INFRARED THERMAL IMAGING
By: Chuck Peterson
Owner Peterson Predictive maintenance
How is INFRARED THERMAL IMAGING used in the work place?
- Electrical Inspections
- Mechanical Inspections
- Energy Conservation Programs
- Building Diagnostics
Electric motors should have a band around the center of the motor that is warmer than any other part of that motor. Once the motor is up to running speed then the rotor rises to magnetic center, it also move axially to the magnetic center. At that point the rotor and the bearings are actually floating if you will. They are essentially unloaded. There should be no heat there from friction and they should be cooler than the center of the motor or the band that we are looking for.
Notice the center of the motor is showing the heat band that we are looking for. The outboard and the inboard bearings are both cooler than the center of the motor. If either one of these bearings shows hotter than the center of the motor, we have a bearing problem. We do not know yet what that problem is but we do know we have a problem.
The problem could be;
- Dry needing grease
- Belts pulled too tight
- Shaft to Shaft misalignment
Or it could be any one of several potential problems, this is the first indicator of a problem arising.
- Motor Control Centers (MCCs)
Motor control centers are unique in that they have several different potential problems. Loose wire connections seem to be the most often incurred problem. The wire when energized heats up and expands or swells some, when it is de-energized it then cools back down and contracts back to it's smaller state. Infrared Thermal Imaging allows us to see the heat that is built up at those loose connections. It takes more power to jump across
that gap therefore more heat at that point.
Notice the C phase wire connection in the image above. It show hotter than the wire either side of it. The same load coming from the same source to the same machine, they should be nearly the same.
Again the center wire is showing hotter that the outside ones. Also notice how the wire seems to cool off as it get farther away from the connection. This usually indicates a loose connection at the hottest point.
These connections need to be pulled and cleaned then reinstalled making sure that all wire connections are tight.
Fuse clips will start to lose their spring tension at approximately 200°. When this happens the fuses get loose and then we have a gap in the fuse clip. be it ever so small it still takes more power to jump across that gap. The more power the more heat. Once these clips have lost that tension they can not be repaired, and should be replaced. Some of the highest heat and the most potential for melt down is found in problems with fuse clips.
Notice the A phase fuse clip in the image above. This is a bad connections and will only get worse until the problem is resolved.
As can be seen in the above images, there is potential for some real problems here. We can not see these problem developing with our own eyes, thus INFRAED THERMAL IMAGING extends our sense of sight to enable us to see the problem so it can be corrected before it becomes a real problem.
Power Distribution Centers
This is where when something goes wrong it can be catastrophic and cause hundreds of thousand of dollars in major damage. The bad thing here is that when it happens it usually takes several other components out within it adding to the cost of repairs and to the down time while making those repairs.
These could include;
- Line Capacitors
- Line fuses
- Line side and load side of Transformers
- Buss bars (Overhead and in Switch gear)
Most of the problems we find in this type equipment are in the switching equipment. Ether on or off switching or fuses. The dip switches set out in the weather all the time and gather dust and corrosive materials. Thus they start to corrode. This corrosion builds up resistance and resistance causes heat. These are seldom ever checked and in fact never dealt with unless there is a problem and most often they are the problem.
Notice the cut out switches in the image above. We are not sure of the temperature of these switches but it doesn't take a rocket scientist to tell that there is a potential problem here. A melt down in these switches shuts down the entire plant, the down time alone would be astronomical in costs.
Here again we see all three phases are showing heat from looseness and corrosion. This was to a plant that makes in the neighborhood of $250,000 a day profit. There is no question about what it would cost to be shut down for a week while damages from a melt down were fixed. What about the collateral damage that occurs when this go out. The costs just keep piling up.
We have a real potential problem here in this metering station. Again a melt down here would be very expensive, but these systems are seldom ever checked.
Here we have the potential for a major problem. This is the load side of a very large transformer. Notice the B phase is hotter that the A phase and the C phase. With the heat showing on this cone as it is this indicates that the problem is on the inside of the tank. The heat is conducting to the outside. Notice the wire connections and appear to be clean and tight. This also indicates that the heat source is inside this transformer. This problem is not going to go away. These kind of problems do not heal themselves.
Smaller transformer with single conductor wire can also cause problems. We have a lot of these in small substations that power the small towns out in the rural areas. If one of the $1.25 connectors melts down it blacks out the entire city. These should be checked on an annual basis.
Overhead buss bars are a real problem that we can not see with our eyes and we are never up there to check them. Vibration from truck and trains and forklifts work the butt splices in the bars loose and then we have heat building up. No one ever gets up there and checks these connections, INFRARED THERMAL IMAGING allows us to check from the ground.
Shaft to Shaft
Shaft to Shaft misalignment is the second leading cause of premature motor failure. The stress that is placed on the inboard bearings from a direct misalignment severely shortens the life of that machine. With INFRARED THERMAL IMAGING we can see the heat from that stress and sometimes we can even see the heat build up in the coupler.
Notice the heat build up on the two inboard bearings. This is one of the first indicators of possible misalignment.
Here we see the rubber in the center of this Martin style coupler heating up from being worked back and forth by the hubs that are severely misaligned. Notice the heat in the inboard motor bearing and on the shaft of the pump.
Pulley to Pulley Alignment
This alignment is most often overlooked and left to a straightedge to align the pulleys. This not only places undue stress on the bearings but will ruin the v-belts in a very short time. Usually you will see the powder from the belts rubbing the pulleys and wearing off, this severely shortens the life of both the belts and the machines. These should always be laser aligned if for nothing else but to save on the matched sets of belts.
This is a single belt drive that is obviously misaligned. Notice the heat that is placed in each pulley because the belt is not running true. This is a simple alignment that should be completed every time the belt is changed. You can see in the image that this one was just tightened up and turned on.
Notice the heat from the belts slipping on the pulleys on this gearbox and motor.
This could easily be corrected with a proper alignment.
When it comes to shortening the life of a bearing heat is the biggest problem we have. The main reason for grease is to lesson the friction between the rolling element and the race thus causing less heat to build up. Here we must also address the subject of over greasing. there is more damage done to bearings by over greasing than there would be if we did not grease them at all. Over greasing builds up the old grease and then it becomes an insulator and holds the heat in the bearing causing more damage.
Notice the leaking around the end bell on this motor. This is the first indication that a motor has been over greased. Then it starts to heat up, so what do we do, we grease it again.
Motor bearings should be greased by Ultrasound and using a grease made specifically for those motors and their speeds. All purpose grease is for the farm, not for the manufacturing plant.
The image above is a pillow block bearing that is heating up. This could be caused by the belts being too tight, or by being dry, or by misalignment or a combination of all of the above.
Pressure Relief Valves
As we can see this Pressure relief valve is holding just fine. If it were leaking by the discharge pipe in the front of the image would be hot from the heated water and steam escaping through the leaking valve.