The voltage electrical equipment with contact action mainly consists of three parts: contact system, electromagnetic system and anti-isolation device. It is also the focus of overhaul.
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1, the fault of the contact fault detection contact is generally contact overheating, welding and so on. The main reason for contact overheating is insufficient contact pressure, surface oxidation or uncleanness, and insufficient capacity. The main reason for contact welding is that the contact generates a large arc when it is closed, and the contact is severely beaten.
Check the oxidation of the contact surface and the presence or absence of dirt. The contacts are dirty and have been cleaned with gasoline.
The oxide layer of the silver contact not only has good electrical conductivity, but also is reduced to metallic silver during use, so it can be repaired.
If the copper contact has an oxide layer, it can be flattened with oil or lightly scraped off the oxide layer on the surface with a knife.
Observe the surface of the contact surface for burns and singeing. The copper contact singe can be finished with a slick or a knife. The surface of the refurbishing contact does not have to be excessively smooth, and it is not allowed to be repaired with an abrasive cloth to prevent the residual sand from being embedded in the contact when the contact is closed, resulting in poor contact. However, the silver contact singeing does not have to be refurbished.
If the contacts are welded, the contacts should be replaced. If the contact capacity is not enough, the appliance with a large capacity should be selected for replacement.
Check the contacts for looseness and tighten if necessary to prevent the contacts from jumping. Check the contact for mechanical damage to deform the spring, resulting in insufficient contact pressure. If so, adjust the pressure to make the contacts in good contact. The empirical measurement method of contact pressure is as follows: the initial pressure is measured, a paper is placed between the bracket and the movable contact. The treaty is 0.1 mm, the width is wider than the contact, and the paper strip is pressed under the action of the spring. Use a hand-drawn paper strip. When the paper strip can be pulled out and has a strong sense of force, it can be considered that the initial pressure is more suitable. The final pressure is measured, the paper strip is sandwiched between the moving and static contacts, and the contact is energized at the electrical appliance. After that, pull the paper strip in the same way. When the paper strip can be pulled out, the final pressure is considered to be suitable. For large-capacity electrical appliances, such as 100A or more, when the paper strip is pulled in the same way, when the paper strip is pulled out, there is a tear phenomenon, and the initial and final pressures are considered to be suitable.
The measurement of the above contact pressure works well in multiple repair tests. It can be carried out normally. If the measured pressure value cannot be restored by the adjustment spring, the spring or contact must be replaced.
2. Troubleshooting of the electromagnetic system Due to poor contact of the end faces of the moving and static iron cores, skew of the iron core, damage of the short-circuit ring, and too low voltage, the armature noise is large, and even the coil is overheated or burned.
(1) The armature is noisy. When repairing, the coil should be removed, and the contact surface between the static iron core and the static iron core should be clean and free of oil. If it is not smooth, it should be flattened or smoothed; if there is oil, it should be cleaned with gasoline.
If the moving iron is skewed or loose, it should be corrected or tightened.
Check the short-circuit ring for breakage. If the breakage should be replaced with a copper plate according to the original size, or the thick copper wire is tapped into a square section, and the original size is installed.
(2) The armature is not released immediately after the electromagnetic coil is de-energized. The main reasons for this failure are: the moving part is stuck;
The size of the core air gap is too large; the spring is fatigue deformed, the elastic force is insufficient, and the iron core contact surface is oily. After disassembly and refurbishment, an air gap of 0.02-0.03 mm is left between the end face of the core and the bottom end of the core, or the spring is replaced.
(3) Coil troubleshooting. The main fault of the coil is that the coil is too hot to burn out due to the excessive current it passes.
This kind of fault is usually caused by the insulation damage of the coil, the power supply voltage is too low, the contact between the moving and static iron core is not tight, and the coil current is too large, and the coil is overheated and burned.
If the coil is burnt due to a short circuit, the wire diameter and number of turns can be measured from the burnt coil when rewinding. The wire diameter and number of turns of the coil can also be found on the nameplate or manual. According to the cross section of the iron core, the wire mold is made. After the coil is wound, it is placed at 105-110 °C.
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If the coil is shorted, there are not many turns. The short-circuit point is close to the head of the coil, and the rest is intact. The power should be cut off immediately to prevent the coil from being burnt. If there is no vibration mechanical noise after the coil is energized, check the connection point of the coil lead-out line and do not fall off. Check whether the coil is broken or burned with a multimeter. If there is vibration and noise after power-on, check whether the active part is stuck, static or moving. Is there a conductor between the cores, and the power supply voltage is too low. To be treated differently and deal with in a timely manner.
3. Inspection of the fire extinguishing device Remove the arc extinguishing cover, check the integrity of the arc extinguishing sheet and remove the smoke marks and metal fines on the surface, and the outer casing should be intact.
If the arc extinguishing cover has broken cracks, it should be replaced in time. In particular, the original electrical appliance with an arc-extinguishing hood is never allowed to use a phoenix to prevent short-circuiting without an arc-extinguishing hood.
There are many types of low-voltage electrical appliances commonly used. The above are some representative and most commonly used methods of electrical faults and their essentials. They are bypassed and have certain commonalities for the maintenance of other electrical appliances.