In the control circuit of low-voltage electrical appliances, there are simple low-voltage components such as: buttons, safe, etc.; There are also slightly messy low-voltage electrical control components, such as circuit breakers, touch devices, time relays, thermal relays and other simple components, which makes it necessary to diagnose and analyze the cause of the problem.
The cause of common low-voltage electrical problems is confirmed
Vacuum circuit breakers
As a new type of circuit breaker, vacuum circuit breaker has many advantages compared with the previous less oil circuit breaker, magnetic blowing circuit breaker, etc., especially in recent years, the influx of the latest foreign vacuum circuit breaker and the continuous innovation of domestic manufacturers, so that the vacuum circuit breaker structure type compared with the past, has undergone great changes, resulting in the use, protection and maintenance of the new vacuum circuit breaker, many staff will feel prickly, especially if something goes wrong, it is helpless.
Whether there is a problem with the vacuum circuit breaker can be judged by whether it can accurately close and open and reliably maintain the closing and opening position. Faults in the main circuit can be found and eliminated from the routine maintenance and protection of the circuit breaker.
The main causes of common problems are as follows:
No energy storage. Failure to store energy is one of the more common problems of vacuum circuit breakers, especially the energy storage organization driven by ratchet and pawl, which has a high probability of failure. In order for the energy storage organization to complete the energy storage action, it mainly depends on the three links of the energy storage motor, the drive organization and the positioning parts. Firmly grasp these 3 links, it is very simple to find out the crux of the problem.
There is no closing action. The occurrence of no closing action is mainly related to whether the closing solenoid is engaged, whether the energy storage is in place, and whether the positioning part is normal.
Void. If there is a closing action but the brake cannot be closed, it is called a void closing. When analyzing such faults, the first step should be to analyze the closing hold (lock), and then analyze whether it is related to the energy storage part.
No opening. It should be emphasized here that when the circuit breaker is rejected, empty and closed, etc., before analyzing and repairing the main body of the circuit breaker, it is necessary to fully judge whether the cause is in the control and secondary components such as auxiliary switches, terminal strips, etc., and then carry out the analysis and diagnosis of the circuit breaker.
Toucher
Touchers are divided into AC touchers, DC touchers, intermediate frequency touchers, AC vacuum touchers, etc., during which AC touchers are the most widely used. AC touch device is a kind of electromagnetic automatic switch, which is mainly used for long-distance control of motors and other loads with large power and frequent starting, and is the most commonly used control electrical appliance in the power system; It is easy to cause equipment and personal accidents when it is a problem, and it must be eliminated as a result.
The common problems of AC touchers are that after the coil is energized, the toucher does not operate or does not operate normally, and after the coil is powered off, the toucher does not release or delays the release.
After the coil is energized, the toucher does not operate or does not operate normally, and the primary causes of the problem are:
Coil control line breaking: see if the terminal is broken or loose, if there is a broken wire, replace the corresponding wire, if there is a loose, fasten the corresponding terminal.
Coil damage: Use a multimeter to measure the resistance of the coil, if the resistance is +∞, replace the coil.
The coil voltage rating is higher than the line voltage. Replace it with a coil that adapts to the voltage of the control line.
After the coil is powered off, the toucher is not released or delayed, and the primary causes of the problem are:
There is no air gap in the column in the magnetic system, and the remanence is too large. File part of the pole surface at the remanence gap to make the gap 0.1-0.3mm, or connect a 0.1uF capacitor in parallel at both ends of the coil.
The core of the enabled toucher has an oily appearance or is greasy after a period of use. Wipe the anti-rust grease on the surface of the core, and the surface of the core should be flat, but it should not be too light, otherwise it is easy to constitute a delayed release.
The contact has poor anti-fusion welding function, when the motor is started or the line is short-circuited, the high current makes the contact, the head is welded firmly and can not be released, during which the sterling silver contact is more easily melt welded.
Relays
Relay is an automatic device, which is responsible for ensuring the safe and reliable operation of the power system in the power system, which monitors the operation status of the system at any time, and can quickly find the problem, and then selectively cut off the problem part through the circuit breaker.
The common types of relay problems and the analysis of diagnosis are as follows:
Contact erosion. At the moment of disconnecting the rational load, the magnetic energy it accumulates will generate a high back-EMF at both ends of the contact, and the air gap between the breakdown contacts will constitute a spark, and electric erosion will occur, resulting in a concave touch surface, causing poor touch, or the two contacts will be glued together and cannot be separated, thus constituting a short circuit. To avoid the electrical corrosion between the contacts, it can be done by setting up a resistive spark circuit and a resistor-capacitance fire extinguishing circuit.
Dust accumulation at the contacts. Dust and dirt will be deposited on the contacts of the relay, which will cause a black oxide film to be formed on the surface of the contact, resulting in poor touch of the relay, so the contact needs to be cleaned regularly, and carbon tetrachloride liquid can be used, which can ensure the excellent touch function of the contact.
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