Electronic soft starter selection - Solutions - Huaqiang Electronic Network

Photocoupler

What issues should I consider when applying an electronic soft starter? As a soft starter, we must first look at its starting performance and parking performance. The current soft starter has the following five starting methods:
Soft Starter Troubleshooting 1. What is a soft starter?
The soft starter is a new type of motor control device used to control the squirrel-cage asynchronous motor. It combines the soft start of the motor, soft stop, light load energy saving and various protection functions. It is called Soft Starter in foreign countries. Its main component is a three-phase parallel thyristor connected in series between the power source and the controlled motor and its electronic control circuit. Different methods are used to control the conduction angle of the three opposite parallel thyristors, so that the input voltage of the controlled motor can be changed according to different requirements, and different functions can be realized.
2. What is the application range of the soft starter?
In principle, cage asynchronous motors are suitable for all applications where speed regulation is not required. The soft starter is especially suitable for various pump type loads or fan type loads, where soft start and soft stop are required.
3. What is the difference between soft start and traditional decompression start?
Conventional decompression starting methods for cage motors include Y-â–³ starting, auto-decompression starting, and reactor starting. These starting methods are all graded decompression starting, and there are obvious disadvantages, that is, secondary inrush current occurs during starting. Due to the backward technology of the traditional decompression starting method, the state has already eliminated it.
The difference between soft start and traditional decompression start mode is:
(1) No inrush current. When the soft starter starts the motor, the motor starting current is linearly increased from zero to the set value by gradually increasing the conduction angle of the thyristor. No impact on the motor, improve the reliability of power supply, start smoothly, reduce the impact torque on the load machine, and extend the service life of the machine.
(2) There is a soft parking function, that is, smooth deceleration, and gradually stop, it can overcome the shortcomings of instantaneous power failure, reduce the impact on heavy-duty machinery, avoid the water hammer effect of the elevation water supply system, and reduce equipment damage.
(3) The starting parameters are adjustable. According to the load condition and the grid relay protection characteristics, it can be freely and steplessly adjusted to the optimal starting current.
4. What is the difference between it and the inverter?
Soft starters and frequency converters are two completely different applications. The inverter is used for speed regulation. The output not only changes the voltage but also changes the frequency. The soft starter is actually a voltage regulator. When the motor starts, the output only changes the voltage and does not change the frequency. The frequency converter has all the soft starter functions, but it is much more expensive than the soft starter and the structure is much more complicated.
5. Why are some soft starters equipped with bypass contactors?
Most soft starters have bypass contactor contacts on either side of the thyristor, which have the following advantages:
(1) The harmonics generated by the soft starter can be avoided when the motor is running. (2) The soft-start thyristor only works when starting to stop, which can avoid long-term operation and heat the thyristor and prolong the service life.
(3) Once the soft starter fails, the bypass contactor can be used as an emergency backup.
6. The main features of Zhitong soft starter:
(1), the company adopts full digital control: the single-chip CPU of the soft starter directly triggers the thyristor through the trigger optocoupler, without environmental interference, drift, temperature and humidity without interference. The reliability, the operability and the safety are greatly improved, and the circuit is simple and the volume is small.
(2), the company's single-chip CPU is mainly imported.
(3) The first domestic real-time one-to-three control, no external frequency conversion soft start controller, no external complicated logic circuit, and really need to be used in real life to ensure the use of three standby ones or one standby one to ensure reliable. Some manufacturers, bypass delay, external circuit implementation, computer board features, electrical components, complex, more faults, one by three external circuit implementation.
7, the company's soft starter has three points to adjust:
(1), starting voltage (torque):
The starting voltage is different for different loads. When the load is required to start, the initial voltage is higher, but the specific voltage is not certain, but our soft starter can be adjusted at this point.
(2), starting time:
The load is different and requires time adjustment. Adjustment method: If the starting time is generally 12 seconds, the measurement is completed in 6 seconds (current reaches the highest, suddenly decreases, then completed), adjustable to 6 seconds.
(3), soft stop time adjustment (mainly used on the water pump to eliminate the water hammer effect): make the system more stable.


As the name suggests, the current limiting start is to limit the starting current of the motor. It is mainly used to reduce the starting pressure drop when the load is lightly loaded. It is difficult to know the starting pressure drop at the start, and the pressure drop space cannot be fully utilized, and the starting torque is lost, which is unfavorable to the motor. As the name suggests, the ramp voltage start-up is a linear rise of the voltage from small to large ramp. It changes the traditional step-down start from stepped to stepless, mainly used for heavy-duty starting. Its disadvantage is that the initial torque is small and the torque characteristics are The parabolic rise is not good for the drag system, and the long start-up time is detrimental to the motor. Torque control start is used in heavy-duty starting. It is to increase the starting torque of the motor from small to large. It has the advantages of smooth starting, good flexibility and better protection for the drag system. Its purpose is to protect Drag the system to extend the life of the drag system.
At the same time, it reduces the impact on the grid when the motor starts, which is the optimal heavy-duty starting method. Its disadvantage is that the starting time is longer. The torque plus kick control start is similar to the torque control start. It is also used for heavy load starting. The difference is that the sudden torque is used to overcome the static torque of the motor at the moment of starting, and then the torque rises smoothly and the starting time is shortened. However, the kick will send a sharp pulse to the grid, interfering with other loads, and pay special attention to the application. The voltage control start is used in the case of light load starting. The maximum starting torque of the motor is achieved under the guaranteed starting pressure drop, and the starting time is shortened as much as possible. It is the optimal light load soft starting mode.
In summary, it is not difficult to see that the most suitable and most advanced starting method should be voltage control starting and torque control starting and torque plus kick control starting. The current soft starters are mostly current-limited start-up and ramp-wave voltage start-up. It is the most primitive and lowest-level way (such as "ABB" soft start and most domestic manufacturers), and there are current limit start and torque increase. Jump control starts. Only the "Reynolds" soft starter achieves voltage control and pure torque control and torque plus kick control start. "AB", "Schneider", "Siemens" are the start-up start and torque plus jump control start.
There are three parking modes: one is free parking, the other is soft parking, and the third is brake parking. The biggest parking benefits of electronic soft starters are soft parking and brake parking. Soft parking eliminates the anti-inertial impact of the drag system due to free parking. Brake parking replaces reverse brake parking in certain situations.
Reliability choice: Reliability is divided into three aspects, one is the short-circuit self-protection of the product, the second is the fault-free shutdown protection, and the third is the product failure rate. The first two items can be identified by the product manual. In addition to the self-protected short-circuit protection of “Reynold”, domestic products generally do not have short-circuit protection. A fast fuse is required, and the automatic switch cannot protect the electronic soft starter. Foreign "ABB" does not have its own short-circuit protection, and a quick-blow fuse is required. Trouble-free shutdown protection See if its soft start has a green unit (KGL), and all the power electronics world problems are trouble-free shutdown (interference shutdown). At present, only the popular "Reynold" electronic unit is installed in the electronic soft-selling market.
The choice of intelligent control function: pay attention to its intelligence level when selecting soft, whether it has a computer interface, whether the interface has a communication address and program, whether it can reach the communication control and the fault diagnosis function. At present, it is found that these functions are complete only with the soft start of "Renole", and have been well applied in the control of urban drainage computer in Tianjin.
Other aspects should also consider whether the protection function is complete and the cooling mode and operation mode, such as: over current protection, over voltage protection, single ground protection, upper and lower phase failure protection, three-phase unbalance protection, phase reversal protection, etc. The cooling method is divided into mechanical air cooling and natural air cooling. Whether the cabinet needs to be mechanically ventilated, the components are arranged, etc., the mechanical air-cooled cabinet is mechanically ventilated, the soft-up can not be discharged on the upper part, and the mechanical air-cooling should also consider the inclination. Natural air cooling does not require this. The operation mode is divided into online type and non-online type. When selecting the type, try to use non-online type.