The difference between air compressor inverter and soft starter

The difference between air compressor inverter and soft starter

Soft starter concept

　　Soft start (also known as soft starter, motor soft starter, soft starter)

　　Soft start is a novel motor control device that integrates motor soft start, soft stop, light load energy saving and multiple protection functions.

　　The main composition of soft start is the three-phase parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor. Using different methods to control the conduction angle of the three-phase parallel thyristor, the input voltage of the controlled motor can be changed according to different requirements, and different functions can be realized. Soft starters and frequency converters are two completely different products. Inverter is used where speed regulation is required. Its output not only changes the voltage but also changes the frequency at the same time; the soft starter is actually a voltage regulator, when used for motor starting, the output only changes the voltage without changing the frequency. The frequency converter has all the soft starter functions, but its price is much more expensive than the soft starter, and the structure is much more complicated. The motor soft starter is a soft starter connected in series between the power supply and the controlled motor to control the conduction angle of its internal thyristor, so that the motor input voltage gradually rises from zero in a preset function relationship, until the end of the start, which is given to the motor Full voltage means soft start. In the process of soft start, the starting torque of the motor gradually increases and the speed also gradually increases.

　　What is the difference between soft starter and inverter

　　Soft starter and inverter are two completely different products. Inverter is used where speed regulation is required. Its output not only changes the voltage but also changes the frequency at the same time; the soft starter is actually a voltage regulator, when used for motor starting, the output only changes the voltage without changing the frequency. The frequency converter has all the soft starter functions, but its price is much more expensive than the soft starter, and the structure is much more complicated.

　　 Energy-saving principle of soft starter

　　Motor is an inductive load, the current lags behind the voltage, and most electrical appliances belong to this category. In order to improve the power factor, a capacitive load must be used for compensation, and a capacitor or a synchronous motor must be used for compensation. Reducing the excitation current of the motor can also increase the power factor (HPS2 energy-saving function, reducing the voltage when the load is light, so that the excitation current is reduced, and the COS∮ is increased). Energy-saving operation mode: reducing the voltage at light load reduces the excitation current. The motor current is divided into active and reactive components (exciting components) to increase COS∮.

　　 Energy-saving operation mode: When the motor load is light, the soft starter is in the state of selecting the energy-saving function, the PF switch is hot dialed to the Y position, and the soft starter automatically reduces the motor voltage under the action of current feedback. Reduce the excitation component of the motor current. Thereby improving the power factor of the motor (COS∮). (Most domestic soft starters do not have this function) This function cannot be realized in the contactor bypass state. The TPF switch provides two response times for energy-saving functions: normal and slow. Energy-saving operation mode: automatic energy-saving operation. (Two response speeds: normal and slow) No-load energy saving 40%, load energy saving 5%.

　　 What are the starting methods for soft start?

Use a soft starter connected in series between the power supply and the controlled motor to control the conduction angle of its internal thyristor, so that the motor input voltage gradually rises from zero with a preset function relationship, until the end of the start, the full voltage is given to the motor, which is Soft start, in the process of soft start, the starting torque of the motor gradually increases, and the speed also gradually increases. The soft start generally has the following starting methods.

　　(1) Ramp boost soft start. This kind of starting method is the simplest. It does not have current closed-loop control and only adjusts the conduction angle of the thyristor to increase it as a function of time. The disadvantage is that due to the unlimited current, in the motor starting process, sometimes a large inrush current is generated to damage the thyristor, which has a greater impact on the power grid, and is rarely used in practice.

　　(2) Ramp constant current soft start. This kind of starting method is that the starting current is gradually increased during the initial stage of motor starting, and when the current reaches a preset value, it remains constant (t1 to t2 stage) until the starting is completed. During the starting process, the rate of current rise and change can be adjusted and set according to the motor load. If the current rise rate is large, the starting torque is large and the starting time is short.

　　This starting method is the most widely used starting method, especially suitable for starting fans and pumps.

　　(3) Step start. Turn on, that is, in the shortest time, make the starting current quickly reach the set value, which is a step start. By adjusting the starting current setting value, a quick starting effect can be achieved.

　　(4) Pulse impact start. In the starting stage, let the thyristor turn on with a relatively large current for a short period of time and then fall back, and then linearly increase according to the original set value, and connect to constant current start.

　　This starting method is rarely used in general loads, and is suitable for starting occasions where heavy loads and large static friction need to be overcome.

　　 What is the difference between soft start and traditional decompression starting method? The traditional decompression starting methods of cage motors include Y-q starting, auto-coupling decompression starting, reactor starting and so on. These starting methods are all step-decompression starting, with obvious shortcomings, that is, a secondary surge current occurs during the starting process. The difference between soft start and the traditional decompression start method is: (1) No inrush current. When the soft starter starts the motor, by gradually increasing the conduction angle of the thyristor, the motor starting current linearly rises from zero to the set value. (2) Constant current start. The soft starter can introduce current closed-loop control, so that the motor maintains a constant current during the starting process, and ensures the smooth start of the motor. (3) According to the load conditions and the selection of the power grid relay protection characteristics, it can be freely adjusted to the best starting current

　　 What protection functions does the soft starter have?

　　(1) Overload protection function: The soft starter introduces a current control loop, so it can track and detect the change of motor current at any time. By increasing the setting of overload current and the inverse time control mode, the overload protection function is realized. When the motor is overloaded, the thyristor is turned off and an alarm signal is issued.

　　(2) Phase loss protection function: When working, the soft starter detects the changes of the three-phase line current at any time, and once the current is cut off, it can respond to phase loss protection.

　　(3) Overheating protection function: The temperature of the thyristor radiator is detected through the internal thermal relay of the soft starter. Once the radiator temperature exceeds the allowable value, the thyristor will be automatically turned off and an alarm signal will be issued.

　　( 4) Other functions: through the combination of electronic circuits, other kinds of interlocking protection can also be realized in the system.

　　7. What is a soft start MCC control cabinet?

　　 MCC (Motor Control Center) control cabinet, that is, the motor control center. The soft starter MCC control cabinet is composed of the following parts: (1) the circuit breaker at the input end, (2) the soft starter (including the electronic control circuit and the three-phase thyristor), (3) the bypass contactor of the soft starter, (4) ) Secondary side control circuit (to complete the selection and operation of functions such as manual start, remote start, soft start and direct start), with voltage, current display and fault, running, working status and other indicator lights.

　　Why are some soft starters equipped with bypass contactors?

　　Most soft starters have bypass contactor contacts on both sides of the thyristor. The advantages are:

　　(1) The control cabinet has two starting methods (direct starting, soft starting).

(2) After the soft start is over, the bypass contactor is closed, so that the soft starter will quit operation until it stops, and then put it back in. This prolongs the life of the soft starter, avoids the harmonic pollution of the power grid, and reduces the soft starter. Heat loss of the thyristor in the starter.

　　 Typical application of soft start

　　1. Water pump: Use the pump control function to reduce the water hammer phenomenon of the pump caused by the impact of the liquid flow when starting and stopping, saving system maintenance costs;

　　2. Ball mill: use voltage ramp to start, reduce gear torque wear, reduce maintenance workload, and extend service life;

　　3. Fan: Use a solid soft starter to replace the traditional starter to reduce belt wear and mechanical shock;

　　4. Compressor: The use of current limiting realizes smooth starting and reduces the temperature rise of the motor;

　　5. Crusher: use locked-rotor protection and fast protection to avoid mechanical failure and blockage causing the motor to overheat and burn;

　　6. ​​Conveying machinery: Use soft start and soft stop control to achieve a smooth and gradual start process and smooth reduction