The insulation of the winding in your electric motor has a major impact on your life expectancy and reliability. Which means that using the wrong insulation class can be very expensive.
The best way to avoid this error is to familiarize yourself with the basic concepts of insulation classes.
The purpose of the motor insulation classes is to describe the insulation capacity of the motor winding to handle heat.
There are currently four classes of electrical motor insulation in use: A, B, F and H (although there are also classes N, R and S). Of these four, B, F and H are the most commonly used.
These classes specify the allowable temperature rise from an ambient temperature of 40 ° C.
Class A:
Maximum temperature rise: 60 ° C
Hot spot over-temperature allowance: 5 ° C
Maximum winding temperature: 105 ° C
Class B:
Maximum temperature rise: 80 ° C
Hot spot over-temperature allowance: 10 ° C
Maximum winding temperature: 130 ° C
Class F:
Maximum temperature rise: 105 ° C
Hot spot over-temperature allowance: 10 ° C
Maximum winding temperature: 155 ° C
Class H:
Maximum temperature rise: 125 ° C
Hot spot over-temperature allowance: 15 ° C
Maximum winding temperature: 180 ° C
The maximum winding temperature is the sum of the ambient temperature (40 ° C) and the permitted temperature rise.
The permitted temperature rise is made up of two parts: the maximum temperature rise for the insulation class plus a hot spot on the temperature allowance.
Why winding temperature is important
When your electric motor operates at a temperature above the allowable winding temperature, the service life will always be reduced.
In fact, an increase of 10 ° C above the maximum allowed can halve the life of the motor insulation.
If you have a Class A insulated motor, the maximum winding temperature will be 105 ° C. If you are operating at 105 ° C, this means 20 ° C above its limits and each increment of 10 ° above this limit reduces the life span in 1/2.
This operating temperature will reduce the engine’s service life to just 1/4 of its original life expectancy!
Remember that the engine’s surface temperature may appear high, but it is still within limits.
Say you have a Class F insulated motor rated for a winding temperature of 155 ° C.
You or one of your technicians inadvertently put your hand on the surface of the engine and notice that the engine is hot.
Is the engine too hot? Maybe, but probably not. A rule of thumb is that the surface temperature is usually only 30 ° C lower than the winding temperature.
So with all that said, an engine that is extremely hot to the touch is not necessarily operating beyond its rated temperature.
Geartech BR currently occupies a prominent position in the country, importing films, polyester compounds, papers and insulating tapes. Currently, our products are used by manufacturers of electric motors, transformers, cables, compressors, fans, etc. Contact us and learn more about our products and services.
