Relays and contactors are industrial automation control systems, common electrical components, they are often used in practical applications to control the switch and disconnection operation of the circuit. This paper will elaborate on how to use relays to control contactors, including the basic principles of relays and contactors, the advantages of combined use, circuit connection and use precautions, etc.
1. Basic principle of relays and contactors
1. Principle of the relay
Relay is a kind of electrical switch, which mainly consists of electromagnetic excitation system and linkage system. When the contact of the relay is closed, a path can be formed to allow the current to pass; when the relay contact is disconnected, the path is interrupted and the current cannot pass.
Relay, the working principle is to use the electromagnetic suction principle, when the applied voltage through the coil, the coil will produce a magnetic field, attract the iron core, make the contact closed. When the applied voltage is disconnected, the magnetic field disappears and the contacts return to their original state.
2. Principle of the contactor
Contactor is a kind of electrical element with switching function, which controls the on and breaking of large current by controlling small current. The contactor is mainly composed of the coil, the contact point and the linkage mechanism. When the coil gets the control signal, a magnetic field is generated, and the suction contact is closed and energized; when the coil loses power, the magnetic field disappears and the power failure opens.
Contactors are often used to control high-power circuits, such as motor start and stop, thermoelectric heaters, etc.
2. The combination of relay and contactor use advantages
Usually, the relays and the contactors are used together. The relay controls the on-off state of the contactor through the auxiliary circuit to control the high power circuit and protect the relay. The advantages of the combined use include:
1. Current isolation: the relay and the contactor are isolated by the coils and contacts to protect the control circuit and the high power circuit.
2. Signal amplification: The low-power relay can amplify the signal to a large enough current to control the contactor, which improves the control accuracy and stability of the system.
3. Electrical isolation: the relay and the contactor circuit are separated through gas insulation or groove isolation, which can avoid the interference of arc and noise, and improve the safety of the system.
4. Multi-channel control: through the relay control contactor, multi-channel parallel or series control can be realized to meet different control needs.
3. Circuit connection to the relay and the contactor
There are many ways of connecting circuit between relay and contactor, according to the specific control requirements and the characteristics of electrical equipment.
1. Drive the winding relay
This connection mode is suitable for controlling small and frequent start and stop circuits. The specific connections are made as follows:
(1) To input the current of the control signal into the relay coil;
(2) After the relay coil is connected, the contactor is controlled through the linkage mechanism;
(3) After the contactor is closed, the high-power current path is closed;
(4) After the relay is released, the contactor is opened and disconnects the high-power current path.
2. Parallel relay to drive the contactor
This connection mode is suitable for the control of large scale or multi-channel control circuits. The specific connections are made as follows:
(1) The coils of multiple relays in parallel and excited through the start signal;
(2) After the relay coil is excited, the linkage mechanism controls the contactor at the same time;
3. Series relay to drive the contactor
This connection mode is suitable for the circuit with high stability requirement of the power supply voltage. The specific connections are made as follows:
(1) connect the coils of multiple relays in series and stimulate them in sequence through the start signal;
(2) After the relay is energized successively, the contactor is controlled through the linkage mechanism;
(4) After the relay is released in turn, the contactor is opened and the high power current path is disconnected.
4. Precautions for using the relays and contactors
1. Current and voltage matching: the rated current and voltage of the relay and the contactor should match, and should not exceed its rated value, so as not to damage the components or cause electrical accidents.
2. Coil power: the coil power of the relay is generally less than the coil power of the contactor, and the suitable model should be selected according to the actual demand.
3. Stability and reliability: the selection of relay and contactors should consider the stability and reliability factors, to avoid the adverse effects caused by the working environment or working temperature.
4. Maintenance and maintenance: check and maintain the relays and contactors regularly to keep them clean to prevent the influence of dust and oil pollution on the contacts.
5. Protective measures: When using relays and contactors, attention should be paid to protective measures to avoid damage to electric shock and arc to personal safety and equipment.
In conclusion, relays and contactors are common electrical components in industrial automation control systems, and their combined use can realize accurate control and protection of high power circuits. The stability, safety and reliability of the system can be ensured by correctly connecting the circuit and using the precautions.
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