Function and composition of electrical control system

major function

In order to ensure the reliability and safety of primary equipment, many auxiliary electrical devices are needed to serve it. The combination of several electrical components that can achieve a certain control function is called a control circuit or secondary circuit. These devices should have the following functions:

(1) Automatic control function. High voltage and high current switchgear has a large volume and is generally used to control the opening and closing of operating systems. Especially when the equipment malfunctions, it needs to automatically cut off the circuit in order to have a set of automatic control electrical operating equipment and power supply equipment for automatic control.

(2) Protection function. Electrical equipment and circuits may malfunction during operation, with current (or voltage) exceeding the allowable operating range and limits of the equipment and circuits. This requires a set of protective equipment to detect these fault signals and automatically adjust (disconnect, switch, etc.) the equipment and circuits.

(3) Monitoring system functionality. Electricity is invisible to the eyes, and it is impossible to distinguish whether a device is powered on or off from its appearance. This requires companies to set up various network audiovisual signals, such as lights and sound systems, to analyze and monitor the electrical information of a device.

(4) Measurement function. Light and sound signals can only qualitatively display the working status of the device (with or without electricity). If we want to quantitatively understand the working status of electrical equipment, we need various instruments to measure the parameters of devices and circuits, such as voltage, current, frequency, and power.

In the operation and monitoring of equipment, traditional operating components, control appliances, instruments, and signals can be replaced by computer control systems and electronic components, but there is still a certain range of applications in small devices and local control circuits. This is also the basis for implementing microcomputer automatic control in circuits.

system composition

The basic circuit of commonly used control circuits consists of the following parts.

(1) Power supply circuit. The power supply of the power supply circuit includes AC380V and 220V, etc.

(2) Protect the control circuit. The power supply for protecting (auxiliary) circuits includes various types such as single-phase 220, 36V or DC 220, 24V, etc. It analyzes electrical engineering equipment and line information for various environmental protections such as short circuits, overloads, and voltage losses. It mainly consists of protection and management components such as fuses, thermal relays, voltage loss coils, rectification system components, and voltage stabilization circuit components.

(3) Signal control circuit. A circuit that can promptly reflect or display data information on normal and abnormal working and living conditions of technical equipment and circuits, such as signal lights of different colors, sound system equipment with different sounds, etc.

(4) Automatic and manual circuits. In order to improve the efficiency of electrical equipment, automatic connections are usually used. However, during installation, debugging, and emergency situations, manual connections need to be set up in the control circuit to switch between automatic and manual modes through switches or combinations of switches.

(5) Brake stop circuit. Cut off the power supply of the circuit, take braking measures such as energy consumption braking, power reverse braking, reverse braking, regenerative braking, etc., to quickly stop the motor.

(6) Self locking and locking circuits. After the start button is released, the circuit remains energized, and the electrical component that can continue to work is called a self-locking component, such as the moving contact of a contactor connected in series in a coil circuit. Two or more electrical devices and components, in order to ensure the safe and reliable operation of the equipment, can only have one that can be started with electricity and the other that cannot be started with electricity, which is called a locking link. For example, the dynamic breaking contacts of two contactors are connected in series in opposite coil circuits.