I. Startup methods of soft starters
1. Ramp-up soft start
This starting method is the simplest, but it lacks closed-loop current control. It only adjusts the thyristor conduction angle to increase it in a certain function of time. Its disadvantage is that, because it doesn't limit current, a large inrush current can sometimes be generated during motor startup, damaging the thyristor and significantly impacting the power grid. Therefore, it is rarely used in practice.
2. Step start
A step start is when the starting current reaches the set value as quickly as possible upon power-on. This rapid start-up can be achieved by adjusting the starting current setting.
3. Ramp constant current soft start
This starting method involves gradually increasing the starting current during the initial stage of motor startup. Once the current reaches a preset value, it remains constant until startup is complete. This is the most widely used starting method, especially suitable for starting loads such as fans and pumps.
4. Pulse impact start
During the initial startup phase, the thyristor is allowed to conduct with a large current for a very short period before dropping back down, and then linearly rising again according to the original set value to connect to constant current starting. This starting method is rarely used in general loads and is suitable for heavy-load starting applications where significant static friction needs to be overcome.
5. Voltage double-slope start
During startup, the motor's output torque increases with voltage, providing an initial starting voltage Us. Us is adjustable according to the load; by adjusting Us to be greater than the static friction torque of the load, the motor reaches its rated speed when the output voltage reaches the speed-up voltage Ur. The soft starter automatically detects the speed-up voltage during startup, ensuring the output voltage reaches the rated voltage when the motor reaches its rated speed.
6. Current-limited start
Current-limiting start is a soft-start method that limits the starting current of a motor to a certain set value during the starting process. The output voltage increases rapidly from zero until the output current reaches the preset current limit Im, and then the output current is maintained. The advantage of this starting method is that the starting current is small and can be adjusted as needed.
II. What parameters should be set for a soft starter?
A soft starter is a device used for controlling the starting of electric motors. It reduces the starting current surge by gradually increasing the motor voltage, thus extending motor life and reducing equipment failures and maintenance costs. The following are the main parameters of a soft starter and their functions:
Acceleration time: The time it takes for the soft starter to gradually increase the voltage of the motor, usually measured in seconds. The acceleration time should be set according to the motor's load and starting current requirements, typically between 1 and 10 seconds.
Initial voltage: The minimum voltage value output by the soft starter when starting, usually expressed as a percentage or voltage value. The initial voltage should be set according to the motor's characteristic curve and load conditions, typically between 30% and 60%.
Maximum current: The maximum current value controlled by the soft starter, usually in amperes. The maximum current setting should be based on the motor's rated current and load conditions, typically 1.5-2 times the rated current.
Power-off time: The soft starter delays the power supply to the motor in the event of a sudden power outage to protect the motor. The power-off time setting should be based on the motor's moment of inertia and load conditions, and is typically between 0.5 and 5 seconds.
Motor rotation: The soft starter should support forward and reverse rotation, and a switch or signal input for forward and reverse rotation of the motor needs to be set.
Overload protection: Soft starters should have overload protection function, and an overload protection value needs to be set, usually in the form of current percentage or current value.
Overheat protection: The soft starter should have overheat protection function, and the overheat protection temperature needs to be set, usually in degrees Celsius.
The parameters of the soft starter need to be set according to the specific motor load and usage requirements to achieve optimal starting performance and protection functions. When setting parameters, relevant safety regulations and operating procedures should be followed to avoid improper operation that could damage the equipment or cause personal injury. If you encounter any uncertainties or difficulties in debugging, you should seek professional assistance promptly.
