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What is the first step to check for motor bearing heating?

Date:2023-08-15   Author:XINDA MOTOR
What is the first step to check for motor bearing heating?

    We have been asking ourselves a question, why is the problem of motor bearings a problem that many engineers hope to solve, but everyone has not systematically studied the application technology of motor bearings? Later, I found that all the previous technical introductions started from the knowledge itself, which was indeed good in terms of system, but from the perspective of "emergency", it made the engineers a little anxious. The motor is broken there, how can the engineers have the time to systematically learn from scratch?

     So from another perspective, starting from the motor failure, we will sort out the motor bearing problems and corresponding knowledge, which may meet everyone's short, flat and fast requirements.

     So I am here to sort out the knowledge of motor bearing application technology from the perspective of motor bearing failure. But it must be explained that due to space and other issues, many things here are more popular science, and there is no way to expand them in depth.

     Speaking of motor bearing failures, vibration, noise and heat are the two major themes. Here we only talk about the problem of heat generation, and the problem of vibration and noise will be another topic.

     Electrical engineers often ask me how to deal with the overheating of motor bearings. For electrical engineers, heating is a phenomenon, and there are many knowledge points behind it. In the past, I always asked many questions repeatedly after receiving questions before I could come to a judgment. In fact, engineers may not know how many knowledge points and interconnections are involved behind a sentence of fever. A few days ago I tried to do a comb, as shown below:

 Let's start from the beginning. Once the motor heats up, the engineer's first action is to understand where the heat is generated. The main component of the motor system is the search target. Therefore, we need to know the possible hot spots or the measured hot spots in the first place. These include:

- base temperature is too high;

- shaft temperature is too high;

- excessive temperature near the seal;

- Bearing temperature too high.

     Of course, the temperature therein is detected accordingly. The usual measurements are obtained through embedded thermometers, or by on-site measurement. So before talking about fever, make sure the measurement is correct. This is also the first step in diagnosing motor heating problems. The site engineer must determine:

- Whether the embedding of the temperature measuring element is reliable;

- Whether the connection of the temperature measuring element is reliable;

- Whether the temperature measurement position is appropriate;

- Whether there is any unnecessary heat source interference near the temperature measurement point.

Temperature measurement position

     Regarding the bearing part, what needs to be emphasized is the temperature measurement position. Usually what we refer to as the motor bearing temperature refers to the temperature of the outer ring of the motor bearing. In motor manufacturing, a thermometer may be embedded, and the embedding position should be as close as possible to the outer ring of the motor bearing. The data measured in this way is closer to the motor bearing temperature that needs to be provided.

Bearing temperature

     In engineering practice, I have also encountered situations where electrical engineers mistakenly consider the motor insulation temperature level as the bearing temperature.

     For example, someone once asked me about Class B insulation, hoping to choose bearings according to the temperature of 120 degrees. This is unreasonable. Because the insulation grade temperature of the motor refers to the temperature of the winding part of the motor. The insulation of the winding needs to ensure the insulation effect at this temperature. After the winding heats up, it is transmitted to the bearing through the end cover of the machine base or the shaft, and the heat will be dissipated, so the temperature will be greatly reduced. Therefore, this temperature cannot be used to make requirements for the bearing.

environmental impact

     The measurement of motor bearing heating is also affected by the environment. The temperature of the same motor and the same load will be different under different ambient temperatures. Therefore, when the temperature of the motor in a certain working condition in a certain place in Guangdong is higher than that in Harbin, it does not mean that there is a problem with the motor. There is another example. I once worked as a guide in an Indian motor factory, and they strongly demanded that high-temperature grease be used as standard grease. Before I went to India, I felt that this request was not based enough, but when I arrived there, I found that their request was in line with the local reality. But at the same time I will warn the other party that if your motor is exported to the north, the grease must be adjusted.

     The same case also appeared in China. A motor factory in China produced motors for snowplows in Russia, and the problem of bearing burnt occurred in a large area in Russia. In fact, the requirements of the ambient temperature for lubrication are not considered. The grease cannot form lubrication at low temperature, but has side effects, resulting in insufficient lubrication and burning of the bearing. Before the failure of the bearing, it was burned at high temperature, but the time was very short, and it was not noticed by the on-site engineers, let alone a time window for solving the problem. This is a typical problem of "bearing overheating" burning in a "low temperature" environment.