tools available for the PdM team, our IR camera. The camera can easily detect problems associated with heat transfer through a “live” IR inspection on operational electrical systems.
During our bi monthly IR inspections, according to the predictive maintenance schedule, and thanks to our IR camera (FLIR P640) and ThermaCAM Reporter, we found high heat radiation from one of the main contactors in the DC drive feeding Kiln 02 Main Drives as shown in Fig.4 and 5.
|Atmospheric Temperature||31.3 °C|
|Ar1 Max. Temperature||88.1 °C|
|Ar1 Max. Temperature||48.2 °C|
Figure 6. Analysis TableThe following parameters were used as references to analyze the thermography results:
- Feeding voltage and current.
- Field and Framework voltage.
- Field and Framework current.
- Motor speed.
- Load percent.
So we cannot just tell the responsible coordinator to check the bolt tightness and the condition of the connection components, the internal contacts should be checked because it consists of two parts (fixed & moving) contacts, of course we cannot see inside due to the low emissivity protective fiber cover in front of the contacts.
The heating in electric equipment is an indicator of its operative state, they have normal heating produced by the electric current flow and they also have abnormal heating produced by equipment conditions that increase the resistance to current passage and increases the heat generation in those points. In our case the contact condition was abnormal due to the internal mechanism which needed to be maintained.
But the area coordinator asked me why I did not find this problem earlier since I scan this contactor every two months. I told him that the temperature difference between one and another case can be minimal in incipient problems, and it will increase when the problem becomes bigger. As our perception capability of hot spots is limited to high temperature levels, we cannot always detect abnormal heating problems from their beginnings. Fortunately, by carefully studying the inspected equipment, we can figure out the best routes and inspection frequencies. By good planning, downtime was minimized to the max.
Figure 10 illustrates the temperature pattern after the repair.
|Atmospheric Temperature||33.5 °C|
|Ar1 Max. Temperature||44.7 °C|
|Ar2 Max. Temperature||44.0 °C|
Figure10. IR image for the new contactor after operation for a week
By the early detection of the high heat radiation and imbalance found using our best technology on the Predictive maintenance team, many undesired scenarios were avoided:
- Damage to the entire contactor.
- Damage to the other adjacent electrical components in the variable speed drive.
- Emergency kiln stop for not less than 10 hours.
- Losing about 2500 Tons of clinker ($306,000 USD).
It has to be mentioned that thermography reporting and feedback should be accurate and hit the problem in order to take the right corrective actions and to solve the problem completely without any unlikely consequences.
Only one hour of stoppage and losing about 188 tons of clinker ($23,000 USD) , was the only cost paid in this regard.
Ahmed earns 11 ITC certification renewal credits for his article.