Three-phase asynchronous motor and reversing control principle diagram

In figure 1 is the main circuit of three phase asynchronous motor and reversing control and relay control circuit diagram, figure 2 and 3 is a function and its the same external wiring diagram and ladder diagram of PLC control system, among them, the KM1 and KM2 is respectively control the operation of forward and reverse operation of ac contactor. In the ladder diagram, with two guaranteed power way to control the forward and inversion of the motor. Press the start button SB2 forward, X0 to ON, the normally open contacts connected, Y0 and keep, the 'power' by the coil of KM1 coil electricity, motor begins to turn is running. Press the stop button SB1, X2 to ON, the normally closed contact disconnect, make Y0 coil 'electricity', stop running motor. In ladder diagram, the normally closed contact of Y0 and Y1 separately with the other side of the coil in series, can ensure that they are not to ON at the same time, thus KM1 and KM2 of coil electricity at the same time, the safety measures in the relay circuit is called the 'interlock'. In addition, in order to facilitate operations and ensure Y0 and Y1 not to ON at the same time, also set up in the ladder diagram 'button interlocking', is about to start button normally closed contact of the X1 and inversion control forward Y0 coil series, transfer is the starting button X0 normally closed contact with inversion of control Y1 coil in series. Set Y0 to ON, the motor forward, if you want to reverse running at this moment, can not press the stop button SB1, press the start button SB3, reverse the X1 to ON, it's normally closed off contact, make Y0 coil 'electricity', the X1 normally open contacts connected at the same time, make the Y1 'electricity', by the coil in the motor is turning into reverse. Ladder diagram of interlock and button interlocking circuit can only ensure that the output module and Y0 and Y1 corresponding hardware relay normally open contacts snacks will not switch on at the same time. Due to the effect of time delay of the inductance in the process of switching, there may be a contactor has not been broken arc and another has been closed, thus cause instantaneous short circuit fault. Can be used at the time of positive &negative switching delay to solve this problem, but it will increase the workload of programming, can not solve above contactor contact fault caused by the power of short circuit accident. If because of the main circuit current is too large or contactor quality is bad, a contactor's main contact is generated when the power of electric arc welding and the bond, its power coil after contact is still on, but if another diagram of contactor electricity, will cause the three-phase power supply short circuit accident. To prevent this kind of situation, should be set up outside the PLC by KM1 and KM2 auxiliary normally closed contact of the interlock circuit is composed of hardware ( See figure 2) , assuming KM1 is main contact arc welding, at which point it with KM2 coil series auxiliary normally closed contact is in off state, thus KM2 coil may not have electricity. In figure 1 FR is a thermal relay overload protection, asynchronous motor serious overload for a long time, after a certain delay, thermal relay the normally closed contact of disconnection, normally open contact closure. The normally closed contact with the contactor coil series, overload contactor coil power, when the motor stops running and protection. Some thermal relay need to manually reset, namely thermal relay action to it's own reset button, after its contact will recover, namely common open off contact, normally closed contact closure. This thermal relay of normally closed contacts can be like figure 2 in the PLC output circuit, still with the contactor coil in series, this scheme can save photo of an input point. Some thermal relay with automatic reset function, namely, thermal relay action after motor stalling, concatenated in the main circuit components cooling of thermal relay, thermal relay contact automatically recover. If the hot off the normally closed contact of electrical appliances are still in the PLC output circuit, motor stalling over a period of time will by thermal relay contact restorable function again automatically, may cause equipment and personal injuries. Hence the automatic reset function normally closed contact of thermal relay can't connect the PLC controller output circuit, must be in his contact with the input end of the PLC controller ( Can answer the normally open contacts or normally closed contacts) , use ladder diagram to realize the motor overload protection. If use electronic motor overload protector to replace thermal relay, also should pay attention to it is reset.
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