PLC control and timer motor control circuit - positive &negative protection

by:Coolmay     2020-06-03
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three-phase asynchronous motor control line operations as a basic control link, in the electrical control circuit is used very widely. In motor positive and negative conversion, it may be because of the same element normally open, normally closed contact of the switch without time delay, may because the motor capacity bigger or improper operation, make produce serious contact the main contact arc phenomenon, the arc is not completely dies, reversing contactor is closed, can cause the power supply and short circuit, in order to prevent power short circuit, electrical interlocking protection can be used, but in actual use, sometimes HouGuang electrical interlocking protection is not enough, the contactor coil, when the power is its contact may still closed due to welding. If someone hands push another contactor of armature will make both contactor in the off state, so in addition to the electric interlocking should also be equipped with mechanical chain. Mechanical chain more reliably guarantee two contactor won't suck at the same time, but only in the space position closer installed between two contactor. Electrical appliances chain can not restricted by space position, but in the contactor contact welding can't protect you. Don't allow separate adopts mechanical chain in the line, because when a contactor timeliness, press another button of contactor, although due to mechanical interlocking effect, another contactor does not suck, but its coil is through the so-called 'starting current (' Core is not closed, ac contactor coil impedance and large current) , time is too long will be burnt coil.

in order to overcome the above difficulties, here use timer T37, T38 respectively as the protection of the forward and reverse switching device. Since joined the timer operation, can according to the needs of different set of positive &negative switching time, can effectively overcome the positive and negative conversion to may be caused by arc not completely disconnect the power supply when short circuit.

1 relay contact control can improve the electrical schematic diagram

is shown in figure 1, for the electrical principle of main circuit and auxiliary circuit principle diagram. Main circuit is the strong current through the part of the electrical wiring, that is, from the power by the power switch of QS, contactor KM1 or KM2 main contactor, thermal relay FR heating element to the motor M, as shown in figure 1.

auxiliary circuit including the control circuit of the motor, lighting, signal circuit and protection circuit, by relay and contactor coil, relay contactor, contactor, auxiliary contacts, the main electrical appliances ( The command and control, button) , lights, lights, siren and other electrical components. In order to easy to distinguish main circuit and auxiliary circuit, through the strong current of main circuit for the left side of figure 1, through the weak current auxiliary circuit for the right of figure 1. Electrical schematic diagram shows that only electric circuit principle of work, so the electric appliances in figure 1 is generally not said its spatial location, the same electrical each element often painted in a different position according to need. The contactor in as shown in figure 1 KM1, main contactor painting in the main circuit, control circuit of the coil and auxiliary contact drawn in, and for each of the auxiliary contact can be according to the need to draw on different position, but every element of the electrical appliances should be use the same word mark. This expansion illustration for the expression or general electric circuit principle is more convenient. Corresponding I/O configuration diagram 1

in figure 2 is stop button SB1, SB2 is a positive start button, is reverse starting button SB3, FR is thermal relay switch contact. COM to end, KM, KM1, KM2 for contactor, figure 2 the bottom right corner of the graphics for the ac power. 2 is correct inversion of coil. The corresponding I/O allocation table shown in table 1. 2 the corresponding I / 0 distribution list

corresponding I/O distribution as shown in table 1. 3 ladder diagram

this we use Siemens series PLC controller ladder diagram, programming software STEP7 - Micro/WIN32 S7 - 300 programmable controller. As shown in figure 3. 1 off, with positive starting line to form the interlock. The interlock to ensure the won't because of wrong operation and lead to motor and reversing effect at the same time, the motor has played a protective effect. At the same time of press the start button SB2 forward, forward delay timer T37 connected, after the delay for a few seconds, is turn coil connected to the motor is starting. 2 electric closing and locking forward line has been cut off at the same time. In the press the start button SB3 reverse at the same time, the inversion of delay timer T38 connected and delay for a few seconds later reversed coil is energized. By the middle of the delay to make motor are turning to reverse the reversing that may produce arc extinguishing completely, can effectively avoid the reversing the arc directly caused by short circuit accident. 0 losing electricity, thus make positive start button SB2 or reverse starting button SB3 lost electricity. 2 losing electricity, motor will stop.

3 knot language proved by practical application, the improved circuit can not only effectively prevent the circuit when switching power supply and the phenomenon of short circuit, especially for high power motor effect is more obvious. And because this circuit using the timer, can according to the needs of different selectively set the length of the switch time, can get good result in practical application.

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