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About the selection of electronic soft starter·Part 3

Sep 08, 2020

About the selection of electronic soft starter·Part 3

What issues should be considered when applying electronic soft starters? As a soft starter, we must first look at its starting performance and stopping performance. The current soft starter has the following five starting methods:

1. What is a soft starter? A soft starter is a new device used to control a squirrel cage asynchronous motor. It is a novel motor control device that integrates motor soft start, soft stop, light load energy saving and multiple protection functions. Called SoftStarter. Its main composition is a three-phase parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor. Use different methods to control the conduction angle of the three-phase parallel thyristor, so that the input voltage of the controlled motor changes according to different requirements, and different functions can be realized.

2. The scope of application of the soft starter. In principle, cage asynchronous motors can be applied to various applications that do not require speed regulation. The soft starter is especially suitable for various pump loads or fan loads, where soft start and soft stop are required.

3. What is the difference between soft start and traditional decompression start mode. The traditional decompression start methods of cage motors include Y-△ start, auto-coupling decompression start, reactor start, etc. These starting methods are all step-decompression starting, with obvious shortcomings, that is, a secondary surge current occurs during the starting process. Due to the backward technology of the traditional decompression starting method, the country has clearly ordered it to be eliminated. The difference between soft start and traditional decompression start 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. There is no impact on the motor, which improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

(2) There is a soft stop function, that is, smooth deceleration and gradual shutdown. 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, which can be selected according to the load conditions and the characteristics of the grid relay protection, and can be freely steplessly adjusted to the best starting current.

4. What is the difference between it and the inverter? Soft starter and inverter are two completely different products. The frequency converter is used where speed regulation is required, and 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 starting the motor, 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.

5. 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 harmonics generated by the soft starter can be avoided when the motor is running

(2) The soft-start thyristor only works when starting and stopping, which can prevent the thyristor from heating during long-term operation and prolong its service life.

(3) Once the soft starter fails, the bypass contactor can be used as an emergency backup.

6. The main features of SAFESAVE soft starter:

(1) SJR3-2000 series is the latest soft starter developed by our factory. Based on the SJR2 series products, it has expanded new functions such as text display, industrial communication and various protections. This product will eventually be an upgrade and replacement of the SJR2 series. It shares the same technical framework with SJR3-3000.

Applicable standard: IEC 60947-2-2: 2002

(2) According to market demand, our company has made further technical improvements to the software and structure of the soft starter SJR3-2000 series. The soft starter provides a complete motor protection function, including start control. Operation and overload, lack of phase, three-phase unbalance, overvoltage, undervoltage protection, etc. As another major achievement of the intelligent application of motor protection and network technology, it simplifies the circuit, reduces the volume, reduces the cost, and makes installation and use more convenient.

(3) Multi-control support

Programmable relay output

Programmable fault relay output

4~20mA DC analog output

RS485 communication input/output.

(4) It is the first domestic case to realize the real one-to-three control, no external frequency conversion soft-start controller, no external complicated logic circuit, and it is really convenient to use three-for-one or one-for-one as required in real life to ensure reliability of. In some manufacturers, the bypass delay is realized by an external circuit. The computer board has less functions, more and more electrical components, and many faults.

7. The company's soft starter has three adjustable points:

(1) Starting voltage (torque): Different loads require different starting voltages. When starting the load, the initial voltage is higher, but the specific voltage cannot be determined, but the soft starter of our company is at this point Can be adjusted.

(2) Starting time: different loads require time adjustment. Adjustment method: If the starting time is generally 12 seconds, the measurement is completed in 6 seconds (the current reaches the highest value, and the sudden decrease is completed), and it can be adjusted to 6 seconds.

(3) Soft stop time adjustment (mainly used on water pumps to eliminate water hammer effect): Make the system more stable. As the name implies, current limiting starting is to limit the starting current of the motor. It is mainly used to reduce the starting voltage drop when starting at light load. It is difficult to know the starting voltage drop during starting, and the voltage drop space cannot be fully utilized, which will result in loss of starting torque, which is not good for the motor. Ramp voltage starting, as the name implies, is a linear rise in voltage from small to large. It changes the traditional step-down starting from stepless to stepless. It is mainly used for heavy-load starting. Its disadvantage is that the initial torque is small and the torque characteristics The parabolic rise is not good for the drive system, and the long starting time is harmful to the motor. Torque control starting is used for heavy-load starting. It increases the starting torque of the motor linearly from small to large. Its advantages are smooth starting, good flexibility, better protection for the drive system, and its purpose is to protect The drag system extends the service life of the drag system. At the same time, it reduces the impact of the motor on the power grid when starting, which is the best way to start heavy load.