Working principle of power relay

The relay consists of four parts: coil, magnetic circuit, reaction spring and contact. After the coil is energized, electromagnetic attraction is generated, which drives the armature of the magnetic circuit to attract and close the contact, resulting in displacement action. The magnetic circuit is composed of an iron core, an iron yoke and an armature, and its task is to establish a magnetic path for the magnetic flux generated by the coil.

 

The function of the reaction spring is to provide the armature with a repulsive force in the opposite direction of action, and to help the armature and contacts reset when the coil is powered off. Contacts are used for external control outputs, including normally closed contacts and normally open contacts.

 

After the coil is powered on, the relay is closed, the normally closed contact is opened, and the normally open contact is closed. After the coil is powered off and released, the normally closed contact and the normally open contact are reset to the initial state.

 

Contact principle of power relays

Electromagnetic attraction: When a certain voltage or current is added to both ends of the coil of the power relay, the coil generates magnetic flux through a magnetic circuit composed of iron core, yoke iron, armature and air gap. Under the action of magnetic field, the armature is drawn to the pole surface of the core, which pushes the normally closed contact to break and the normally open contact to close.

 

Contact closing principle: When the dynamic and static contacts of the relay contact, contact rebound will occur, that is, uncontrolled gap opening and closing. The joule heat generated by the electric arc and current at this time greatly affects the opening and closing ability of the relay.

 

Contact breaking principle: When the contact is broken and the load is cut off, dazzling sparks and arcing will occur, and the arc will continue until the arc voltage falls below the minimum arc voltage value, which will cause great damage to the contact. Different contact materials and contact gap sizes directly affect the radiation state of arc electrons and the ease of arc occurrence, so they are important conditions to determine the arc state.

 

Measurement methods for power relays

Contact resistance: Use the resistance of the multimeter to measure the resistance of the normally closed contact and the moving point, and the resistance value should be 0 (more accurate measurement can get the contact resistance value within 100 milliohm); The resistance value of normally open contact and moving point should be infinite. This can help distinguish between normally closed and normally open contacts.

 

Measuring coil resistance: Use the multimeter R×10Ω to measure the resistance value of the power relay coil to determine whether the coil is open.

 

Measure the pulp-in voltage and pulp-in current: Use an adjustable regulated power supply and ammeter to input a set of voltages to the power relay, and string an ammeter into the supply loop for monitoring. Gradually increase the supply voltage, when you hear the power relay suction sound, record the suction voltage and current. To get more accurate results, try and average several times.

 

Measure the release voltage and release current: After the power relay draws, gradually reduce the supply voltage, and record the voltage and current when you hear the release sound of the power relay again. Similarly, multiple attempts can be made to achieve an average release voltage and release current.

 

common problems and treatment measures

Power relays in practical applications may encounter some common problems and their corresponding treatment measures, the following are some of the main problems and solutions:

 

Contact loosening and cracking:

This is caused by poor riveting of the contact or high material hardness and excessive pressure. Treatment measures include re-riveting the contact point, selecting the appropriate hardness of the material, and annealing. During manufacturing, riveting or welding, the boundary between intermediate sampling for the first inspection and self-inspection for the final inspection should be followed to improve assembly quality.

 

The relay does not work:

This may be due to a power failure, improper relay sensitivity setting, or a damaged relay component. Solutions include checking the power connection, adjusting the sensitivity of the relay, or replacing the relay element.

 

Relay heating is too high:

This may be due to relay overloading, poor ventilation, or relay damage. Treatment measures include checking whether the load current is within the specification range, adding heat dissipation measures or replacing relays.

 

Contact adhesion:

When the contact of the relay is closed or disconnected, contact adhesion may occur, resulting in failure to work normally. This can be due to dust, dirt, or oxide accumulation on contact surfaces. Solutions include cleaning the contact surface or replacing the relay.

 

Poor contact:

When the contact of the relay is poor, it may cause the switching circuit to fail to open or disconnect normally. This may be due to bent, loose or contaminated contacts. Treatment measures include adjusting the contact position, tightening the contact, or cleaning the contact surface.

Relay pull or release durability issues:

This may be due to aging relay components, dust, or other external factors. Solutions include replacing relay components or performing maintenance.

 

Regular inspection and maintenance:

Regular inspection and maintenance of the power relay is very important to ensure that it is working properly and to detect problems in time. The appearance of the relay needs to be inspected to ensure that its housing is free of damage and dirt, and its internal components and connectors are visually inspected for loosening, corrosion, or damage. In addition, check the wiring terminals of the relay regularly to ensure that they are securely fastened.

 

Clean relay:

Over time, dust and impurities will accumulate inside the relay, which will affect its normal operation. Therefore, it is necessary to clean the relay regularly. When cleaning the relay, use a clean soft brush or compressed air to clean the surface and interior of the relay, taking care not to use wet materials to avoid damage to the relay.

 

Regular calibration and testing:

The accuracy of relays is essential to their proper functioning. Regular calibration and testing of relays ensures their accuracy. Calibration and testing should be carried out by professional technicians, who should use appropriate test equipment and tools to ensure the accuracy of the relay. The frequency of calibration and testing should be determined according to the type of relay and the environment in which it is used.

 

Through the above measures, the common problems of the power relay can be effectively dealt with to ensure its stable and reliable operation.

 

Action rules when a contact is opened

When the power relay contact is broken, the following brief rules should be followed:

Protect contact: Use arc extinguishing device to reduce arc damage to contact.

Check maintenance: Check contact wear regularly and clean it.

Adjust the contacts: Make sure the contacts are properly aligned and the pressure is appropriate.

Pay attention to the load: Ensure that the load current is within the rated range of the relay.

Monitor operation: pay attention to the sound and temperature of relay operation to ensure normal operation.