How to understand 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.

1. Look at 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 circuit breakers) and universal transfer switches. The latter refers to short-circuit protection devices and overload protection devices, such as the specifications and specifications of components such as electromagnetic trip units and thermal overload releases in air circuit breakers, fuses, thermal relays and overcurrent relays. In general, 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. Look at 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.

The second step: to understand the use of various relays and contactors used in the control circuit, such as the use of some special structure of the relay, should also understand their operating principles.

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 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, the actual circuit is divided into several parts according to the block diagram;

5, enter a part of the circuit, compare 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, the final realization of the circuit diagram, the understanding of the actual circuit and fault repair!