The high-voltage soft starter cabinet is a starting device for high-voltage AC motors. It consists of a three-phase anti-parallel thyristor assembly and its electronic control system connected between the power supply and the controlled motor. The high-voltage solid-state soft starter cabinet is composed of multiple thyristors connected in series and parallel. By controlling the firing angle of the thyristors, the output voltage is regulated to meet the varying voltage and current requirements during the motor starting process. During motor startup, the high-voltage solid-state soft starter gradually increases the motor's terminal voltage according to a pre-set starting curve, enabling smooth acceleration and reducing electrical and mechanical stress on the power grid, motor, and connected equipment. Once the motor reaches its normal operating speed, the bypass vacuum contactor engages, completing the starting process. During motor operation, the high-voltage soft starter continues to monitor the motor, measuring current and voltage in real time, and provides various fault protections.

The working principle of the high-voltage soft starter involves receiving a start command, after which the microprocessor detects the synchronization signal and controls the phase-angle triggering of the thyristors in the main circuit. This gradually increases the motor's current and voltage, ensuring a smooth start. During this process, the RC snubber unit absorbs the peak voltage generated when the thyristors are turned off in reverse. The voltage-balancing resistors ensure that each thyristor in the series circuit experiences an equal voltage. Fiber-optic triggering ensures electrical isolation between the controller and the high-voltage thyristors while also protecting the trigger signals from electromagnetic interference.

Protection functions of the high-voltage soft starter:

Overvoltage and undervoltage protection: Activates and signals when the voltage exceeds or falls below the set range.

Overcurrent protection: Activates and signals when the current during startup or operation exceeds the set value.

Current imbalance: Excessive imbalance in three-phase currents can cause motor vibration and overheating. Protection activates and signals when the imbalance exceeds the set range.

Startup timeout: Activates and signals if the motor starting time exceeds the set limit.

Overload protection: Activates and signals when an overload occurs during motor operation.

Underload protection: Activates and signals in case of underload or loss of load during motor operation.

During motor soft starting, a lower starting current does not necessarily mean better performance. Instead, a smooth start with acceptable current, minimal mechanical stress, and low heat generation indicates good starting performance. After configuration, observe the starting effect and adjust the initial voltage, starting time, and maximum current limit to achieve optimal results. The typical soft start time from initiation to bypass ranges between 15 and 35 seconds. Start times that are too short or too long indicate poor soft starting performance.