About the principle of medium voltage soft starter

About the principle of medium voltage soft starter


Generally, medium voltage soft starters of manufacturers are equipped with a variety of motor acceleration methods as standard, so different applications can be programmed to select a more suitable starting method. When the motor reaches full speed and the current drops to the operating level, the bypass contacts The device will pull in. The bypass contactor is used to shunt the current on the thyristor to prevent the current from passing through the thyristor for a long time to form heat accumulation on the SCR. At this time, the soft starter can make the motor run at full voltage and protect the motor in real time.


The medium-voltage soft starter actuator is a thyristor valve group, and the valve group is composed of thyristor anti-parallel modules in series. Trigger fiber sync trigger.
The thyristor trigger uses the final drive board to transmit the trigger signal, and the trigger power adopts a high-reliability low-voltage power supply (note: high-standard electrical isolation technology is used) to obtain energy from the low-voltage side; the main circuit voltage and current are isolated by high-voltage transformers. And the signal is collected after being isolated by the secondary micro-transformer.


The principle of the medium-voltage soft starter is the same as that of the low-voltage soft starter, except that the triggering requirements of the thyristor are higher. For reliable triggering, a synchronization signal must be used to force the thyristor to be turned on.

Usually pay attention to check the environmental conditions of the soft starter to prevent operation under the environmental conditions that exceed its allowable conditions. Pay attention to check whether there are objects around the soft starter that hinder its ventilation and heat dissipation, and ensure that there is enough space (greater than 150mm) around the soft starter.

Regularly check whether the terminals of the distribution line are loose, and whether the components in the cabinet are overheated, discolored, burnt odor and other abnormal phenomena.
Clean the dust regularly so as not to affect the heat dissipation, prevent the thyristor from being damaged due to excessive temperature rise, and also avoid leakage and short circuit accidents caused by dust accumulation.
The dust can be cleaned with a dry brush, and can also be used for leather tiger blowing and vacuum cleaner suction. For large dirt, use an insulating rod to remove. If possible, it can be blown off with compressed air of about 0.6MPa.
Usually pay attention to observe the operation of the fan. Once the fan speed is slow or abnormal, it should be repaired in time (such as removing grease, dust, adding lubricating oil, and replacing damaged or deteriorated capacitors). The damaged fan should be replaced in time. If the soft starter is used without a fan, the thyristor will be damaged.
If the soft starter is used in a humid environment or is prone to condensation, it should be dried with an infrared light bulb or a hair dryer frequently to remove moisture to avoid leakage or short circuit accidents.