To prevent the motor from starting the reversal (forward rotation) when it is in a forward (reversed) state. A short circuit occurs that causes the main circuit to occur. Hardware interlocking occurs when connecting control circuits. The interlocking circuit is divided into three types, one is the button interlock, the second is the contactor interlock, and the third is the button contactor composite interlock. The three circuits are analyzed separately.
1. Button interlock circuit
The pushbutton switch commonly used in motor forward and reverse control circuits has two pairs of contacts. One pair of normally closed contacts and one pair of normally open contacts. Pushbutton interlocking is the series of normally closed contacts of the forward start button into the reverse start control circuit. Connect the normally closed contacts of the reversed start button in series with the forward start control circuitry. The advantage of this control method is that it effectively avoids the short circuit caused by the simultaneous pressing of the forward and reverse start buttons. The disadvantage is that when switching forward and reverse states, the stop button must be pressed before another start button can be pressed. Despite this operation, if the main contact of one contactor is adhesion, a short circuit can also occur when switching to another state. The control schematic is as follows:
2. Contactor interlock circuit
Contactor interlocking is the effective use of the contactor's normally closed auxiliary contact to prevent short circuit accidents due to adhesion of the main contact of the contactor. Suppose the main contact of a contactor is adhesion due to an arc burn. The auxiliary normally closed contact of this contactor does not reset after the stop button is pressed. Therefore, the contactor in another state will not accress. When selecting a start button switch, only a pair of pushbutton switches with normally open contacts are required to be used. This control circuit also had certain applications in the early days. The control schematic is as follows:
3. Composite interlock control circuit
Due to the continuous enrichment of experience in production labor, a safe and reliable control circuit came into being. That's the button and contactor composite interlock circuit. It combines the advantages of the first two control circuits. The safety of the operator and equipment is fully effective. The following two figures show the direction of the control loop current during the forward and reverse simulation operation. and the direction in which the contactors and motors are running.
Composite interlock forward control circuit
4. The motor is turning forward to start the control process
When pressing the forward start button SB2, the current through the fuse FU2 thermal relay normally closed contact 95, 96 stop button SB1 normally closed contact 11, 12 forward start button SB2 normally open contact 13, 14 reverse start button SB3 normally closed contact 11, 12 reverse contactor KM2 normally closed auxiliary contact 11, 12 forward contactor KM1 coil A1, A2 zero line to form a loop. https://www.diangon.com/m408551.html positive contactor KM1 suction. The motor is spinning. At the same time, the normally open auxiliary contact of the forward contactor KM1 is also suctioned to form a self-locking. KM1's normally closed auxiliary contacts 11, 12 are disconnected to form an interlock. After releasing the forward start button, the current of the control loop is formed through the normally open auxiliary contacts 13 and 14 of KM1. The motor continues to run forward.
Composite interlock inversion control circuit
5. Motor forward rotation switching reverse control process
When the motor presses the reverse start button SB3 when the motor is running forward, the normally closed contacts 11 and 12 of the reverse start button SB3 are first disconnected, cutting off the power supply circuit of the km1 coil of the forward contactor. De-energizes the forward contactor KM1 coil. Thus km1 main contact and normally closed auxiliary contact 11, 12 reset. The current is formed by the fuse FU2 thermal relay normally closed contact 95, 96 stop button SB1 normally closed contact 11, 12 reverse start button SB3 normally open contact 13, 14 forward start button SB2 normally closed contact 11, 12 forward contact km1 normally closed auxiliary contact 11, 12 reverse contactor KM2 coil A1, A2 zero line. Reverse contactor KM2 suction. The motor is reversed. At the same time, the normally open auxiliary contact of the reverse contactor KM2 is also suctioned to form a self-locking. After releasing the reverse start button, the current of the control loop is formed through the normally open auxiliary contacts 13 and 14 of KM2. The motor continues to run in reverse.
Control lines are prone to failure
In the motor forward and reverse control circuit, the fault parts that are prone to occur are the forward and reverse start button rotation, the main contact of the forward and reverse contactor, the thermal relay, the motor bearing, etc. Why are the above parts prone to failure? Since the start button is a component that needs to be operated frequently, it is easy to damage the button switch if the force is not mastered well during the operation. The main contact of the contactor is easily burned by the arc when it is absorbed and disconnected. The large starting current is also easy to fatigue the bimetallic plate of the thermal relay and cause malfunction. The motor produces a large torque when switching in forward and reverse and damages the bearing.