Contactors
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 types
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.
Construction of contactors
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.