At present, soft starters such as intelligent motor controllers (SMC), Altistart46, MI-CROMASTERVector, PSS, PSD and PS-DH completely replace old starters such as star-delta starters, autotransformers and clutches, and are widely used in water supply systems. Application. Mainly used as the start and stop control of the feed pump. Features:
(1) Both use the microcomputer chip as the core of the starter.
(2) Software intelligence. Summarize the start and stop rules and possible problems of the pump in the water supply system, input the computer in software form, and make the software starter control the operation of the pump, which is more in line with the process requirements of the water system. There are various application configuration schemes, which can be selected by the user and set according to the characteristics of the system.
(3) Powerful network control functions. It can communicate with the water plant control center and the pipe network control center through the network.
(4) It has perfect protection functions such as overheating and overload and is easy to debug.
It is well known to use a soft starter to reduce the starting surge current and power consumption and extend the life of the motor. In the urban water supply system, the pipeline is broken due to surge and water hammer, causing property damage and user water stoppage. Due to the rapid start and stop of the pump system, the motor directly applies the full torque to the pump and liquid.
Since the rate of change of the pump speed is directly related to the rate of change of the output flow rate of the pump, a rapid change in the flow rate of the non-compressible liquid is caused. The acceleration of the pump and liquid from zero speed to full speed is completed in less than 1 s, and the output flow increases from zero to the rated capacity in a short time, so that rapid changes in flow in a short period of time cause surge. All pump systems have an inherent operating point that is the intersection of the pump curve and the system curve. The pump curve is an independent function of its physical properties, and the system curve depends on the length of the pipe, the number of elbow joints, and the way it is installed.
The motor torque characteristics are described by a speed torque curve. The AC induction motor drives a variable torque load, such as a centrifugal pump, where the change in torque is proportional to the change in motor speed. Because the pump is directly connected to the motor output shaft, the change in pressure is proportional to the change in motor torque. Since the system operates at its intrinsic operating point, the motor, pump, and system typically select the motor full load torque equal to the torque required to operate the operating point.