Electromagnetic contactors are electrical devices for frequent switching of electrical power networks with current, without exceeding the overload threshold. Closing, opening and short-term connection of contacts is carried out by an electromagnetic drive.
Content
- Design of electromagnetic contactors
- The principle of operation of devices
- Operating voltage of the device
- Terms of Use
- Marking and types of structures
- Engine management
- Self-connection
Design of electromagnetic contactors
The main contacts connect and open the power network. They must be designed for continuous rated current and for a large number of connections and disconnections at a higher frequency. The contact position is considered normal if the coil of the device and the large latches are released. Key contacts can be made in the form of a bridge. Lever contacts mean a rotary movable system, bridge contacts are rectilinear.
Arc chambers of continuous current devices are created on the principle of electric arc extinguishing, transverse field in chambers with slotted slots. The magnetic field in the content of most structures is caused by a methodical arc coil.
The contactor consists of the following key parts:
- main contacts;
- arc system;
- electromagnetic construction;
- additional contacts.
The arc-stopping system guarantees the weakening of the electric arc, appears when the key contacts are opened. Arch damping methods and installation of arc crossing systems are formed according to the type of circuit current and the operating mode of the contactor.
The electromagnetic part of the device guarantees its control at a distance in such a case of connection and disconnection. The structure of the system is determined by the type of flow and the control scheme and its kinematic scheme.
The electromagnetic part consists of the following parts:
- core:
- anchors;
- coils;
- fasteners.
The electromagnetic system of a contactor can be calculated to close the valve and keep it closed, or just to connect the valve by keeping it closed. The contactor is turned off after the coils are de-energized under the action of the opening springs or its own weight of the system, but more often the spring.
Auxiliary contacts make transfers in the control circuit and in the blocking circuit. They are designed for a three-dimensional current, the reference current is not more than 20 A, and the current value is not more than 5 A. Contacts are provided both at closing and at breaking in most cases.
AC contactors are manufactured with arc chambers from the mains. Electrical circuits consisting of multifunctional conductive components (control coils, key and additional contacts), in the bulk of cases have the usual form and differ only in the number and type of contacts and coils.
The principle of operation of devices
The contactor is inserted if voltage is applied to the coil of the electromagnetic drive. The armature of the electromagnet is attracted to the core. At the same time, with the anchor, the pendant contact is attracted to the stationary part, and the power circuit encompasses it.
The contactor switches off if the voltage is removed from the solenoid coil. Moving contacts fall away from the moving parts, and the force of the disconnecting (return) spring, which is immobile under the influence of gravity, falls.
Number of key contacts:
- for continuous current contactors 1−2;
- for AC contactors 2-5.
Rated circuit current:
- rated voltage of the main network up to 660 V;
- The rated voltage of the control circuit is 12V, 24V, 48V, 110V, 220V.
Operating voltage of the device
An important parameter is the rated operating voltage. The rated current at the contactor is electricity. The microcontactor is capable of carrying this current with three hidden main contacts; the temperature prevalence of its different parts should not be higher than possible values. In the order of a short working day, the concept of a possible equivalent long current is often used.
Important features of the device:
- The durability of the switching is the ability of the machine to carry a given amount of switching in the presence of current in the circuit and to be suitable for further operation. Up to 2 million cycles.
- Mechanical reliability is the ability of a machine to carry a fixed amount of switching without current in the circuit and to be serviceable. For contactors 10-20 million cycles.
- Switching fluctuations per hour for different series of contactors are 150, 300, 600, 1200, 3600 cycles per hour.
- Own time - the period from the specified time until the contacts are completely covered.
- Voltage and electricity of auxiliary contacts.
- The number of additional contacts and their appearance (disconnection, closing).
The main voltage of the contactor is the high total force for which the contactor is configured. If the rated current and forces of the contactor establish the permissible operating conditions for it in continuous operation, then these operating conditions are formed by the rated operating current and operating force.
Likewise, the operating current, which determines the use of the contactor in the circumstances specified by the manufacturer, is generated depending on the nominal labor force, work order, application category, type of performance and operating conditions. The nominal voltage is equal to the line voltage at which the microcontact can operate under these conditions.
Contactors must be used in accordance with the following parameters:
- by purpose and size;
- according to the category of orders;
- in terms of machine wear resistance and elasticity;
- by the number and implementation of key and additional contacts;
- depending on the type of current and the magnitude of the rated strength and current of the circuit;
- in terms of the rated force and energy consumption of the coils;
- in accordance with the operating mode;
- by climatic characteristics and category of housing.
Terms of Use
In contact with the heater and other devices (for example, in ventilation modes), the microcontactor of the module is used. They have become in demand for the installation of panels on the living space and various automation systems. For example, for lighting control, borehole pump, mechanical redundancy, etc. The microcontactor is ideal for modular devices and does not interfere with the service of the devices in any way.
It should be remembered that the mains voltage should not be higher than 380 volts at a frequency of 50 Hz. But the microcontactor can operate at high power. There are also a number of positive aspects of this device. For example, the almost absolute absence of hum and pulsation, which is very positive if it is used not only in a home shield, but also in public places (hospital, educational institution, etc.). ).
Several labels can be found in the device itself, which, in turn, shows the nominal current, the number of contacts and their type. Currently, you can choose the required device from 25 modifications. In this case, you should pay attention to all indicators, because the rated current of the contacts and the rated voltage must correspond to the dimensions.
Marking and types of structures
There are several common indicators. They help distinguish markings on the surface of the device. Besides, the stamp is indicated by the certificate and passport of the device.
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KT and KTP are crane contactors for direct and alternating current. They have high wear resistance - they are repeated up to several cycles. The current frequency should not be higher than 50 hertz, voltage - up to 380 volts; - KMIs are small triggers that are used to control the operation of motors such as AIR, etc. They operate on a network where the current usually does not exceed 9-95A. The main feature is the installation of switches in hostile areas with high levels of humidity. Their analogue is the KHTE 400A EKF devices, but the permissible current reaches 400 A;
- The function of the IEC and ABB KTI switches is similar to the CMR, except that they control the operation of three-phase motors. In other words, they have a wide range of actions. They switch loads (it takes about 2 seconds to change the mode). Works up to 660 volts;
- KNE is used in existing networks, it can be marine and tropical. Can be mounted on ships;
- The PM and PML are 2 ampere home starters. Lighting is very common in alarm systems. Their counterparts are electropneumatic switching devices;
- Thyristors - devices of the TKPM-121, KTP-121, KKD-121 series. Designed for switching crane mechanisms. They operate at voltages up to 550 volts and up to 50 Hz;
- Starters such as CPV and KTPV have a magnetic arc method, which is an advantage over other types. It is actively used for traction, electric vehicles and other mechanisms.
Engine management
The operation of the machine largely depends on the scope of its application. To control a three-phase motor, the following model of switching on an electromagnetic contactor is used.
When the start button is pressed, the coil begins to acquire an electric current, which forms a magnetic field. In this regard, key contacts are involved, they are hidden. Therefore, after using the "Stop" key, the movement of the rotated particles stops - the contacts are open, the engine stops. It is necessary to pay attention to the fact that after the end the terminal is not fixed, which often causes the starters to break. In this case, it is necessary to repair the switching device itself.
If you need to buy an MK electromagnetic contactor to block individual equipment, then the presented model will do. In the illustration, the start console plays an important role, which after the completion of the starter fixes the key contacts, does not allow them to be connected for a long time. This option is more reliable than the basic one.
The sale of electromagnetic contactors is carried out in special shopping centers for electrical equipment, while the cost depends on the class of the starter. For example, the cost of a conventional CT scan at 10 A varies from 300 rubles.
Self-connection
When you turn on the contactor, you need to determine the mechanism that it will turn on. This can be a motor, pump, fan, heating elements, compressors, etc. The main characteristic of the contactor, which distinguishes it from the machine, is the absence of any protection. Therefore, taking into account the circuits for switching on electrical equipment through a microcontact, it is necessary to take into account the current limiting and heating components.
Fuses and automatics are reused to limit and shut down equipment in the event of short circuits and excessive overloads. Thermal relays are used from the long-term insignificant excess of the rated currents of the working equipment.
In order to correctly connect the contactor to the circuit, it is necessary to clearly understand which of the contacts are power sources, and which are auxiliary, that is, they block the contacts. You also need to look at the value of the switching coil. It should indicate the voltage of its type and magnitude and, in addition, the currents passing through it for standard operation. The contacts may burn during operation, so they must be constantly monitored and cleaned regularly.
To connect a microcontact via a button, a diagram must be considered. The microcontact is designed to start the load, in this case the motor, from a contactor whose coil is rated for 220 VAC. When choosing a contactor, the importance of power supply must be considered. If an electromagnet is designed for constant voltage, it needs such a source.
When the start button is pressed, the contactor coil will close. The power contacts are closed, giving voltage to the induction motor. In addition, contactor K1 is closed, connected to the stop button. It is called an electrical contact because it supplies current, closes the coil when the button is released. When the solenoid shutter release button is pressed, the power is cut off, the contactor batteries break the circuit, and the motor shuts down.
