Learn common soft start modes and troubleshooting measures

How to start auto soft start?

1. Current limit start

As the name implies, it limits the starting current of the motor. It is mainly used to reduce the starting voltage drop when the load is started at light load. It is difficult to know the starting voltage drop during starting, and the pressure drop space cannot be fully utilized, and the starting torque is lost, which is not good for the motor.

2. Ramp voltage start

The voltage ramps up linearly from small to large. This kind of start-up method is to gradually increase the start-up voltage in the initial stage of motor start-up, and keep it constant when the voltage reaches the preset value until the start-up is completed. This start-up method is the simplest and does not have current closed-loop control. It only adjusts the conduction angle of the thyristor to increase it as a function of time. The disadvantage is that, due to the unrestricted current, in the process of starting the motor, sometimes a large inrush current is generated to damage the thyristor, which has a great impact on the power grid, and is rarely used in practice.

3. Torque control start

The starting torque of the motor is increased linearly from small to large, and its advantages are smooth starting, good flexibility, better protection for the drag system, and extended service life of the drag system. At the same time, it reduces the impact on the power grid when the motor starts, which is an excellent heavy-load starting method, but the disadvantage is that the starting time is longer.

4. Torque plus kick control start

Similar to torque control start, it is also used for heavy load start. The difference is that the static torque of the motor is overcome by the sudden torque at the moment of startup, and then the torque rises smoothly, interfering with other loads, and special attention should be paid when applying it.

5. Voltage Controlled Start

It is an excellent light-load soft-start method when used in light-load start-up situations, where the maximum starting torque of the motor can be exerted under the guarantee of starting voltage drop, and the start-up time can be shortened as much as possible.

Soft start AC protection functions

1. External fault input protection. Instantaneous power-off terminals are used to add special protection devices, such as thermal relays, etc.

2. Loss of pressure protection. After the soft starter is powered off and the power is turned on again, no matter where the control terminal is, it will not start by itself, so as to avoid injury.

3. Start time is too long protection. Due to improper soft starter parameter setting or other reasons, the soft starter will protect itself if it fails to start for a long time.

4. Soft starter overheat protection. When the temperature rises to 80±5℃, the protection will act, and the action time is less than 0.1 seconds; when the temperature drops to 55℃, the overheat protection will be released.

5. Input phase loss protection. Lag time < 3 seconds.

6. Output phase loss protection. Lag time < 3 seconds.

7. Three-phase unbalance protection. The lag time is less than 3 seconds, and the current deviation of each phase is greater than 50% ± 10% as the benchmark.

8. Activate the overcurrent protection. The protection will act when it is continuously greater than 5 times the rated working current of the motor at startup.

9. Run overload protection. The inverse-time thermal protection is based on the rated working current of the motor.

10. Power supply voltage is too low protection. Lag time: When the power supply voltage is lower than 50% of the limit value, the protection will act, and the time will be less than 0.5 seconds. Otherwise, the protection will act when the voltage is lower than the set value, and the time will be less than 3 seconds.

11. Power over voltage protection. When the power supply voltage is higher than the limit value of 130%, the protection action, the time < 0.5 seconds, otherwise the protection action is higher than the set value, the time < 3 seconds.

12. Load short circuit protection. Lag time: <0.1 seconds, the short-circuit current is more than 10 times the nominal motor current rating of the soft start.

Motor soft starter common troubleshooting measures

1. No display after power on

1) Check whether the control power supply is connected.

2) Check whether the display cable is plugged in tightly.

3) Check if there is any problem with the control board.

2. Report missing phase fault

1) When the startup method adopts the electrified method, the operation sequence is wrong. The correct operation sequence should be to send the main power first, and then send the control power.

2) When the power supply phase is missing or the three-phase power is not on, the soft starter protection action (check the power supply).

3) The output terminal of the soft starter is not connected to the load.

4) There is a problem with the control board.

3. The bypass contactor does not pick up after startup

1) During the start-up process, the protection device malfunctions due to the small setting (just re-adjust the protection device).

2) During debugging, the parameter setting of the soft starter is unreasonable (mainly for the soft starter below 55kW, reset the parameters of the soft starter).

3) The control circuit is in poor contact (check the control circuit).

4) There is a problem with the contactor and it cannot be normally pulled in.

5) Control board problem.

4. Air switch tripped

1) The setting value of the long delay time of the air switch is too small or the selection of the air switch does not match the motor (the parameters of the air switch are appropriately enlarged or the air switch is re-selected).

2) The starting voltage parameter of the soft starter is set too high or the starting time is too long (according to the load condition, the starting voltage should be appropriately reduced or the starting time should be shortened appropriately).

3) During the start-up process, due to the large fluctuation of the grid voltage, it is easy to cause the soft starter to issue wrong commands, resulting in an early bypass phenomenon (it is recommended that users do not start high-power motors at the same time).

4) Start with full load at startup (reduce the load as much as possible during startup).

5) There is a problem with the soft start rated current setting.

5. The soft starter reports fault when starting

1) The motor phase is missing (check the motor and peripheral circuits).

2) The main component thyristor in the soft starter is short-circuited.

3) The filter board is broken down and short-circuited.

4) Control board problem.

6. Boot Timeout

1) The parameter settings are unreasonable (re-adjust the parameters, the initial voltage is appropriately increased, and the time is appropriately lengthened).

2) Start with full load at startup (reduce the load as much as possible during startup).

3) Mechanical failure.

4) Control board problem.

7. Unstable current during startup

1) The indication of the ammeter is inaccurate or does not match the transformer.

2) The grid voltage is unstable and the fluctuation is relatively large, causing the soft starter to malfunction.

3) The parameter setting of the soft starter is unreasonable.

8. Soft starter restarts repeatedly

1) During the start-up process, the peripheral protection components act, and the contactor cannot be pulled in, causing the soft starter to start repeatedly (check the peripheral components and lines).

2) There is a problem with the intermediate relay, which cannot be normally pulled in.

3) Control board problem.

9. Short circuit

1) Check the motor wiring and whether the motor is damaged.

2) Overcurrent will break down the soft starter (check whether the power of the soft starter matches the power of the motor, and whether the motor is started with load).

3) The cooling fan of the soft starter is damaged (replace the fan).

4) Frequent starts, high temperature will damage the thyristor (control the number of starts).

5) The filter board is damaged (replace the damaged components).

10. Overcurrent at startup

1) Check whether the mechanical parts of the load or motor are normal.

2) Check whether the motor is short-circuited.

3) Check whether the current parameters and power of the soft start are correct.

11. Three-phase unbalance

1) Check whether the input three-phase power supply is abnormal.

2) Check whether the load side of the motor is abnormal.

3) Soft starter thyristor breakdown short circuit.

4) There is a problem with the control board.