First, look at the general steps of the electrical diagram
1. Read the drawings in detail. After getting the drawings, first read the main title bar of the drawings and related instructions, such as the catalogue of papers, technical descriptions, electrical parts list, construction instructions, etc., combined with the existing electrician knowledge, the electrical The type, nature, and role of the diagram have a clear understanding of the overall picture and the key points to be expressed.
2, look at the schematic diagram and block diagram Because the schematic diagram and block diagram only outline the basic composition, mutual relationship and its main features of the system or subsystem, so it is necessary to look at the circuit diagram in detail, in order to understand their working principle. The schematic diagrams and block diagrams are mostly single-line diagrams. Only some of the 380/220V low-voltage distribution system diagrams are partially represented by multi-line diagrams.
3, look at the circuit diagram is the focus and difficulty of the diagram. The circuit diagram is the core of the electrical diagram, but also the most abundant and difficult to understand electrical drawings. Looking at the circuit diagram, we must first look at the graphical symbols and text symbols, understand the role of the various components of the circuit diagram, distinguish the main circuit and auxiliary circuit, AC circuit and DC circuit. Secondly, look at the picture in the order of looking at the main circuit and then looking at the auxiliary circuit. When looking at the main circuit, it is usually viewed from the bottom up, that is, starting from the electrical equipment, and then controlling the electrical components, and then looking to the power supply. When looking at the auxiliary circuit, it looks from top to bottom and from left to right, that is, first look at the main power supply, then look at each branch in turn, analyze the working conditions of the electrical components of each branch and its control relationship to the main circuit. Pay attention to the connection relationship between electrical and mechanical mechanisms. By looking at the main circuit, it is necessary to find out how the load obtains the power supply, and which electrical components pass through the electrical components to reach the load and why they pass through these electrical components. By looking at the auxiliary circuit, it is necessary to understand the composition of the auxiliary circuit, the mutual connection and control relationship between the various electrical components, and their operation. At the same time, we must understand the relationship between the auxiliary circuit and the main circuit, and then figure out the working principle and the ins and outs of the whole circuit.
4, the circuit diagram and wiring diagram to see the wiring diagram and circuit diagram to see each other, can help to see the wiring diagram. When reading the wiring diagram, it should be checked from the power supply terminal according to the terminal mark and the circuit label. Find out the connection method of the line and the circuit, and find out how each branch forms a closed loop through each electrical component. The internal and external circuits of the switchboard (screen) must be connected to each other through the terminal block. Generally speaking, there are several lines in the switchboard, and there are contacts of several lines on the terminal board, and the number lines of the external circuit can be connected only at the same number of contacts of the terminal board. Therefore, when looking at the wiring diagram, it is necessary to pay attention to the wiring of the terminal board when clearing the circuit direction inside and outside the switchboard (screen).
Second, look at the method of electrical control circuit diagram
The general method of looking at the electrical control circuit diagram is to look at the main circuit first, then look at the auxiliary circuit, and use the circuit of the auxiliary circuit to study the control program of the main circuit. The schematic diagram of the electrical control is generally divided into two parts: the main circuit and the auxiliary circuit. The main circuit is the part of the electrical control circuit through which a large current flows, including electrical components connected from the power source to the motor. The auxiliary circuit is a circuit other than the main circuit in the control circuit, and the current flowing through it is relatively small.
Three-phase wound asynchronous motor starting control
Analyze the main circuit: Regardless of the line design or line analysis, start with the main circuit. The role of the main circuit is to ensure the realization of the machine drag requirements. From the composition of the main circuit, the type and working mode of the motor or the electric appliance, control requirements such as starting, steering, speed regulation, and braking, and protection requirements can be analyzed.
Analytical control circuit: The control requirements of the main circuit are realized by the control circuit. The principle of “reforming to zero†and “successful†is used to divide the control circuit into several local control lines according to functions, from the power supply and the main signal. At the beginning, after a logical judgment, the control flow is written to express the automatic working process of the circuit in a simple and clear way.
Analysis auxiliary circuit: The auxiliary circuit includes the working status display of the actuator, power supply display, parameter measurement, illumination and fault alarm. This part of the circuit has relative independence and plays an auxiliary role without affecting the main function. Many parts of the auxiliary circuit are controlled by components in the control circuit.
Analysis of interlocking and protection links: Production machinery has high requirements for safety and reliability. In addition to reasonable selection of drag and control schemes, a series of electrical protections and necessary Electrical interlocking. In the analysis process of the electrical control schematic diagram, the electrical interlocking and electrical protection links are an important part and cannot be missed.
Overall inspection: After “normalization to zeroâ€, and gradually analyze the working principle of each partial circuit and the control relationship between the various parts, it is also necessary to check the entire control line with the method of “collecting zero as a whole†to see if there is any Missing. In particular, we should further examine and understand the relationship between the various control links from the overall perspective to achieve a correct understanding of the role of each electrical component in the schematic.
1 see the steps of the main circuit
The first step: see the electrical equipment in the main circuit. Electrical equipment refers to electrical appliances or electrical equipment that consumes electrical energy. The first thing to look at is that there are several electrical appliances, their types, uses, wiring methods and some different requirements.
The second step: to figure out what electrical components are used to control the electrical equipment. There are many ways to control electrical equipment, some are controlled directly by switches, some are controlled by various starters, and some are controlled by contactors.
Step 3: Understand the control and protection devices used in the main circuit. The former refers to control components other than conventional contactors, such as power switches (transfer switches and air, universal transfer switches. The latter refers to short circuit protection devices and overload protection devices, such as electromagnetic trips and thermal overloads in air circuit breakers. The specifications and specifications of the components of the trip unit, fuses, thermal relays, and overcurrent relays. Generally, after analyzing the main circuit as described above, the auxiliary circuit can be analyzed.
Step 4: Look at the power supply. To know the power supply voltage level, whether it is 380V or 220V, is it from the busbar busbar power supply or the power distribution panel, or from the generator set.
2 see the steps of the auxiliary circuit
The auxiliary circuit includes a control circuit, a signal circuit, and a lighting circuit. Analyze the control circuit. According to the control requirements of each motor and the executing electric appliance in the main circuit, the other control links in the control circuit are found one by one, and the control circuit is turned into zero, and divided into several local control lines according to different functions for analysis. If the control circuit is more complicated, the circuits that are not closely related to the control such as illumination and display can be excluded to concentrate on the analysis.
The first step: look at the power supply. First look at the type of power supply. Is it AC or DC? Second. It is necessary to see where the power supply of the auxiliary circuit is connected, and its voltage level. The power supply is generally connected from the two phase lines of the main circuit, and its voltage is 380V. It is also connected from one phase line and one zero line of the main circuit, and the voltage is single phase 220V; in addition, it can also be used from a dedicated isolated power supply. The transformer is connected, and the voltage is 140, 127, 36, 6.3V, and the like. When the auxiliary circuit is DC, the DC power supply can be connected from the rectifier, the generator set or the amplifier, and the voltage is generally 24, 12, 6, 4.5, 3V, and the like. The coil rated voltage of all electrical components in the auxiliary circuit must be the same as the auxiliary circuit power supply voltage. Otherwise, the circuit components do not operate when the voltage is low; when the voltage is high, the electrical component coils are burned out.
Step 2: Understand the use of various relays and contactors used in the control circuit. If some special structure relays are used, they should also understand their action principle.
The third step: According to the auxiliary circuit to study the action of the main circuit. After analyzing the above contents and combining the requirements in the main circuit, the operation process of the auxiliary circuit can be analyzed. The control circuit is always drawn between two horizontal power lines or two vertical power lines in the order of action. Therefore, it is possible to analyze from left to right or from top to bottom. For complex auxiliary circuits, the entire auxiliary circuit forms a large loop in the circuit. In this large loop, it is divided into several independent small loops, each of which controls an electrical device or an action. When a small loop forms a closed loop and a current flows, the electrical components (contactors or relays) in the loop operate, and the electrical equipment is connected or the power is removed. In the auxiliary circuit, the circuit is usually turned on by a button or a transfer switch. The analysis of the control circuit must be carried out at any time in conjunction with the action requirements of the main circuit. Only after fully understanding the requirements of the main circuit for the control circuit can the operating principle of the control circuit be truly grasped, and the operating principle of each part cannot be viewed in isolation, but should be noted. Whether there is a mutual constraint relationship between the various actions, such as interlocking between the positive and negative phases of the motor.
Step 4: Study the relationship between electrical components. All electrical components in the circuit are not isolated but are interconnected and mutually constrained. This mutual control relationship is sometimes manifested in a loop, sometimes in several loops.
Step 5: Study other electrical equipment and electrical components. Such as rectifier equipment, lighting, etc.
In summary, the main points of the line-checking method of the electrical control circuit diagram are:
(1) Analyze the main circuit. From the main circuit manpower, according to the control requirements of each motor and the execution of electrical appliances, analyze the control content of each motor and the execution of electrical appliances, such as motor start, steering control, braking and other basic control links.
(2) Analyze the auxiliary circuit. Look at the auxiliary circuit power supply, to understand the role of the various electrical components in the auxiliary circuit and their mutual constraints.
(3) Analyze the interlocking and protection links. Production machinery has high requirements for safety and reliability. To achieve these requirements, in addition to reasonable selection of drag and control schemes, a series of electrical protections and necessary electrical interlocks are also set in the control lines.
(4) Analysis of special control links. In some control lines, some special links that are not closely related to the main circuit and the control circuit and are relatively independent are also provided. Such as product counting device, automatic detection system, thyristor trigger circuit, automatic temperature adjustment device. These parts tend to be a small system. The method of reading and analyzing can refer to the above analysis process, and use the knowledge of electronic technology, communication technology, automatic control system, detection and conversion, etc., to analyze one by one.
(5) Overall inspection. After the transformation to zero, and gradually analyze the working principle of each partial circuit and the control relationship between the various parts, it is also necessary to use the method of collecting zeros as a whole to check the entire control circuit to see if there is any omission. Finally, we should further examine and understand the relationship between the various control links from the overall perspective to achieve a clear understanding of the role, working process and main parameters of each electrical component in the circuit diagram.
1 First, you need to know how the device is operated, used, and working.
2 Look at the circuit block diagram of this device, figure out the connections, relationships, and interactions between the block diagrams, and understand the analysis block diagram with the operation, use, and work of the device you know;
3 Enter the specific circuit of a block diagram. Look for the power supply of the block diagram, the input and output of the signal...
4 Open the actual circuit of the device, first find the corresponding part of the circuit corresponding to the block diagram, and divide the actual circuit into several parts according to the block diagram;
5 Enter a part of the circuit, look at the circuit diagram, find the position of the corresponding components, and constantly understand the function, work, and possible fault performance of the main components in the actual circuit;
6 Finally realize the circuit diagram, the understanding of the actual circuit and fault repair!
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