You have to understand the typical application of three-phase asynchronous motor in mechanical and electrical equipment!
The basic control circuit of three-phase asynchronous motor is widely used in production and life. For these numerous application circuits, we do not have to make them by ourselves, but we need to know and understand some typical application circuits in order to broaden our horizons and apply them flexibly in production practice.
Suggestions on learning methods
To understand the role of the circuit, we can analyze the functions of the circuit diagram by ourselves. If you don't understand it, you can read the explanations in this article.
Starting Control Circuit of Heavy-duty Equipment
The starting current of heavy-duty equipment is large, but after the start-up (the speed basically reaches the rated value), the current will drop to the rated value. The setting current value of the thermal relay for overload protection is based on the rated current. In order to avoid the protective action of the thermal relay during the starting process, we need to change the direct starting circuit or the decompression starting circuit we learned earlier.
Using Current Transformer and Intermediate Relay to Control Starting of Heavy-duty Equipment
Schematic diagram explanation: press the start button SB2 (3-5), the coils of AC contactor KM, time relay KT and intermediate relay KA get electricity at the same time, the normal contacts of KM (3-5) close, SB2 self-locking (3-5), KT start to delay. Two pairs of normally open contacts KA1 and KA2 are closed in parallel with the two thermal elements of the thermal relay FR. The thermal elements are short-circuited to prevent the high current generated during heavy start-up from causing the FR to operate. At the same time, the three-phase main contact of KM is closed, and the motor gets electricity and starts. With the increase of motor speed, when it reaches the rated speed (i.e. the end of the delay time of KT), the rated current of the motor falls below the rated current, and the normally closed contacts (5-7) which are disconnected when the KT is delayed are disconnected, so that the coil of KA loses power, and the KA usually opens contacts are disconnected, and the thermal relay is put into the circuit to work. The heavy-duty equipment has been started.
Using Current Relay to Start Heavy-duty Equipment
The schematic diagram explains that by pressing the start button SB2 (3-7), the coil of the AC contactor KM2 is electrified and sucked, and the three-phase main contacts of the KM2 are closed. The three main contacts of the AC contactor KM1 and the thermal elements of the thermal relay are short-circuited. The windings of the motor are connected in series with the current relay KI to start the heavy-load process. At this time, the current of the motor is larger and the KI action makes the constant-opening contacts (7-9) of the KI close. In series with KM2's normal open contacts (3-9, closed) to form a self-locking circuit for SB2. The coil of KM2 is still electrified and absorbed. The normal open auxiliary contacts (3-5) of KM2 are closed to make the coil of KM1 electrified. The normal open auxiliary contacts (3-5) of KM1 are closed and self-locked. At the same time, the three-phase main contacts of KM1 are closed to prepare for KM2's short circuit relief. With the increase of motor speed, when the motor reaches the rated speed, the current of the motor also decreases to the rated current. KI operates and releases. The normal open contacts (7-9) of KI are disconnected, which causes the coil of the AC contactor KM2 to be disconnected and released. The three-phase main contacts of KM2 are disconnected, and the short connection of the FR three-phase thermal elements of the thermal relay is relieved. At the same time, the normal open auxiliary contacts (3-5) of KM2 become disconnected. The motor series overload protection thermal breaker FR runs normally and completes the heavy-load starting process.
Typical Conveyor Control Circuit
In the production lines of factories and factories, there are many devices for conveying materials. The reliability and safety of the control lines are very important. By accomplishing this task, we can master the basic methods and skills of designing and making such control devices.
Winch Control Circuit
Explanation of schematic diagram: when hoisting, press the forward start button SB2 (3-5), the AC contactor KM1 coil gets electricity and sucks, and KM1 often opens auxiliary contacts (3-5) to close self-locking, KM1 three-phase main contacts to close, the motor and the electromagnetic lock YB coil are electrified at the same time, the electromagnetic armature is absorbed to the core, the armature is loosened through the transmission mechanism, the brake shoe of the motor is turned on positively. The motor drive device rises.
When the lifting process needs to stop, the stop button SB1 (1-3) can be pressed. The forward current contactor KM1 coil loses power and releases power. The three-phase main contact of KM1 is disconnected and the motor loses power (can still operate by inertia). However, the coil of YB electromagnetically braked is cut off at the same time. Under the action of the spring, the armature is removed from the core, the brake shoe holds the rotor of the motor for braking and the dragging device. Stop it.
When descending, press the reversal button SB3 (3-7), the reversal current contactor KM2 coil is electrically sucked, and the normal open auxiliary contacts (3-7) of KM2 are closed and self-locked, the three-phase main contacts of KM2 are closed, and the coil YB of the motor and electromagnetic lock is electrified, which makes the brake shoe of the brake loosen, the motor electrifies, and the reversal operation dragging device descend.
When the descent process needs to stop, press the stop button SB1 (1-3), the coil of the contactor KM2 loses power, the three-phase main contact of KM2 is disconnected, and the motor loses power. The motor can continue to run for a while depending on inertia. But at this time, the coil of YB with electromagnetic brake is cut off, which causes the brake shoe of the brake to hold the rotor of the motor to brake. The dragging device stops falling.
Multiple conveyor belts for raw material control
Starting process: Press the start button SB2, the AC contactor KM1 coil is electrified and sucked, the auxiliary open contacts (1-2) of KM1 are closed, which acts as self-locking for SB2. The motor M1 is electrified and operated, the first conveyor belt starts to work, and the other pair of auxiliary open contacts (3-4) of KM1 are closed, which is ready for the coil access circuit of AC contactor KM 2. At this time, just press SB4, the second conveyor belt can be put into operation. It can be seen that only when SB2 is pressed, the first conveyor belt is put into operation, and the second conveyor belt is put into operation.