The application of Newton's law of heat dissipation in the calculation of motor temperature rise

The application of Newton's law of heat dissipation in the calculation of motor temperature rise

Temperature rise is a key and important performance index of the motor. In the actual design and calculation process, the deviation between the design value and the test value often occurs. There are basically two reasons for the analysis. One is the deviation of the manufacturing process from the design. Another reason for the difference between actual data and theoretical data is the irrationality of the design calculation process. Xiaobian today introduces the application of Newton's law of heat dissipation and heat dissipation coefficient in the calculation process of motor temperature rise.

Newton's law of heat dissipation and heat dissipation coefficient

However, there are many factors that determine the ability of the surface to dissipate heat, and it is very complicated to determine the heat dissipation coefficient α very accurately. In general, the alpha value can only be determined experimentally, and the resulting alpha value can only be used for the same or similar conditions, otherwise the reliability or accuracy of the calculation result will be greatly reduced.

The principle of value of correlation coefficient under different characteristics

The heat dissipation coefficient of the hot surface in calm air is related to the characteristics of the surface: the surface of the pig iron or steel coated with putty and lacquer (such as the base of the motor and the bearing shell) α0 is 14.2; the pig iron without the putty but the painted film Or the surface of steel, α0 is 16.7; the surface of copper coated with matt or varnish, α0 is 13.3.

If the speed v is expressed in meters per second, when the motor rotates, k0 = 0.1 on the outer surface of the rotor and k0 = 0.05 to 0.07 at the end of the stator winding of the motor. The coefficient k can be selected according to the following rules:

The most perfect blown surface, k = 1.3;

The surface of the end of the armature, k = 1.0;

The effective length of the armature has a surface, k = 0.8;

Excitation coil surface, k=0.8;

Commutator surface, k = 0.6;

The outer surface of the base (traction motor), k = 0.5.

In real life, many motor manufacturers use the ready-made motor calculation program, but the connotation of the degree itself is not very clear. Ms. Participation suggests that it is necessary to analyze the degree of perfection and reasonableness of the program through necessary means. Without sufficient professional knowledge, the problem is not well solved. Similarly, for the degree of design, the program should be perfected through theoretical derivation and realistic verification.