Forward and reverse control circuit of button interlock
The operation principle of forward and reverse control circuit of button interlock is basically similar to that of forward and reverse control circuit of electric shock of contactor interlock, and the control circuit is shown in the right figure below.
However, due to the use of composite button, when the reverse button Sb3 is pressed, the normal contact of SB2 in the forward rotation control circuit is first disconnected, the coil of forward rotation contactor KM1 is powered off, the main contact of KM1 is disconnected, and the motor M is powered off; then the normally open contact of reverse button SB2 is closed, so that the coil of reverse contact km2 is powered on, the main contact of km2 is closed, and the motor is reversed. This not only ensures that the positive and negative transfer contacts KMI and km2 will not be connected to the power supply at the same time, but also can directly press the reverse button SB2 to start the reverse without pressing the stop button SB1. In the same way, if you want to change from reverse button to forward operation, just press forward button directly.
The advantages of the forward and reverse circuit are convenient operation and the disadvantages are short circuit fault. If the main contact of the forward transfer contact fails and the fusion welding cannot be disconnected, if the reverse button is pressed for switching, a short circuit fault will occur, so the control circuit of single button interlocking is not safe and reliable.
Forward and reverse control circuit of contactor interlock
Production machinery often requires that the moving parts can run in both positive and negative directions, which requires that the electric motor can run in both positive and negative directions. If any two of the incoming lines of the three-phase power supply of the motor are connected to each other, the reverse direction can be achieved.
Two contactors are used in the control circuit shown in the figure below, i.e. forward switching contactor KM1 and reverse switching contactor km2. When the three pairs of main contacts of the contactor KM1 are connected, the phase sequence of the three-phase power supply is connected to the motor according to ll-l2-l3. When the three pairs of main contacts of contactor km2 are connected, the phase sequence of the three-phase power supply is connected to the motor according to l1-la-li, and the motor rotates in the opposite direction.
The circuit requires that the contactor KMI and the contactor km2 cannot be connected to the power supply at the same time, otherwise their main contacts will be closed at the same time, resulting in a short circuit of two-phase power supply. Therefore, in each branch of KM1 and km2 coils, a pair of dynamic breaking auxiliary contacts of each other are connected in series to ensure that the contactors KM1 and km2 will not be connected to the power supply at the same time. The function of the two dynamic breaking auxiliary contacts KM1 and km2 in the circuit is called Interlocking or interlocking action, these two pairs of moving and breaking contacts are called interlocking contacts.
Forward rotation control: press SB2 → KM1 coil power on → KM1 self-locking contact closed, KM1 interlocking contact open, KM1 main contact closed → motor m running;
Reverse control: first press SB1 → KM1 coil power off → KM1 self-locking contact open, KM1 interlocking contact closed, KM1 main contact open → motor M power off → press Sb3 → km2 coil power on → km2 self-locking contact closed, km2 interlocking contact open, km2 main contact closed → motor M reverse.
The disadvantage of the electric shock forward and reverse control wiring circuit is inconvenient operation, because to change the direction of the motor, you must first press the stop button SB1, and then press the reverse button Sb3 to reverse the motor.