First, several maintenance examples of common voltage electrical faults
1, voltage circuit breaker failure
If the contact is overheated, it can smell the distribution control cabinet. After checking, the moving contact is not fully inserted into the static contact, and the contact pressure is not enough, resulting in a decrease in the switch capacity and causing the contact to overheat. At this point, adjust the operating mechanism so that the moving contact is fully inserted into the static contact.
When the power is on, the arc flashes, and it is checked that the load is too long and the contact is loose. It is necessary to pay attention to safety when overhauling this fault, and to prevent the damage of the arc to people and equipment. After the load and contacts are overhauled, the load can be checked for operation until the load is normal. This fault must pay attention to the routine maintenance work of the equipment, so as not to cause unnecessary harm.
1, the contactor failure
The contact is out of phase, because the contact of a certain phase is not good or the screw on the terminal is loose, the motor is out of phase, and the motor can rotate, but it will beep. Should be stopped for maintenance immediately.
The contact is welded, and the “stop” button is connected, the motor does not stop, and there is a possibility of a click. This kind of fault is caused by the large current caused by the overload current of the two-phase or three-phase contacts. The power should be cut off immediately, and the contactor should be replaced after checking the load.
The energized armature does not pick up. If the power is checked without vibration and noise, it means that the moving part of the armature is stuck, but the coil is broken. The detachable coil is re-wound according to the original data and then dipped in the paint.
3, thermal relay failure
The thermal power equivalent element is blown. If the motor fails to start or there is a click when starting, it may be that the fuse in the thermal element of the thermal relay is blown. The cause of such a fault is that the operating frequency of the thermal relay is too high, or an overload occurs on the negative side. After troubleshooting, replace the appropriate thermal relay, and then re-adjust the settings.
The thermal relay is “false”. The causes of such failures generally include the following: the setting value is too small, so that the operation is not overloaded; the motor starting time is too long, so that the thermal relay operates during the starting process; the operating frequency is too high, so that the thermal element is often subjected to an impact. Re-adjust the settings or replace the appropriate thermal relay solution.
The thermal relay does not operate. This type of fault is usually caused by a large current setting value, so that the overload does not operate for a long time, and the setting current should be adjusted according to the load operating current.
The thermal relay is used for a long time and should be regularly verified for its operational reliability. When the thermal relay is tripping, the bimetal should be cooled and then reset. Press the reset button to force it too hard, otherwise the operating mechanism will be damaged.
Second, the troubleshooting of common voltage electrical appliances and its essentials
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.
1. Troubleshooting of contacts
Contact failures generally include contact overheating, fusion welding, and the like. 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 excessive current flow.
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 cores 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.
In an oven for 3 hours, cool to 60-70 ° C to soak 1010 asphalt paint, you can also use other insulating paint. After dripping the paint, it is dried in an oven at a temperature of 110-120 ° C, and can be used after cooling to room temperature.
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. Overhaul of 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. 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.
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