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In the previous column, we explained motor output, efficiency, and losses. In this second installment, we will dive deeper into how "heat generation" and "operating time" affect a motor's performance, and their relationship with the rated output of the motor.

When a motor converts electrical energy into mechanical energy (i.e., rotational motion), losses are inevitably generated in the process, leading to heat generation. This heat affects the internal components of the motor. We will explain this further in this article.

The internal components of a motor, e.g., coils, bearings and resin materials, have heat resistance limits. Exceeding the permissible temperature can shorten the lifespan of these components and lead to failures, in the worst case there is risk of fire or other serious accidents. Therefore, it is essential to operate motors within the appropriate temperature range.

Now, let’s focus on the key points here.

The operating temperature of a motor is determined by the sum of the ambient temperature and the heat generated due to motor losses. This heat is influenced by the operation pattern that is a combination of operating and rest periods, which means that rated output a motor can deliver varies depending on the operation pattern.

Motor Temperature = Ambient Temperature + Motor Heat Generation ≤ Motor Maximum Temperature Limit

Note) Motor Heat Generation is influenced by operation patterns.

The operation patterns used to define this output are known as time ratings, and they are standardized by the International Electrotechnical Commission (IEC). Representative examples include:

S1  Continuous running Duty: The rated output at which the motor can continuously operate.

S2  Short-time Duty: The rated output at which the motor can continuously operate for a specified time, e.g., S2 60min.

S3–S8 Intermittent Duty: The rated output defined for intermittent operation and rest combinations, e.g., S3 5%.

S9 Non-periodic Duty: The rated output for non-periodic variations in load and speed operating conditions.

S10 Duty with discrete constant loads and speeds: Rated output, where each load/speed combination allows the machine to reach thermal equilibrium.

Here are examples of rated outputs for S1, S2, and S3 operation modes. Even with the same motor, you can see that the rated output changes based on the specified operational conditions.

When selecting a motor, what’s most important is to define operation patterns that closely correspond to the actual operation and then determine the motor’s rated output.

Finally, in the next and final column, we will explain motor cooling methods, which significantly affect motor rated output. Cooling is an essential factor in motor installation, enabling compactness, higher outputs, and improved durability.

Please be sure to read our next column as well!