Measures to Control Motor Temperature Rise and Ensure Safe Operation

Measures to Control Motor Temperature Rise

The temperature rise of the motor stator windings is positively correlated with the current. As the current increases, the temperature rise naturally increases, and the rate of increase is even more significant. Apart from the effect of the current, temperature rise is also influenced by other factors such as fluctuations during the manufacturing process and quality control. To avoid non-compliance due to such fluctuations, a certain margin should be left in the product design.

The technical specifications for the motor will define the rated voltage and frequency range. If the motor operates outside this range, it will fail to work properly. Therefore, it is essential to ensure that the electrical grid parameters meet the motor’s normal operating conditions. The most direct factor is the impact of voltage on the motor windings. In particular, temporary outdoor wiring often uses aluminum core cables for cost and material safety reasons. This can result in a significant voltage drop applied to the motor. When this happens, the motor will draw excessive current, which can cause severe overheating and eventually lead to motor failure due to overheating.

When the motor's temperature rise does not meet standards, there are limited remedial measures. We can control the temperature rise by increasing the number of varnish impregnation cycles, enlarging the fan width and outer diameter, or reducing the rotor diameter to increase the air gap, though these actions may compromise other motor performance. Increasing the air gap can be effective for 2-pole motors as it reduces stray losses and weakens the heat radiation from the rotor to the stator. However, this may not be effective for multi-pole motors as it could lead to a significant increase in excitation current.

For motors with lower slot fill factors, increasing the varnish impregnation cycles or using vacuum pressure impregnation can improve the heat conduction between the winding slots and the stator core. However, excessive varnish buildup at the winding ends may hinder heat dissipation. Additionally, the varnish layer on the external part of the winding can prevent varnish from penetrating inside the winding during subsequent impregnation, reducing its effectiveness in controlling temperature rise.

When conditions allow or when necessary, adjusting the electromagnetic parameters can effectively control temperature rise. For example, reducing the number of winding turns per slot in the stator or increasing the wire diameter can reduce electromagnetic load and wire current density, which is highly effective in lowering temperature rise. Particularly for enclosed motors, reducing the number of winding turns in the stator reduces both stator and rotor copper losses. Although iron losses may increase, the stator core dissipates heat more easily than the winding. Another issue to consider is that reducing the number of winding turns may lower the power factor and increase the starting current, which could require increasing the core length or modifying the rotor slot shape to improve overall performance.

For the rotor part, when the magnetic flux density of the rotor core permits, the lower area of the slot shape can be expanded, or the cross-section of the end rings of high-speed motors can be increased. This can be especially effective in reducing the temperature rise of enclosed motors. In some cases, the motor's size limits may require improving the insulation class of the winding to resolve temperature rise issues. This may also be necessary and reasonable.

At Germana, we ensure that all our motors undergo strict testing before shipment to avoid such issues for our customers. Choose Germana for your business success!