Explosion-proof control box motor positive and negative wiring method

The main electrical components

3 button switches, 2 contactors, 1 thermal overload, preferably 3 fuses for protection of 3 live wires, explosion-proof enclosure, explosion-proof accessories

Positive and negative wiring diagram:

Electrical principle analysis

The motor must achieve positive and negative control, and any two of the phase sequence of its power supply can be adjusted relative to each other (we call commutation). Usually, the V phase is not changed, and the U phase and W are relative regulators, in order to ensure two contacts. When the device moves, the phase sequence of the motor can be reliably exchanged, and the wiring of the upper port of the contactor should be consistent when wiring, and the phase of the lower port of the contactor should be phased. Since the phase sequence of the two phases is reversed, it must be ensured that the two KM coils cannot be energized at the same time. Otherwise, a serious phase-to-phase short-circuit fault may occur, so an interlock must be taken. For safety reasons, the double interlocking reversing control circuit of the button interlock (mechanical) and the contactor interlock (electrical) is often used (as shown in the figure below); the button interlock is used even if the reversing button is pressed at the same time The two contactors used for phase modulation cannot be powered at the same time, and mechanically avoiding phase-to-phase short circuits. In addition, due to the application of the contactor interlock, so long as one of the contactor is energized, its long closed contact will not be closed, so that in the application of mechanical and electrical double interlocking, the motor power supply system is unlikely to phase short circuit, Effectively protects the motor, and at the same time avoids accidents caused by phase short-circuits during phase modulation and burns out the contactor.

Positive and negative operation precautions

Explosion-proof control box In the operation of the forward and reverse operation of the motor, if the forward rotation electromagnetic contactor and the reverse electromagnetic contactor are erroneously operated at the same time, what happens when a closed circuit is formed? The L1 phase of the three-phase power supply The line voltage between the L3 phase and the main contact of the electromagnetic contactor is reversed to form a completely short circuit state. Therefore, a large short-circuit current flows and the circuit is burned. Therefore, in order to prevent a two-phase power short circuit accident, the main contacts of the contactors KM1 and KM2 must not be closed at the same time.

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