Why Can't Compressors Start Directly? What Are the Advantages of Soft Starters?
2025-01-01
We know that the direct starting current of a compressor is more than 4 times its rated current.
If the power of the compressor is relatively small, its impact on the power grid is not significant, so we allow it to start directly. Generally, compressors with a power of less than 7.5KW are allowed to start directly.
However, for large compressors, direct starting is not permitted. If its rated current is 100A, the starting current at the moment of startup can reach several hundred amperes. Such a large current has a huge impact on the power grid! It will affect the normal operation of other loads connected to the same power grid. This kind of situation is quite common.
For example, when a large load starts, the light bulbs may dim. We may also encounter this situation at home. For instance, when turning on the TV, the light bulbs may suddenly dim for a moment. Also, due to the excessively large starting current of the load, it is extremely unfavorable to the insulation of the motor windings.
Therefore, large compressors generally need to adopt soft starting.
The so - called soft starting means that in the initial stage of startup, the voltage applied to it is lower than the rated voltage. Common soft - starting methods include starting with a soft starter and starting with an autotransformer for voltage reduction.
When starting with an autotransformer for voltage reduction, in the initial stage of motor startup, a voltage of 60% to 80% of the rated voltage is applied to make it start moving. After it starts rotating, the voltage is switched to the rated voltage for normal operation. This is a simple soft - starting process.
The soft starter is more advanced than starting with an autotransformer for voltage reduction. Although their principles are the same, the voltage provided by the soft starter to the motor gradually increases from 0 to the rated voltage. Its starting process is smoother, the starting effect is better, and the impact on the power grid and the damage to the windings are minimized, which is superior to starting with an autotransformer for voltage reduction.
In modern transmission engineering, the three - phase AC induction motor is the most commonly used. In many cases, due to its starting characteristics, these motors are directly connected to the power supply system.
To reduce the starting current, starting auxiliary devices such as starting reactors or autotransformers should be used. However, conventional methods such as starting with a reactor or an autotransformer can only reduce the voltage gradually, while the soft starter can achieve a shock - free start by smoothly increasing the terminal voltage.
Advantages of soft starting:
If the power of the compressor is relatively small, its impact on the power grid is not significant, so we allow it to start directly. Generally, compressors with a power of less than 7.5KW are allowed to start directly.
However, for large compressors, direct starting is not permitted. If its rated current is 100A, the starting current at the moment of startup can reach several hundred amperes. Such a large current has a huge impact on the power grid! It will affect the normal operation of other loads connected to the same power grid. This kind of situation is quite common.
For example, when a large load starts, the light bulbs may dim. We may also encounter this situation at home. For instance, when turning on the TV, the light bulbs may suddenly dim for a moment. Also, due to the excessively large starting current of the load, it is extremely unfavorable to the insulation of the motor windings.
Therefore, large compressors generally need to adopt soft starting.
The so - called soft starting means that in the initial stage of startup, the voltage applied to it is lower than the rated voltage. Common soft - starting methods include starting with a soft starter and starting with an autotransformer for voltage reduction.
When starting with an autotransformer for voltage reduction, in the initial stage of motor startup, a voltage of 60% to 80% of the rated voltage is applied to make it start moving. After it starts rotating, the voltage is switched to the rated voltage for normal operation. This is a simple soft - starting process.
The soft starter is more advanced than starting with an autotransformer for voltage reduction. Although their principles are the same, the voltage provided by the soft starter to the motor gradually increases from 0 to the rated voltage. Its starting process is smoother, the starting effect is better, and the impact on the power grid and the damage to the windings are minimized, which is superior to starting with an autotransformer for voltage reduction.
In modern transmission engineering, the three - phase AC induction motor is the most commonly used. In many cases, due to its starting characteristics, these motors are directly connected to the power supply system.
To reduce the starting current, starting auxiliary devices such as starting reactors or autotransformers should be used. However, conventional methods such as starting with a reactor or an autotransformer can only reduce the voltage gradually, while the soft starter can achieve a shock - free start by smoothly increasing the terminal voltage.
Advantages of soft starting:
- Reduces the starting current of the motor, decreases the power distribution capacity, and avoids the investment in capacity expansion.
- Minimizes the starting stress and extends the service life of the motor and related equipment.
- The smooth starting and soft stopping avoid the surging problem and water - hammer effect of traditional starting equipment.
- It has multiple starting modes and a wide range of settings for current, voltage, etc., which can adapt to various load conditions.
- Can effectively reduce the starting current and power distribution capacity, avoiding the investment in capacity expansion.
- It can start/stop the motor smoothly without step - by - step changes, avoiding the mechanical and electrical impacts caused by traditional starting methods such as direct starting, star - delta starting, and autotransformer step - down starting.
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