The most commonly used in today's transmission engineering is the three-phase AC induction motor. In many cases, these motors are directly connected to the power system due to their starting characteristics. If you start directly online, it will generate up to 6 times the rated current of the motor. This current overloads the power supply system and the switching devices in series. If it is started directly, it will also produce a higher peak torque, which will not only impact the drive motor, but also damage the mechanical device. For example: auxiliary power transmission unit (V-belt, gear). In order to reduce the direct current, the starting auxiliary device, such as the starting reactor or the autotransformer, should be used, but the conventional method such as starting the reactor or autotransformer can only gradually reduce the voltage, and the soft starter can smoothly raise the terminal. The voltage can be achieved without impact starting. Therefore, the power system and the motor can be optimally protected.
HPMV medium and high voltage soft starters are made up of multiple thyristors connected in series to meet different current and voltage requirements. Controlling the trigger angle of the thyristor can control the output voltage. During the starting process of the motor, the HPMV increases the terminal voltage of the motor according to the preset starting curve to smooth the motor, thereby reducing the electrical and mechanical impact on the grid, the motor itself, and the connected equipment when the motor is started. When the motor reaches normal speed, the bypass contactor is switched on. After the motor is started, the HPMV soft starter continues to monitor the motor and provides various fault protection. In soft stop, the terminal voltage of the motor is smoothly reduced according to the preset stop curve until the motor stops. The soft stop can solve the problems related to pump water hammer and mechanical shock caused by sudden stop.
The operation of HPMV medium and high soft starters can be divided into four processes: start preparation, start process, operation and stop process. The CPU provides comprehensive protection for all processes.
A. Start preparation is completed: During this process, control and power have been applied to the starter, and its protection includes short circuit to SCR, bypass clutch, and contact melting.
Other detection protection features:
Whether the soft starter temperature rise fuse indicator is in the correct phase (if selected)
Power input frequency trip range external input fault
B. Starting process: When the soft starter gets a start command, the following protection functions start to work:
Starting curve acceleration time phase-to-phase balance circuit short circuit / load before detection phase-to-phase leakage start current cumulative overload detection heat capacity detection
C. Operation process: When the motor runs at full voltage and full speed, the motor current will drop below FLA, and the following protection functions will take effect during operation:
Running overload curve lacking phase current too low / out of load over current / electronic positioning pin detection
D. Stop process: Once the soft starter receives the stop command, different protection functions should be selected according to different stop modes. The options are as follows:
Soft stop mode: All protection features will be maintained during operation. At the end of the stop, enter the slide stop protection state below.
Coasting stop mode: The power supply is immediately disconnected from the motor and restored to “start preparation readyâ€. The following protection functions take effect:
Coasting deceleration/rotation deceleration count hourly start number start interval
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