How beginner electricians can quickly understand electrical control circuit diagrams

Electrical control is a method of automatically or remotely controlling mechanical equipment with the help of the structure and characteristics of various electrical components. According to external signals and requirements, electrical components use manual or automatic circuit disconnection and intermittently or continuously change electrical parameters to achieve switching, control, protection, detection and regulation of circuits or non-electrical objects. A key point in reading electrical diagrams is to master the structural principles of components. For example, when the coils of contactors, relays, and intermediate relays are energized, they drive the armature to close, causing their main and auxiliary contacts to make opposite changes (the originally disconnected ones are connected, and the originally connected ones are disconnected). Turn on or off the main circuit and other circuits to achieve control; another example is that after the coil of a time relay is energized, its normally open and normally closed contacts are not turned on or off immediately, but delayed for a period of time before they can be turned on or off. When the circuit is opened, the length of the delay time can be adjusted and changed. As long as you understand the characteristics of these components, the electrical diagram will be easy to understand.

When reading electrical diagrams, you should look at the main circuit first, then the control circuit. When looking at the main circuit, we usually look at it from bottom to top, that is, starting from the electrical equipment, going through the control components and protection components in order to see the power supply. By looking at the main circuit, you need to understand how the electrical equipment obtains power, which components the power passes through to reach the load, and what the specifications, models, and functions of these components are.

The electrical control circuit is divided into main control circuit (primary circuit, main circuit) and auxiliary circuit (secondary circuit, control circuit). The main circuit is generally drawn above or on the left side of the drawing with a thick solid line. It is connected to the three-phase power supply and connected to the load. It allows large currents to pass through and is directly controlled by the auxiliary circuit; the auxiliary circuit is controlled by weaker currents and is controlled by Thin solid lines are drawn below or to the right of the drawing to control the main circuit action.

You should look at it from top to bottom and from left to right, that is, look at the power supply first, then look at each circuit in turn, and analyze the working conditions of the components in each circuit and their control relationship with the main circuit. When looking at the control circuit, it is necessary to understand the composition of the circuit, the connection between the components (such as sequence, interlocking, etc.) and the control relationship, and under what conditions the circuit forms a path or a break, how the control circuit controls the work of the main circuit, So as to understand how the whole system works.

The figure below shows the schematic diagram of motor starting control.