Overhaul of common faults in relays - Solutions - Huaqiang Electronic Network

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A relay is an electrical device that turns on or off a control circuit to complete a control or protection task according to a signal input from the outside, such as an electrical quantity (voltage, current) or a non-electrical quantity (heat, time, speed, etc.). There are three basic parts, namely the sensing mechanism, the intermediate mechanism and the actuator. The article describes the troubleshooting methods for their failure.
1 Inspection of the sensing mechanism For the electromagnetic (voltage, current, intermediate) relay, the sensing mechanism is the electromagnetic system. The failure of the electromagnetic system is mainly concentrated in the coil and the moving and static core parts.
(1) Coil fault repair coil fault is usually damaged by coil insulation; short circuit or grounding is formed by mechanical injury; because the power supply voltage is too low, the contact between the moving and static iron core is not tight, so the coil current is too large, the coil heats up and burns . When repairing, rewind the coil. If the armature does not pick up after the coil is energized, it may be that the coil lead-out line is disconnected, causing the coil to open. Check the drop off and solder it.
(2) Iron core failure repair core failure mainly after the power is applied, the armature cannot be sucked up. This may be caused by a broken wire, a foreign object between the moving and static iron cores, and a low power supply voltage. Repair should be done differently.
After power-on, the armature is noisy. This may be due to uneven contact surfaces of the moving and static cores or oil contamination. When repairing, remove the coil, level or smooth the contact surface; if there is oil, it should be cleaned.
The noise may be caused by a short circuit or a ring break, and repair or replacement of a new short circuit ring.
After the power is cut off, the armature cannot be released immediately. This may be caused by the moving iron core being stuck, the iron core air gap being too small, the spring strain and the iron core contact surface being oily. During maintenance, it should be treated differently for the cause of the fault, or adjust the air gap to protect it at 0.02 ~ 0.05mm, or replace the spring, or use gasoline to clean the oil. For thermal relays, the sensing mechanism is a thermal element. Common faults are burnout of the thermal components, or malfunction and non-action of the thermal components.
(1) The thermal element burned out. This may be due to a short circuit on the load side or a high frequency of operation of the thermal element. The heating element should be replaced during maintenance and the setting value should be readjusted.
(2) The thermal element malfunctions. This may be caused by the setting value being too small, not being overloaded, or having strong impact and vibration in the use case, causing the action mechanism to loosen and trip and causing malfunction.
(3) The thermal element does not operate. This may be due to the setting value being too small to cause the thermal element to lose its overload protection function. The tuning current should be adjusted according to the load operating current during maintenance.
2 Actuator maintenance Most relay actuators are contact systems. Through its "on" and "off", to complete certain control functions. Faults in the contact system generally include contact overheating, wear, welding, and the like. The main cause of contact overheating is insufficient capacity, insufficient contact pressure, surface oxidation or uncleaning; the main cause of increased wear is that the contact capacity is too small, the arc temperature is too high, and the contact metal is oxidized; The main reason for welding is that the arc temperature is too high, or the contact is severely beaten. The inspection sequence of the contacts is as follows:
(1) Open the cover and check the surface of the contact.
(2) If the surface of the contact is oxidized, the silver contact may not be repaired, and the copper contact may be smoothed with a slick or a small knife to gently scrape off the oxide layer on the surface.
(3) If the contact surface is not clean, it can be cleaned with gasoline or carbon tetrachloride.
(4) If the contact surface has burn marks, the silver contacts may not need to be refurbished, and the copper contacts may be refurbished with a slick or a knife. It is not allowed to use sand cloth or sandpaper for refurbishment to avoid residual sand and cause poor contact.
(5) If the contacts are welded, the contacts should be replaced. If the contact capacity is too small, replace the relay with a larger capacity.
(6) If the contact pressure is not enough, adjust the spring or replace the spring to increase the pressure. If the pressure is still not enough, the contacts should be replaced.
3 Maintenance of the intermediate mechanism (1) For the air type time relay, the middle mechanism is mainly the air bag. The common fault is that the delay is not allowed. This may be because the airbag is not tightly sealed or leaking, so that the action delay is shortened or even delayed; it may also be that the air passage of the airbag is blocked, so that the action delay becomes longer. When repairing, the former should be reassembled or replaced with a new airbag. For the latter, the air chamber should be dismantled to remove the blockage.
(2) For speed relays, the bakelite pendulum is an intermediate mechanism. If the motor can't brake and stop when the brake is reversed, it may be that the bakelite pendulum is broken. It should be replaced during maintenance.
Summarizing the common troubleshooting methods of relays is conducive to the good operation of power equipment and systems, and can also provide reference experience for peers.