Contactors are a broad group of electrical devices. In control systems, together with other devices, they are responsible for closing and opening electrical circuits. The contactors are characterized by high strength and mechanical durability. They are capable of multiple switching and carrying high loads occurring in power networks. They are responsible for connecting the main circuits in construction machinery systems and rail vehicle drives.
Contactors have a special place among electrical devices. Due to their capabilities and construction, they are used for many tasks in machine control systems. Due to the structure and parameters, we distinguish several groups of devices, including direct and alternating current power contactors, auxiliary contactors, modular contactors. Power contactors enable control of electric motors, both cage and ring motors, as well as pumps, heaters, resistance furnaces and other heating devices. In high-power supply systems, such as trams and railroads , they turn on and off the power supply to vehicle propulsion engines. The functionality of the contactors allows to minimize the risk of failure and improve the process of controlling devices and lines of industrial automation.
Depending on the type and destination, there are single-phase and three-phase contactors. In AC-powered networks, the energy transfer capacity is usually from 12V to 500V. The operating power of the most popular contactors ranges from a few to several hundred amps. The most common DC powered contactors are 24V and 48V. The operation of the motors is controlled by contactors belonging to one of the user classes AC1 to AC4 for alternating current and DC3 and DC5 for direct currents. Additionally, in industrial and domestic applications, more categories are available for controlling incandescent lamps, transformers and induction devices.
Depending on the system load, a specific user category corresponds to the power of the devices they control. For safety reasons and to increase the service life of associated devices, the principle of mounting a contactor at least twice as large as the currents loading the system in which it works is applied.
The contactors are capable of carrying a wide range of currents. In the power supply systems of industrial devices and vehicle operation control, they support battery tractions by transmitting high power currents. Working contacts are the executive element in all contacts, regardless of their purpose. Their number usually ranges from one to four pairs in the system. Switching the contact position is done by an electromagnet or a solenoid valve. An electromagnetic contactor can have several pairs of working contacts. Their work is usually supported by springs enabling the opening of the contacts. The normal operating state of the relay is when no forces are acting on it. Because of this, we distinguish between two main types of contactors having normally open (NO) and normally closed (NC) contacts.
Due to their application and construction, most contactors are modular. Their design allows for any configuration of the systems in which they work. In combination with additional contacts, they enable maintaining the state of various devices and controlling the operation of motors. Electromagnetic contactors are suitable for independent installation in the control panel of the machine or the vehicle in which they work, as well as for modular devices in control cabinets and housings. As standard, it is possible to mount an electromagnetic contactor on a TH35 mounting rail. The cabling is provided by means of typical screw connectors.
