The sixth branch of Hunan XX Co., Ltd. ×××××
The duty of the maintenance electrician is to ensure the normal operation of the motors driving various production machinery in the factory and their electrical control systems, production and lighting systems. As a maintenance electrician, in addition to reasonable installation, good debugging and daily maintenance inspection of equipment and circuits, he should also be able to quickly find out the cause of the fault and deal with it correctly when it happens, which is an important guarantee to ensure the normal operation of the equipment.
Keywords: electrical troubleshooting methods troubleshooting steps
In practical work, electrical faults occur in a wide range, involving all parts of the electrical system, and the faults are ever-changing and random. Troubleshooting methods can only be based on specific failures.
Depending on the situation, there is no strict and fixed touch mode, which sometimes confuses many people. In the process of troubleshooting, they often take many detours and even cause great losses. Then, as a maintenance electrician, when encountering a fault, he should be able to quickly find out the cause of the fault and deal with the fault point reasonably and correctly, which is of great significance for improving labor production efficiency, reducing economic losses and safe production. As a maintenance electrician, you should not only have high knowledge and skills, but also have the ability to train and guide senior engineers and maintenance personnel below. I have been engaged in this profession for nearly 6 years, and I have gradually explored and summarized some experiences. Based on my own work (taking B20 12A planer as an example), I will talk about my understanding of troubleshooting and discuss with my colleagues in order to learn from each other, promote and improve.
(A) the basis of troubleshooting
To completely eliminate the fault, you must know the cause of the fault; In order to find out the cause of the fault quickly, in addition to accumulating experience in work, it is more important to analyze and explain the cause of the fault theoretically, then guide your own operation with theory and use various methods flexibly to eliminate the fault.
(1) must have some professional theoretical knowledge.
Many electrical faults can only be truly understood and recognized by relying on professional theoretical knowledge. Maintenance electrician is more theoretical than other types of work, and sometimes a lot of work can't be carried out without theoretical guidance. In practical work, we often spend more time thinking than doing. Once the fault point is found, it is relatively simple to maintain.
(2) Understand the movement form of the equipment
Requirements for electricity, understanding and mastering the electrical working principle of equipment, understanding the movement form of equipment and the requirements for electricity are the basis for understanding the electrical working principle of equipment. Mastering the electrical working principle skillfully and comparing the electrical control characteristics of equipment are very important foundations for troubleshooting. For example, the electrical control system of A series planer includes not only relay control of AC and DC motors and appliances, but also continuous feedback control and disturbance compensation feedforward control. It is a compound control system, which summarizes the main contents of electrical control technology and has certain typicality, comprehensiveness and complexity. If you master the electrical working principle of this equipment, you can better troubleshoot and draw inferences from other equipment.
(3) Understand the specific location of each electrical component in the equipment and the layout of the circuit.
Realizing one-to-one correspondence between electrical schematic diagram and actual wiring is the basis of improving troubleshooting speed. By doing so, we can have a better understanding of the equipment, select effective test points when troubleshooting, prevent misjudgment and narrow the fault range.
(B) the general method of troubleshooting
With a certain theoretical basis, we have mastered the working principle of the equipment, made full preparations for troubleshooting, and needed some means to effectively analyze and find out the fault points in operation, which is a general method for troubleshooting.
(1) resistance method
Resistance method is a commonly used measurement method. Usually, it refers to a method to measure whether circuits, contacts, etc. are normal. Use the multimeter to turn it off or off; Sometimes a multimeter or a bridge is used to measure whether the resistance of the coil meets the nominal value, or an megger is used to measure the insulation resistance between phase and ground. Pay attention to the selection of measuring range when measuring (generally choose a lower gear when measuring channels) and check the instrument; Pay attention to whether there are other circuits to avoid misjudgment, and pay more attention to the prohibition of live measurement.
(2) Voltage method
Refers to the method of measuring the voltage value in the circuit with the corresponding voltage block of multimeter. Usually, when measuring, sometimes the voltage of power supply and load is measured (that is, the load is always included between two meters), and sometimes the open circuit voltage is measured to judge whether the circuit is normal or not. Pay attention to the gear position of the instrument when measuring, choose the appropriate range, and pay attention to the positive and negative polarity when measuring DC. This is also a common method.
(3) Current methods
Current method is a method to determine the cause of failure by measuring whether the current in the circuit meets the normal value. In the weak current circuit, the current block of ammeter or multimeter is often connected in series to measure in the circuit. High-voltage circuits are usually detected by clamp ammeter.
(4) substitution method
When the equipment is suspected to be faulty, but it is uncertain and there is a substitute, the replacement test can be carried out to see if the fault is restored.
(5) Short connection method
It is suitable for low voltage and small current circuits, and the points suspected of short circuit are short-circuited by wires for testing. But it must be ensured that short circuit will not cause short circuit, and once short circuit works, it will not cause harm.
(6) Direct test method
If you know the cause or experience of the fault, the probability of frequent faults is high, and there are some special faults, you can directly check the suspected fault points.
(7) Instrument test method
With the help of various instruments and meters, various parameters are measured, such as observing the changes of waveforms and parameters with oscilloscopes, so as to analyze the causes of faults, which are mostly used in weak current circuits.
(8) phase-out method
If there is a short circuit, some circuits can be cut off step by step to determine the fault range and fault point.
(9) Adjustment parameter method
In some circuits, the components are intact and the circuit wiring is good, but some physical quantities (such as time, displacement, current, resistance value, temperature, feedback signal strength, etc.). ) improper adjustment, resulting in the system can not operate normally. At this time, it should be adjusted according to the electrical working principle and the specific situation of the equipment.
(10) comparative analysis judgment method
It compares, analyzes and judges according to the working principle of the system, the action procedure of the control link and the logical relationship between them, combining with the fault phenomenon, reducing the measurement and inspection links and quickly judging the fault range. For example, one of the control circuits in the two places is in normal control, which means that there must be no problem with the power supply, load and public circuit. Through analysis, comparison and judgment, we can reduce the detection links, narrow the fault range and improve the speed of troubleshooting. It is suitable for directly judging the fault range or fault point of some circuits, and should also run through the whole troubleshooting process.
The above commonly used methods can be used alone or in combination, and should be used flexibly according to the specific situation.
(2) General steps of troubleshooting
Although there is no fixed mode of troubleshooting, in general, there are certain rules.
1, fully understand the situation when the fault occurs.
1), ask the operator in detail about the fault phenomenon of the equipment.
2) By looking, listening, smelling and touching, judge whether there are special phenomena such as cracking, noise, peculiar smell and overheating.
3) In the case of no danger, power on for trial operation.
Through the above understanding, the fault can be accurately determined. This is the basis of fault analysis. If the fault phenomenon is not clear, it will lead to the deviation of fault analysis.
2. Analyze the fault and determine the fault range.
According to the fault phenomenon, combined with the working principle and control characteristics of the equipment, determine the fault range, whether it is electrical fault or mechanical fault, DC circuit or AC circuit, main circuit or control circuit and auxiliary circuit, power supply part or load part or control circuit part and whether it is the circuit reason.
Improper parameter adjustment and so on.
3. Narrow the fault range through detection, analysis and judgment.
The process of troubleshooting is often a process of gradually narrowing the fault range through analysis, detection and judgment. Flexible use of the above-mentioned "general method of troubleshooting", gradually narrow the scope of the fault until the fault point is found.
4, follow certain principles in the process of troubleshooting.
(1) Think before you do it.
From the determination of fault phenomena to the analysis, detection and judgment of faults, we should keep a clear head. "strategizing, winning a thousand miles", correct analysis can play a multiplier effect. Don't pick up the meter and take it apart as soon as it breaks down. To develop a good habit of analysis and judgment, every measurement should have a clear purpose, that is, what the measurement results can explain.
(2) In general, the analysis and detection sequence when troubleshooting is based on the action sequence of the equipment.
On this premise, check the power supply first, and then check the circuit and load; Check the common circuit before checking each branch circuit; Check the control circuit first, then check the main circuit; First, check the parts that are easy to measure (for example, in the electric box); Then check the parts that are difficult to detect (such as devices on the equipment). For example, on the B20 12A planer, the planer table can neither "advance" nor "step". Analysis: this phenomenon shows that the motor expander, DC generator, DC motor and exciter are all working normally; The motor set works normally; AC control power supply is normal; The common part of AC circuit and DC circuit in the automatic circulation loop of planer is normal; The male part of DC circuit of planer stepping back is normal. The fault range should be:
1) AC circuit, "planer stepping, forward rotation control" circuit.
2) DC circuit, the stepping and advancing branches of planer (excluding the common branches of backward and backward).
After determining the fault range, according to the working principle, the work of DC loop is mainly controlled by the contact of intermediate relay.
System, and the coil of the intermediate relay is in the AC loop, so check the AC loop first. When checking the AC circuit, you should first observe the action of the relay. If you press the step button and the forward button, the relay coil will not be energized. The voltage method or resistance method can be used to check the connection between the coil of the forward relay, the interlocking point of the backward relay, the normally closed contact of the backward button, and the normally closed contact of the forward and backward travel switch and the wires. Post-inspection step
Button, forward button, normally open contact of automatic circulation relay and their connecting wires. After confirming that the AC circuit is normal, repair the DC circuit. First, observe whether the intermediate relay coil is electrified before the supplied time relay coil is electrified, so as to judge whether the contact and connection of the intermediate relay are good, and measure whether the DC voltage at the back stage of the contact of the time relay is normal, so as to judge whether the time relay coil is electrified. After these parts are normal, if the fault still exists, the "step" and "forward" branches in DC circuit can be measured by resistance method and voltage method respectively, and
(3) When measuring a branch, it can be measured and checked step by step from the power supply to the load.
After proficiency, you can directly detect from some positions in the middle of the circuit, which can quickly narrow the fault range until you find the fault point.
(4) Special faults should be handled specially.
There is no need to check step by step, such as B20 12A gantry planer, which automatically stops at the original position after each start. In the starting control circuit of the motor set, the normally closed contact of the thermal relay is disconnected, and the automatic circulation circuit of the planer and the contact of the lubricating pressure relay are not connected, so these two parts can be detected first.
5. Further narrow the fault range, find out the fault point and eliminate the fault point.
The treatment of fault points should be reasonable and reliable, and the fault should be eradicated. For example, when the thermal relay acts, it is necessary not only to reset the contact of the thermal relay, but also to find out the cause of overload and deal with it; Melting, not only to replace the new melt, but also to find out the cause of melting and deal with it. At the same time, it should also explain the problems that should be paid attention to to to the relevant personnel.
The above is my own experience in troubleshooting electrical equipment. Due to the limited level, there are inevitably some shortcomings. Please correct me.
References:
Li Jingmei. Electric drive control circuit and skill training [M]. Beijing: China Labor and Social Security Publishing House, 200 1.
[2] Liu Guangyuan. How to find the electrical fault [M]. Beijing: Machinery Industry Press, 2003.
Zhou Xizhang. Diagnosis and maintenance of machine tool circuit faults [M]. Beijing: Machinery Industry Press, 2003.
Wang. Maintenance electrician (technician) [M]. Jinan: Shandong Science and Technology Press, 2002.