The cause of the fluctuations in the motor stator temperature cannot be identified
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In December 2018, one of our company’s motors experienced fluctuations in stator temperature at two different points. On January 10, 2020, such fluctuations occurred at three different points, resulting in two instances of automatic shutdown due to interlocks. Upon on-site inspection, no loose connections were found in the motor’s junction box, the cable intermediate junction boxes, or the terminals in the cabinet room. An MTL safety barrier had been in use in the cabinet room for 9 years; there were no abnormalities in the cable shielding grounding or the resistance values relative to ground. At that time, the equipment was not started or stopped, and no adjustments were made to the frequency converter. After the equipment stopped operating, I checked it and found no problems; I turned the motor on again, and the temperature trend remained very stable with no fluctuations. I really can’t figure out why.:'( The curve shown in the attached image represents the temperature trend for December 2018, while another curve shows the trend for January 2020. It is the temperature that shows significant fluctuations, while the other curve represents the motor current
It’s a PT100, right? High-frequency vibrations can cause the solder joints of the PT100 to age and become loose, leading to temperature fluctuations; it is recommended to replace the temperature sensing probe
Moreover, interlocking based on the motor stator temperature is not recommended; how much does it cost to replace a burnt motor? How much is an unplanned stop? If that doesn’t work, use two out of two or three out of two
We have encountered cases where the wiring screws of the field thermocouples were loose, and the patterns on the DCS curves are very similar to yours.
The timeline makes it hard to see the ball clearly. The diagram isn’t very useful either. To infer the possible causes of a fault from a graph, at least a segment of the recording curve or data, measured in seconds, is needed – for example, data covering 2 minutes or 5 minutes. Otherwise, it’s all just random guessing. Who knows if Meng is right or not. . .
How do I replace the temperature sensor? Must only pre-installed spare probes be used? What if there is no backup?
I am from a manufacturer of temperature sensors. Some manufacturers encounter problems with the welding of PT100 elements, or the sealant at the front end of the sensor deteriorates over time, or the protection at that front end is inadequate allowing oil to get in. There is only one reason for temperature fluctuations; once external factors are ruled out, it must be that the resistance value of the thermistor has changed. A high-quality thermistor depends on proper welding techniques (the quality of the welding materials and the skill of the welder), adequate packaging at the front end to prevent oil from entering the sensor, and suitable cable materials (insulation properties and resistance to oil and heat are all important). In the production of temperature sensors, attention to detail is crucial
One of our clients in the coal chemical industry faced a problem that is quite similar to yours: their PT100 temperature would fluctuate and rise to around 100 degrees, which caused the system to shut down as well. You can send us the components so that we can simulate the operating conditions and conduct an analysis to determine whether there is a problem with the components. We can also go to the site and work together with you to identify the cause. It’s not possible to determine the exact temperature range from the pictures you provided; it’s necessary to find out exactly how much the temperature fluctuates and whether there is any pattern to these fluctuations. It’s best to consult a professional manufacturer to resolve this issue thoroughly.