How to determine the motor temperature and bearing temperature of a pump?

Use a thermometer to check, or touch it with your hand; generally, motors that are operating properly are not hot to the touch

The temperature measured at the bearing housing and bearing cover is usually 15%-25% lower than that of the outer ring of the bearing.

The API610 standard specifies the bearing temperature for pumps. Oil temperature and bearing outer ring temperature.

The requirement for an upper temperature limit is not used very often, but the requirement for temperature rise is often followed

1. AC motors for explosive environments: If these motors are used to drive high-speed oil pumps, such as 2-pole motors with speeds of over 2890 revolutions per minute, then since they operate in hazardous and explosive environments, inspectors must check them every half hour. The surface temperature of the motor should not exceed 85–90 degrees; due to the high speed at which these motors operate, their temperature should generally be kept below 80 degrees in summer. If this temperature is exceeded, the motor must be shut down (taking into account the insulation class of the motor’s windings).  The temperature of the bearings on the side of the motor can reach up to 80 degrees in summer. This depends on the type of grease used in the bearings: if it is lithium-based molybdenum disulfide grease, the temperature can go as high as around 85 degrees; whereas if it is calcium-based molybdenum disulfide grease, the maximum temperature is around 75 degrees. High temperatures can easily cause molybdenum disulfide to become liquid, losing its lubricating properties; a lack of oil in the bearings for just 10 minutes can lead to serious problems.    2. AC motors for non-explosion-proof environments on the ground: 4-pole and 6-pole motors. Due to their low speed, it is sufficient to lubricate the bearings regularly; the temperature should be maintained at 70 degrees. If the bearing temperature exceeds 80 degrees (in the case of motors with 4 poles or more), it is due to a lack of lubrication.  Measurement tool: Infrared handheld thermometer. Measurement locations: Surface of the motor (the temperature is highest near the suspension ring); motor bearings (surface of the side bearing covers). 3. DC motors: Since most DC motors are equipped with built-in cooling fans, the temperature is kept below 50 degrees; in summer, it does not exceed 60–65 degrees.

What I don’t understand now is whether the specified bearing or motor temperature refers to the surface temperature of the bearing or the internal temperature of the motor

This temperature increase is measured relative to the ambient temperature. When we talk about temperature, except in cases where sensors are installed directly at the bearing seats of large motors, it refers to the temperature of the motor’s bearing housing. If the ambient temperature is 20 degrees, and the temperature of the housing as measured is 40 degrees, then 40 degrees is the temperature that we measure and report; the temperature increase is therefore 20 degrees. Generally speaking, for motors, the temperature we measure should not exceed 120 degrees for long periods of time, as the lubricant cannot withstand such conditions.

I’d like to use this platform to discuss this with the experts here. The motor of our nitrogen pump is magnetic-type; sometimes its temperature rises to over 150 degrees, especially at low frequencies. However, once the frequency is increased, the situation returns to normal

Well, for example, if the ambient temperature is 40°C and I use an infrared thermometer to measure the temperature of the casing at the motor bearing area, which is 65°C, does that mean the temperature rise of the bearing relative to the ambient temperature is 25°C? Should we also consider the heat conduction of the casing? For example, if an additional 10℃ is added, is the actual temperature rise on the bearing surface considered to be 35℃?

High-precision infrared temperature sensing for temperature measurement