01. Overview of working mode
The working mode of a motor refers to the working mode of the motor under certain conditions. According to the length of the motor's working time, it can be roughly divided into three categories: continuous operation, short-term operation, and intermittent operation.
For ease of understanding, we can imagine the motor as a human being. "Continuous operation" is like a person working 24 hours a day (too miserable). The continuous working system of the motor means that the motor runs continuously without interruption at the rated voltage and rated load. Usually when the user does not specify the working system, the manufacturer should default to continuous working system operation.
Short-term operation is like a person working only one hour a day (envious eyes). The short-term working system of the motor means that the motor runs only within a limited time under rated conditions, with a short working cycle and a long stop cycle. When the motor runs for a specified time under the rated load, it will stop running immediately and can only be restarted after cooling.
If it continues to run beyond the specified time, the motor may overheat and be damaged. There are four standards for the duration of short-term operation of the motor: 10min, 30min, 60min, and 90min.
Intermittent operation is like a person working for 3 hours and resting for 5 hours, and so on. The intermittent working system of the motor means that the motor can only run intermittently under rated conditions, that is, the motor needs to "rest" after working for a period of time. It is usually expressed by the temporary load rate, which is the percentage of the motor's continuous load operation time in a cycle. There are generally four types: 15%, 25%, 40%, and 60%. For example, a motor running at a temporary load rate of 40% works for 4 minutes and "rests" for 6 minutes in a 10-minute cycle, and then alternates in this cycle. If the motor runs beyond the temporary load rate, it may be overloaded and damaged.
However, the actual working cycle of the motor is divided into starting, loading, braking, no-load, rest and other time periods, and in different application scenarios, different combinations are produced according to the duration and sequence of each stage. Therefore, IEC60034-1 (IEC60034 is one of the most important standards among all motor standards, corresponding to the Chinese standard GBT755) divides 10 motor working modes and describes their characteristics, represented by S1~S10. These working modes standardize the use conditions of motors, which can make the comparison and selection of motors from different manufacturers more accurate.
02. Classification Description
The motor duty refers to the specific method of controlling the motor movement. It is a work guide to avoid the motor from overheating and burning out, and it is also a user demand. It also guides you to choose the appropriate motor according to the motor duty. However, in actual applications, many motors have a variety of duty modes, and need to have one or more duty modes at the same time to meet different application scenarios.
S1 duty (continuous duty)
It means that the motor runs continuously at rated load and the temperature reaches a stable value without cooling down or cooling time.
This duty is usually suitable for long-term load situations, such as fans or conveyor belts.
S2 duty (short-time duty)
Run for a given time under constant load, and before reaching thermal stability, stop for a long enough time to allow the motor to cool down (the temperature difference with the cooling medium is within 2K).
In this working system, the motor running time is very short, and the heating time is much shorter than the cooling time. Motors with this working system are commonly found in cranes, household appliance drives, valve controllers, etc.
S3 working system (intermittent cycle working system)
Operate according to a series of identical working cycles that do not reach thermal equilibrium. Each cycle includes a period of constant load operation and a period of shutdown (power-off shutdown time).
Load duty cycle is the ratio of constant load operating time to load cycle.
The starting current of each cycle in this working system has no significant impact on the temperature rise. However, the cycle must last for 10 minutes, and the duty cycle must be one of four types: 15%, 25%, 40%, or 60%. Motors with this working system are commonly found on stamping and drilling machines.
S4 work system (including starting intermittent cycle work system)
Run according to a series of identical working cycles, each cycle includes a starting time that has a significant impact on temperature rise, a constant load running time and a power-off shutdown time.
It is similar to S3, but it adds starting on the basis of S3, so it requires the moment of inertia of the motor load, that is, the acceleration capability of the motor. Motors of this working system are widely used in metal cutting machines, drilling machines, mining hoists, etc.
S5 working system (including intermittent cycle working system of electric braking)
Operate in a series of identical working cycles, each cycle includes a start time, a constant load operation time, a fast electric braking time and a power-off stop time.
Similar to S4, the motor load moment of inertia is required. However, all time periods are too short to reach their respective steady-state temperatures. This working system motor is commonly used in billet rolling mills, manipulator drives, mine hoists, etc.
S6 working system (continuous cycle working system)
Operate in a series of identical working cycles, each cycle includes a period of constant load operation time and a period of no-load operation time, but does not stop.
That is, operating cycle = work (load + no-load), similar to S3, commonly used in presses, cutting machines, etc.
S7 working system (including continuous cycle working system with electric brake)
It runs in a series of identical working cycles, each cycle includes a starting time, a constant load running time and a fast electric braking time, without stopping. That is, S6 with starting is added. It is mainly used in cotton ginning machines.
S8 working system (including continuous cycle working system with variable speed and variable load)
It is more complicated. In this working system, the motor runs by a series of identical working cycles that have not reached the thermal equilibrium state.
Each cycle includes a period of constant load operation at a predetermined speed, and one or more periods of other constant load operation at different speeds. There is no rest time and it runs all the time, but all the time is very short and cannot reach the steady-state temperature.
S9 working system (non-periodic load and speed change working system)
A non-periodic duty system where the load and speed vary within the permitted range. This duty system includes frequent overloads, which can exceed full load. It is relatively complex and is often specified based on actual conditions, such as wind power generation.
S10 duty system (discrete constant load duty system)
It includes no less than 4 discrete load values (or equivalent load) of the duty cycle, which may include no-load operation and shutdown. Under each load, the thermal equilibrium state is reached (even no-load or shutdown), and the minimum load value in a duty cycle can be zero. Compared with S8, it can be considered that there are many constant load movements, which require various loads and times, but do not include acceleration and deceleration.
The duty cycle of the motor has a great influence on the performance and service life of the motor. Correctly selecting the duty cycle of the motor can ensure that the motor can operate safely and have good performance and life under the required load and environmental conditions.
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