General steps, techniques, and methods for troubleshooting electrical faults

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I. General steps for troubleshooting electrical faults (1) Observe and investigate the fault symptoms: Electrical fault symptoms are diverse. For example, faults of the same type may exhibit different symptoms, while faults of different types may have the same symptoms. This consistency and diversity in symptoms add complexity to fault diagnosis. However, the symptoms of a fault are the fundamental basis for diagnosing electrical faults and represent the starting point for troubleshooting them. Therefore, it is necessary to carefully observe and analyze these symptoms, identify the most significant and typical aspects of them, and determine the time, location, and environment in which the fault occurred. (2) Analyze the cause of the fault – initially determine the scope of the fault and narrow down the location of the problem: Analyzing the cause of a fault based on its symptoms is key to carrying out electrical fault repairs. The basis of this analysis is the fundamental theories of electrical engineering and electronics; it involves a thorough understanding of the structure, principles, and performance of electrical equipment, as well as the integration of these fundamental theories with actual fault conditions. There can be many reasons for a certain electrical fault; what’s important is to identify the primary cause among them ； (3) Determine the location of the fault – Identify the fault point: Determining the location of the fault is the ultimate goal and outcome of troubleshooting electrical faults. Identifying the location of the fault can be understood as determining the faulty point in the equipment, such as a short circuit or a damaged component, or it can also refer to identifying variations in certain operating parameters, such as voltage fluctuations or imbalances among the three phases. Determining the location of the fault is carried out on the basis of a thorough examination and detailed analysis of the fault symptoms. In this process, various means and methods to be introduced below are often employed. In the process of completing the above tasks, the accumulation of practical experience plays an important role. II. Skills for Troubleshooting Electrical Faults (1) Understand circuit principles and determine a troubleshooting plan: When an electrical fault occurs in a device’s electrical system, do not rush to disassemble it. First, understand the symptoms, progression, scope, and causes of the fault. Familiarize yourself with the basic working principles of the device and its electrical system, and analyze each individual circuit. Figure out the interconnections between different stages within the circuit as well as how signals flow through it. By combining practical experience with careful consideration, develop a scientific troubleshooting plan. (2) Mechanical damage first, then the circuit: Electrical equipment is all based on electrical-mechanical principles; especially in advanced mechatronic devices, mechanics and electronics work together functionally as two parts of a whole. Often, mechanical components fail, affecting the electrical system; as a result, the functions of many electrical components are lost. Therefore, do not be deceived by surface appearances; faults in electrical systems are not always due to problems with the electricity itself – they may be caused by failures in mechanical components. Therefore, addressing the faults in the mechanical system first, and then fixing those in the electrical part, often yields twice the result with half the effort. (3) Simple first, then complex: When fixing faults, start by using the simplest and most straightforward methods that you are proficient in, and only resort to more complex and precise approaches later. When troubleshooting, first address the obvious, straightforward, and common faults. Then deal with the more difficult, unresolved issues. (4) Address common issues first, then complex problems: Electrical equipment often suffers from the same type of faults, which are known as “common issues”. Since common problems are quite frequent and ample experience exists in dealing with them, they can be resolved quickly. This allows focus and time to be devoted to addressing the rarer, more difficult, and unusual issues, thereby simplifying procedures, narrowing down the scope, and accelerating the repair process. (5) External debugging first, then internal processing: The external part refers to various switches, buttons, sockets, and indicator lights located outside the sealing elements of electrical equipment. The interior refers to the printed circuit boards, components, and various connection wires located inside the electrical equipment’s enclosure or seals. First perform external debugging, then internal processing; that is, without removing the electrical equipment, use the switches, knobs, buttons, etc. on its panel to carry out debugging and inspection in order to narrow down the scope of the fault. First, rule out faults caused by external components, and then address the faults inside the machine, trying to avoid unnecessary disassembly. (6) First, conduct measurements without power applied, and then test with power on: first inspect the electrical equipment without power, and then inspect it again with power applied. When repairing many faulty electrical devices, it is not possible to restore power immediately; otherwise, the scope of the fault could be expanded artificially, causing more components to be damaged and resulting in unnecessary losses. Therefore, before powering on the faulty machine, a resistance measurement must be taken first; only after taking the necessary measures can it be powered on for repair. (7) Public circuits first, then dedicated circuits: If the public circuits of any electrical system fail, energy and information cannot be transmitted or distributed to the individual dedicated circuits, and the functions and performance of those dedicated circuits are rendered ineffective. If the power supply of an electrical device fails, the entire system cannot function properly, and it becomes impossible to transmit energy and information to various specialized circuits. Therefore, by following the order of using common circuits first and then dedicated circuits, electrical equipment faults can be resolved quickly and accurately. (8) Summarize experience and improve efficiency: Electrical equipment failures come in a wide variety of forms, all quite unusual. After repairing any faulty electrical equipment, it is necessary to record the symptoms of the fault, its causes, the repair process, the techniques used, and any insights gained in a dedicated notebook. One should also strive to master the theoretical knowledge related to various new types of electrical equipment, understand their working principles, accumulate experience in repairs, and transform this experience into theoretical knowledge. Guided by theory and through specific analysis of each fault, it is possible to resolve faults accurately and swiftly. Only in this way can one become an expert at fixing electrical faults. III. General methods for troubleshooting electrical faults. When troubleshooting electrical faults, it is essential to combine theory with practice and conduct specific analyses based on the actual fault, but fundamental troubleshooting methods are also necessary. (1) Intuitive method: Identify abnormal conditions through \"asking, observing, listening, touching, and smelling\" in order to locate the faulty circuit and the exact point of failure. ①Question: Ask the on-site operators about the situation before and after the fault occurred. Such as whether there was overload, frequent starting and stopping before the failure occurred ； Were there any abnormal noises or vibrations when the fault occurred, as well as any signs of smoking or burning? ②Observe: Carefully examine the visual changes in the appearance of various electrical components. Check whether the contacts are melted or oxidized, whether the fuse element blowout indicator has activated, whether the thermal relay has tripped, whether the wires and cables are scorched, whether the setting value of the thermal relay is appropriate, and whether the setting current for instant operation meets the requirements. ③ Listen: Mainly listen for any differences in the sounds emitted by the relevant electrical devices before and after a fault occurs. Check whether the motor only makes a \"buzzing\" sound when starting without rotating ； Whether there is a lot of noise when the contactor coil is powered, etc. ④Touch: After a fault occurs, turn off the power supply and use your hand to touch or gently push and pull certain parts of the wires and electrical appliances in order to detect any abnormal changes. Check whether the humidity is too high on surfaces such as motor stators, self-cooling transformers, and electromagnetic wire coils ； Gently pull the wire to check if the connection is loose ； Gently push the movable mechanism of the appliance to check whether it moves smoothly, etc. ⑤Smell: After a fault occurs, turn off the power supply and bring your nose close to the motor, autotransformer, relay, contactor, insulated wires, etc., to check if there is any burnt smell. If there is a burnt smell, it indicates that the insulation layer of the electrical appliance has been damaged, usually due to faults such as overload, short circuit, or severe imbalance in the three-phase currents. (2) State analysis method: When a machine starts malfunctioning, it is only necessary to pay attention to the operating states of these components. The status is divided into very fine categories, which is more beneficial for troubleshooting electrical faults. For a device or apparatus, whose components and parts may be in different operating states, it is necessary to distinguish between these various operating states when identifying electrical faults. Taking the electrical device shown in Figure 1.2.1 as an example, although each component has only two operating states—operating and not operating, connected and disconnected—it is necessary to conduct a specific analysis to determine which state it is in. The AC contactor KM1 controls the attracting coil of the AC contactor KM2, while the operating state of the AC contactor KM1 is controlled by buttons SB1 and SB2. SB2 is open, KM1 is open, but SB2 is closed; KM1 is not necessarily closed ； SB1 closes and KM1 operates, but when SB1 is disconnected again, KM1 remains closed due to self-latching by its own auxiliary contacts. If “0” and “1” are used to represent the “off” and “on” states of SB1, SB2, and KM1, their relationship is shown in Figure 1.2.2. Among them, SB1 is usually in the off state. When SB1 is pressed (for only an instant), SB1 closes and KM1 starts to operate; SB2 is usually in the on state. When SB2 is pressed (for only an instant), SB2 turns off and KM1 stops operating. If the AC contactor KM1 cannot be disconnected, that is, if there is a fault in AC contactor KM2 causing it to change from the closed state to the tripped state, it is possible to analyze the operating status of the relevant components KM1, KM2, SB1, and SB2 in order to identify the cause of the fault. It is a method for identifying electrical faults by analyzing the operating conditions of various components, parts, and assemblies within a device or apparatus. (3) Graphic transformation method: An electrical diagram is a tool used to describe the structure, principles, and functions of electrical devices, as well as to provide information on installation, use, and maintenance. To troubleshoot electrical faults, it is often necessary to compare the actual device with the electrical diagrams. However, there are many types of electrical diagrams; therefore, it is necessary to convert one form of diagram into another for the convenience of troubleshooting. The most common one is to convert the device layout wiring diagram into a circuit diagram, and to transform a centralized layout circuit diagram into a decentralized layout circuit diagram. A device layout wiring diagram is a type of drawing that shows the approximate shape and relative positions of the devices. Such diagrams are primarily used for the installation and wiring of devices, and they are also very useful for troubleshooting electrical faults. However, it is not easy to understand the working principle and operation process of equipment and devices from such diagrams. Understanding their working principle and operation process is the basis for troubleshooting electrical faults, and it is crucial for such troubleshooting; therefore, it is necessary to convert the equipment layout wiring diagrams into circuit diagrams, which primarily describe the electrical working principle of the equipment and devices.