High motor temperature

If the temperature of the motor is abnormal, it is possible to check whether there is a missing phase in the motor’s power supply. This involves various checks, primarily focusing on the contacts of the contactor. A missing phase in the motor can cause its temperature to rise excessively; if this persists for too long, it may even lead to the motor being damaged； Listen again to see if there are any abnormalities in the sound of the motor’s operation; abnormal sounds may indicate damaged bearings, which should be replaced. For a motor, these two aspects are the main things to check.

If the motor temperature is too high, it is usually due to some issue with the mechanical load; an excessive load can easily cause the motor’s temperature to rise.

The motor’s temperature is abnormal; I’m not sure if the original poster has taken any actual measurements. If one relies on touch alone, for an F-class insulation, the temperature rise should not exceed 80°C, and considering the ambient temperature, a surface temperature of around 90 degrees is quite normal. With B-class insulation, a surface temperature of around 60 degrees is also normal, but it will still feel hot to the touch. Therefore, it would be best for the original poster to first determine whether there is indeed an abnormal temperature, and then identify the cause.

A high motor temperature can be caused, firstly, by overload of the motor; secondly, by whether the voltage applied to the motor is within the specified range; and thirdly, by an excessively high ambient temperature.

Is the three-phase current balanced?； Motor cooling condition ； Phase loss ； overload ； Mechanical reasons (such as bearings)

For induction motors driven by frequency converters, in situations where they operate with frequent forward and reverse rotations, another possible cause of high motor temperature rise is the low power factor at low speeds, which leads to high current flows over extended periods of time. The usual solution is: 1. Improve the identification accuracy of the motor mathematical model ； 2. Implement the torque enhancement function in the low-speed range.

Actual temperature, bearings, three-phase voltage, three-phase current, load

It is necessary to check whether the ventilation is working properly; if the fan has fallen off or the air ducts are blocked, the motor will get very hot

First, check whether there is a phase loss; next, see if the rotor is stuck (the load might be too high)… or it could be friction between the coil and the casing, though this possibility is relatively low!

It is necessary to check the current, voltage, coils, bearings, etc. to determine the cause.

:D 1) Reasons for motor overheating due to power supply issues: There are several reasons why the motor overheats as a result of problems with the power supply: a) Excessively high supply voltage – When the supply voltage is too high, the back EMF of the motor, as well as the flux and flux density, increase accordingly. Since the magnitude of iron loss is proportional to the square of the magnetic flux density, an increase in iron loss leads to overheating of the core. An increase in flux, in turn, causes a sharp rise in the excitation current component, resulting in increased copper losses in the stator windings and leading to winding overheating. Therefore, when the supply voltage exceeds the motor’s rated voltage, it causes the motor to overheat. b. Low supply voltage: When the supply voltage is too low, if the electromagnetic torque of the motor remains constant, the flux will decrease. As a result, the rotor current increases, and the component of the stator current related to the load also increases. This leads to increased copper losses in the windings, causing the stator and rotor windings to overheat. c. Unsymmetrical supply voltage: When one phase of the power supply cable is broken, a fuse in one phase blows, or the contacts of the starting device get damaged causing one phase to be disconnected, this will result in the three-phase motor operating on only one phase. As a consequence, the two phases that are in operation experience high currents, which leads to overheating and eventual burnout. d. Unbalanced three-phase power supply: When the three-phase power supply is unbalanced, it causes the currents in the motor’s three phases to be unbalanced, leading to overheating of the windings. As can be seen from the above, when a motor overheats, the power supply should be considered first. After confirming that there are no issues with the power supply, consider other factors. 2) Reasons why load causes the motor to overheat. The reasons for overheating of the motor due to load include the following: a. Overloaded operation of the motor. When the equipment is not properly matched and the load power on the motor exceeds its rated power, the motor operates under overload conditions for an extended period of time (in other words, trying to pull a heavy load with a weak motor), which leads to overheating of the motor. When repairing an overheating motor, it is necessary to first determine whether the load power matches the motor’s power, in order to avoid unnecessary disassembly. b. The mechanical load being pulled does not operate properly. Although the equipment is complete, the mechanical load it pulls does not function correctly; the load varies in magnitude during operation. For example, when too much material is fed into the thresher, the motor becomes overloaded and heats up. c. Fault in the machine being pulled: If the machine being pulled has a fault, such as inflexible rotation or getting stuck, it will cause the motor to overload, leading to overheating of the motor windings. Therefore, when troubleshooting motor overheating, load-related factors cannot be ignored. 3) Reasons for overheating caused by the motor itself: There are several reasons for overheating resulting from the motor itself: a. Open circuit in the motor windings – When one of the phases in the motor windings is open circuit, or when one of the parallel branches is open circuit, it will lead to an imbalance in the three-phase currents, causing the motor to overheat. b. Short circuit in the motor windings: When a short circuit occurs in the motor windings, the short-circuit current is much higher than the normal operating current, which increases the copper losses in the windings, leading to overheating and even burnout of the windings. c. Incorrect motor wiring: When a motor connected in a delta configuration is connected in a star configuration by mistake, it continues to operate under full load. The current flowing through the stator windings exceeds the rated current, which can cause the motor to stop running on its own. If it remains stopped for an extended period without the power supply being disconnected, the windings will not only overheat severely but may also get burned out. When a star-connected motor is connected in a delta configuration, or when motors whose coil groups are connected in series to form one circuit are connected in parallel across two circuits, it will cause the windings and core to overheat; in severe cases, the windings may be damaged. e. Incorrect motor wiring: When a coil, set of coils, or phase winding is connected in the wrong direction, it can lead to severe imbalance in the three-phase currents, causing the windings to overheat. f. Mechanical faults of the motor: When the motor shaft is bent, the assembly is improper, or there are problems with the bearings, it can lead to an increase in the motor current. This increases copper loss and mechanical friction losses, causing the motor to overheat. 4) Reasons why poor ventilation and heat dissipation cause the motor to overheat. The reasons for overheating of the motor due to poor ventilation and heat dissipation are as follows: a) High ambient temperature, which results in high inlet air temperature. b. Debris blocking the air inlet prevents proper airflow, resulting in a low volume of air intake. c. Excessive dust inside the motor hinders heat dissipation. d. The fan is damaged or installed incorrectly, leading to no airflow or a low volume of airflow. e. No air shroud is installed, or there are no baffles inside the motor’s end cover, which prevents the motor from having an adequate air flow path

Mainly considering mechanical and electrical aspects, (1) whether the motor shaft is damaged. (2) Whether the load is outside the range. (3) Is the voltage normal (phase loss, under-voltage, over-voltage)?

Is the ambient temperature high as well? Is the ventilation good?

Based on my experience, check the bearing shells.

High motor temperature: 1. Check whether there is a missing phase in the motor’s power supply, and whether the contacts of the contactor are not making proper contact； 2. Is there any abnormality in the sound? Abnormal sounds may be caused by damaged bearings in the motor, and the bearings should be replaced ； 3. Is it operating under overload? ； 4. Whether the cooling fan is damaged, etc

The temperature rise under rated load exceeds the values specified on the nameplate. In any case, it constitutes a fault and the machine must be stopped for inspection; special attention should be paid to sudden increases in temperature rise. The external causes include: too low grid voltage or excessive line voltage drop (over 10%), excessive load (over 10%), and improper coordination between the motor and the machinery. Internal causes include: single-phase operation, inter-turn short circuits, phase-to-phase short circuits, stator grounding, damaged or loose fans, blocked air ducts, damaged bearings, rubbing between the stator and rotor, overheating at the connections between the motor and cables, especially in copper-aluminum or aluminum-aluminum connections, as well as corrosion or moisture damage to the motor. Furthermore, in theory, motors can rotate in both directions, but the fans of some motors have a specific direction; if this direction is reversed, the temperature rise will be significantly higher.

** Will the current change in the case of a missing phase?