There are many kinds of electrical components, and each type of component corresponds to a different function. This article is Inotoday Electronic Technology Co., Ltd., which summarizes the functions of commonly used electrical components. I hope it can be helpful to everyone.

1. Control components


Function: AC contactor is an electrical appliance used to frequently switch on and off the main circuit with load or large-capacity control circuit.

2)Control relay

Function: Intermediate relay, intermediate relay is used as auxiliary control in automatic control, used to transmit signals or control multiple circuits at the same time.

3)Master command, button, indicator light

Function: It is an electrical appliance used in the automatic control system to send control instructions or display status. According to different purposes, it can be divided into: master controller, button, transfer switch, indicator light, buzzer, button with light, etc.

2. Detection components

1)Current transformer

It is used to detect the line current. According to different models, it can be threaded or pierced. The secondary side must be reliably grounded.

2)Ammeter, voltmeter, watt-hour meter and other testing instruments

It is used to detect current (generally with current transformer), voltage, electric energy, etc. Pay attention to the difference between the actual detected value and the displayed value.

Pay attention to the matching of the watt-hour meter with the transformer, as well as the difference between single-phase, three-phase three-wire, and three-phase four-wire.

3)Timers, counters, etc.

Used to measure time and quantity. Pay attention to the number of digits and voltage level required by the user.

3. Driver and PLC system


Function: Control the frequency through rectification and inverter to realize speed regulation. Commonly used frequency converters are AC-DC-AC type.

Commonly used control methods include V/F control, vector control, and direct torque control; the speed regulation methods mainly include: multi-function terminal speed regulation, analog speed regulation, and communication speed regulation.

The overload capacity of the frequency converter is generally approved by overloading for three minutes and 60 seconds, and the overload multiple ranges from 1.36 to 1.6 times; parameters such as rated output current, light overload rated output current, heavy overload rated output current, and overload current should be distinguished.

The following two principles must be grasped when selecting a frequency converter: 1. The rated output current of the frequency converter must meet the rated current of the motor; 2. The overload current of the frequency converter must meet the overload current of the motor.

2)Soft starter

A soft starter (soft starter) is a motor control device that integrates motor soft start, soft stop, light load energy saving and various protection functions.

The soft starter uses three-phase parallel thyristors as voltage regulators, which are connected between the power supply and the motor stator. Such a circuit is a three-phase fully controlled bridge rectifier circuit. When using a soft starter to start the motor, the output voltage of the thyristor gradually increases, and the motor gradually accelerates until the thyristor is fully turned on, and the motor works on the mechanical characteristics of the rated voltage to achieve smooth start, reduce the starting current, and avoid starting overcurrent tripping. When the motor reaches the rated number of revolutions, the starting process is over, and the soft starter automatically replaces the thyristor that has completed the task with a bypass contactor to provide the rated voltage for the normal operation of the motor, so as to reduce the heat loss of the thyristor and prolong the service life of the soft starter , improve its work efficiency, and avoid harmonic pollution to the power grid. The soft starter also provides a soft stop function. The soft stop is the opposite of the soft start process. The voltage is gradually reduced, and the number of revolutions is gradually reduced to zero, so as to avoid the torque impact caused by free stop.

Soft starters are divided into built-in bypass contactors and external bypass contactors, and special attention should be paid to the design.


The so-called multi-drive is a frequency conversion control method that separates the rectification and inverter of the frequency converter and shares the DC bus.

There are several forms of rectification such as diode rectification and IGBT rectification; according to the way of energy consumption, it is generally divided into two types: one is without feedback, and the energy is consumed on the braking resistor through the braking unit; the other is with feedback , to feed back the energy generated by braking to the grid. This is divided into several types such as adjustable DC bus voltage and non-adjustable DC bus voltage.

4)DC drive

Controlling DC motors may be encountered in some special projects or some transformation projects.

There are two basic parameters: armature current and field current. The excitation current is divided into built-in and external, which vary with different manufacturers and specifications. The effect of speed regulation is achieved by controlling the armature current.

Pay attention to the relevant parameters such as the armature and excitation voltage of the motor, select the appropriate driver, and use parallel or series connection to achieve the control effect.

5)Stator voltage regulation driver

The voltage is controlled by controlling the firing angle and on-off of the thyristor (SCR), so as to achieve the purpose of speed regulation. Mostly used in harsh environments.

The resistance of the stator voltage regulation is different from the conventional cutting resistance, so special attention should be paid to the design; generally, the rotor frequency feedback is used to improve the control accuracy; some commutation is carried out through contactors, and some commutation is carried out by controlling the on and off of thyristors.

6)PLC system

The PLC is the control center of the equipment, and the following aspects should be paid attention to during design:

System network: First of all, the system network must be built well, with clear layers. Communication between inverter and PLC, communication between PLC master station and slave station, communication between PLC and upper network (central control room, etc.), communication between PLC and field devices, etc., all need to be adjusted one by one. Make it clear.

Module configuration: A PLC system generally includes the following parts: power supply module, CPU module, digital input and output module, analog input and output module, communication module, backplane or guide rail, extension cable, special module, etc.

4. Others

1)Knife switch, reversing switch

Function: It is used to disconnect the main circuit of the power supply infrequently, forming an obvious breakpoint. Without an arc extinguishing device, it cannot be operated with a large current, and has no protection function; the reversing switch has the function of reversing.

2)Circuit breaker

Function: Used for line protection, the main protections include: short circuit protection, overload protection, etc., and can also be used to cut off the circuit infrequently under normal conditions.


Function: The fuse is the simplest protective device, which mainly plays the role of short-circuit protection in the circuit.

4)Knife fuse switch

Function: Mainly used for short circuit protection of the power circuit, and can also be used for infrequently cutting off the circuit under normal conditions.

5)Overvoltage protector (surge protector)

Function: Used for overvoltage protection of the line, mainly used to protect the impact of induced voltage caused by lightning, etc., and protect the electronic components on the line.

6)Thermal relay

Function: Used for overload protection of the control object (motor), commonly used in the protection of multiple motors.

7)Other protective relays (phase sequence relay, overvoltage, undervoltage relay, overcurrent, undercurrent relay, residual current relay, etc.)

①Phase sequence relay

Function: Used for phase loss and phase error protection of incoming power supply. Some phase sequence relays also have protection functions such as overvoltage and undervoltage.

② Overcurrent relay

Function: It is used to quickly cut off the circuit when the circuit is short-circuited or seriously overloaded. Conventional control circuits are generally protected by overcurrent relays.

③Under current relay

Function: Used for circuit undercurrent protection, mostly used for conventional circuit energy consumption and eddy current undercurrent protection.

④Residual current relay (leakage current relay)

Function: The residual current relay detects the residual current and compares the residual current value with the reference value. When the residual current value exceeds the reference value, it sends out a mechanical switch signal to trip the mechanical switch or the sound and light alarm device sends out an alarm. .


Function: It plays the role of isolation and voltage transformation in the electrical circuit. According to different functions, it can be divided into: lighting transformer, control transformer, energy consumption transformer, eddy current transformer, autotransformer, etc.

The transformer can play a good role in isolation; the secondary side of the transformer should be effectively grounded; the overload capacity of the transformer is generally strong and the efficiency is relatively high.

9)Reactor (incoming line reactor, outgoing line reactor)

Line reactor: reduce the harmonic components (5th, 7th, 11th) generated by voltage spikes caused by the filter capacitor of the frequency converter; the filter inductance added to the line will enhance the anti-interference of the frequency converter.

Outgoing reactor: increase the cable length from the drive to the motor. (due to the increased cable length, the capacitance of the cable to ground cannot be ignored)


Function: Reduce EMC electromagnetic interference. Electromagnetic interference is divided into low frequency and high frequency. It is generally added to the control loop or PLC loop.

It is divided into active filter and passive filter. Passive filter is generally suitable for high power, and active filter is generally suitable for small capacity.


Braking resistor: The resistance and power of the braking resistor need to be calculated and verified; if the braking resistor is too large, it will easily cause overvoltage on the DC bus; if the braking resistor is too small, it will easily cause the braking unit to overheat and burn out the braking unit.

12)Terminal block

Terminal blocks are generally divided into two types, one corresponds to O-type terminal nose, and the other corresponds to needle-type terminal terminal;

Special terminals: double-layer connected terminals, double-layer non-connected terminals, fuse terminals, diode terminals, etc.;

Commonly used terminal accessories: retainer, end plate, marking number, marking seat, bridge piece;

13)Wires and cables

The wire is single-core, and the cable has single-core or multi-core; the structure of the cable generally includes: conductor, insulation, filler, sheath, shielding layer, reinforcing core, etc.

The above is a summary of the functions of electrical components.

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