220v motor, the capacitor will "single-phase" alternating current split into "two-phase" alternating current phase close to 90 degrees, so that the motor to produce a rotating magnetic field. Therefore, the two-phase winding in any phase of the winding head and tail alignment, you can change the direction of rotation of the magnetic field, the motor steering then changed.
Electric change the direction of rotation principle:
1, the use of two contactors KM1, KM2 switching motor three-phase power supply phase sequence, but the two contactors can not be absorbed, if at the same time, will cause a short-circuit power supply accidents, in order to prevent such accidents.
2, in the circuit should take a reliable interlock, the use of buttons and contactors double interlock motor positive and negative two-direction operation of the control circuit.
220v motor to change the direction of rotation, the specific line is analyzed as follows:
3, positive start: 1, close the air switch QF connected to the three-phase power supply 2, press the positive start button SB3, KM1 energized suction and self-locking, the main contact closure connected to the motor, the motor at this time, the phase sequence is L1, L2, L3, that is, the positive direction of operation.
4, reverse start: 1, close the air switch QF connected to the three-phase power supply 2, press the reverse start button SB2, KM2 energized suction and self-locking through the auxiliary contacts, normally open main contact closure switching the three-phase power supply of the motor phase sequence, the phase sequence of the motor is L3, L2, L1, that is, the reverse operation.
5, interlock link: with a prohibit function in the line to play a safety protection role 1, contactor interlock: KM1 coil circuit into the KM2 normally closed auxiliary contacts, KM2 coil circuit into the KM1 normally closed contacts. When the positive contactor KM1 coil energized action, KM1 auxiliary normally closed contacts disconnect the KM2 coil circuit, if the KM1 power suction, you must first make the KM2 power-off release.
Expanded:
Methods of changing the direction of rotation of various motors:
1. Split-phase motors*** have two sets of wire gardens, one of which is the running wire garden, and the other - the starting wire garden which has a higher resistance. Reversing the two wire ends of any of these two sets of coils will allow the motor to rotate in the opposite direction.
2, push reject type motor has a set of armature wire garden, a only commutator and a set of brush grip, this motor and DC motor is roughly the same, just brush by the heart switch short circuit. Usually, move the relative position of the brush on the commutator, can change the direction of rotation of the motor.
3, shaded-pole type motor Because only a group of wires connected to the AC power supply on the run, so can not be used to reverse the wire end to change the direction of rotation of the motor. Usually, the stator core is taken out and reversed to reverse the direction of the motor.
4, ordinary series excitation motor change the armature or magnetic field of the power supply wire head can change the direction of rotation of the motor.
Motor to change the direction of rotation principle:
5, its auxiliary normally closed contacts reset, which prevents the KM1, KM2 at the same time, resulting in a short-circuit between the phases of the line link is called interlocking link. 2, button interlock: in the circuit used to control the button operation of the positive and negative transmission control circuit, button SB2, SB3 have a pair of normally open contacts, a pair of normally closed contacts.
6, these two contacts are connected to the KM1, KM2 coil circuit. For example, the normally open contact of button SB2 is connected in series with the coil of contactor KM2, and the normally closed contact is connected in series with the coil circuit of contactor KM1. The normally open contact of pushbutton SB3 is connected in series with the contactor KM1 coil, while the normally closed contact is connected in series with the KM2 coil circuit.
7, so that when pressed SB2 only contactor KM2 coil can be energized and KM1 disconnected, press SB3 only contactor KM1 coil can be energized and KM2 disconnected, if at the same time press SB2 and SB3, the two contactor coils can not be energized. This plays the role of interlocking.
8, motor forward (or reverse) start operation, do not have to press the stop button to make the motor stop, you can directly press the reverse (or forward) start button, so that the motor into the opposite direction of operation. The overload protection of the motor is accomplished by the thermal relay FR.
Baidu Encyclopedia-Motor Forward and Reverse