About star-delta step-down start plc ladder diagram circuit diagram

Design a star-delta step-down starting control program for a three-phase asynchronous motor. It is required to turn on the power switch and press the start button SB2. The motor starts with a star connection. After starting to rotate for 5 seconds, k3t3 is powered off and the star start is completed. . In order to effectively prevent arc short circuit, after a delay of 300m3, the E3I2 contactor coil is energized and the motor rotates according to the triangle connection. Overload protection is not considered.

plc wiring diagram

Complete the PLC wiring according to the diagram. The 24V power supply at the input end in the figure can use the DC power supply provided by the PLC, or it can provide a separate power supply according to the power. If the input terminal of the experimental PLC is a relay input, a 220V AC power supply can also be used.

In Figure 1, the main contactor KM of the circuit and the moving and closing auxiliary contacts of the triangular full-voltage operating contactor are connected to the input terminal of the PLC as input signals, which facilitates the actual actions of the two contactors in the program to be monitored and passed through the program. To ensure the safety of the actual operation of the motor. The PLC output terminal retains the hard interlock link of the star and delta contactor coils, and additional soft interlocks must be set up in the program.

Under normal circumstances, after pressing the start button, Yo conducts and the main contact 11 acts. At this time, if there is no fault in 3M1, its moving contact is closed, the moving contact of X2 is closed, and the moving contact of Y0 is closed. Points are connected in series to form self-locking for Y0. At the same time, timer T0 starts counting for 5 seconds.

Yo is turned on, and its moving and closing contacts are closed. In the second line of the program, the two following moving and breaking contacts are in a closed state, thus making Y2 conductive, the contactor KM3_ contact is closed, and the motor starts in star shape. When To counts for 5 seconds, Y2 is disconnected, that is, the star start is completed. The Y1 movable contact in this row acts as an interlock to ensure that the contactor KM3 is in an open state when the triangle is started with full voltage.

At the same time as T0 timing arrives, that is, after the star start is completed, to prevent arc short circuit, it is necessary to delay the turn-on 312. Therefore, the timer I in the third line of the program plays the role of delaying 0.3s.

After T1 is turned on, Y1 is turned on in line 4 of the program, the main contact of k3I2 is activated, and the motor starts in a triangle full voltage state. The Y2 moving breaking contact here also plays a soft interaction role. Since 11 is turned on, T0 loses power, and T1 also loses power due to 10. Therefore, the movable contact of y2 is used to self-lock Y1 in the program.

When the stop button is pressed, Y0 loses power, thus causing 11 or Y2 to lose power. That is, at any time, as long as the stop button is pressed, the motor will stop. (4) Run and debug the program

a. Input the ladder diagram program into the computer.

b. Download the program word to the PLC, and debug and run the program. Observe whether the motor can achieve automatic star-delta reduced voltage start under program control.