The electrical control system is generally called the secondary control loop of electrical equipment. Different equipments have different control loops, and the control methods of high-voltage electrical equipment and low-voltage electrical equipment are also different.
The main function
In order to ensure the reliability and safety of the primary equipment operation, a number of auxiliary electrical equipments are required to serve, and a combination of several electrical components capable of realizing a certain control function is called a control loop or a secondary loop. These devices have the following features:
(1) Automatic control function. The volume of high-voltage and high-current switching devices is very large. Generally, the operating system is used to control the switching and closing. Especially when the equipment fails, the switch needs to automatically cut off the circuit, and there must be an automatic control device. Automatic control of power supply equipment.
(2) Protection function. Electrical equipment and lines will malfunction during operation. The current (or voltage) will exceed the range and limits of equipment and line operation. This requires a set of detection of these fault signals and automatic adjustment of equipment and lines (disconnect, Switch the protection device, etc.).
(3) Monitoring function. Electricity is invisible to the eye. Whether a device is energized or de-energized cannot be distinguished from the outside. This requires setting various audio-visual signals, such as lighting and sound, to perform electrical monitoring on the primary device.
(4) Measurement function. The lighting and audible signals can only qualitatively indicate the working state of the equipment (with or without power). If you want to know the working condition of the electrical equipment quantitatively, you need various measuring instruments to measure various parameters of the line, such as voltage. , current, frequency and power size.
In the operation and monitoring of equipment, traditional operating components, control appliances, instruments and signals are mostly replaced by computer control systems and electronic components, but there are still some applications in small devices and locally controlled circuits. . This is also the basis for the realization of microcomputer automation control.
System composition
The basic circuit of a commonly used control circuit consists of the following parts.
(1) Power supply circuit. The power supply for the power supply circuit is AC380V and 220V.
(2) Protection circuit. The working power supply of the protection (auxiliary) circuit has single-phase 220, 36V or DC 220, 24V, etc., and various protections for short circuit, overload and voltage loss of electrical equipment and lines, by fuses, thermal relays, and voltage loss coils. It consists of protective components such as rectifier components and voltage regulator components.
(3) Signal loop. A circuit that can reflect or display the normal and abnormal working status information of equipment and lines in time, such as signal lights of different colors, audio equipment with different sounds, etc.
(4) Automatic and manual circuits. In order to improve work efficiency, electrical equipment generally has an automatic link. However, in the process of installation, commissioning and emergency, the manual link is also required in the control circuit, and the automatic and manual conversion is realized by a combination switch or a changeover switch.
(5) Brake parking circuit. Cut off the power supply of the circuit, and take some braking measures to make the motor quickly stop the control links, such as energy braking, reverse power braking, reverse pull braking and regenerative braking.
(6) Self-locking and locking the same way. After the start button is released, the line remains energized, and the electrical part that the electrical equipment can continue to work is called the self-locking link. For example, the moving contact of the contactor is connected in series in the coil circuit. Two or more electrical devices and components, in order to ensure the safety and reliability of the equipment operation, can only be activated by one power-on, and the other protection link that cannot be powered on is called the blocking link. For example, the breaking contacts of the two contactors are respectively connected in series in the counterpart coil circuit.
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