Get to Know About the Contactors in Detail

A magnetic contactor is a tool or switch that, when needed, uses magnetism to close or open an electric circuit.

Contactor construction

Three components make up a contactor;

• An electromagnet or a coil
• Contacts
• Encloser or Frame

Electric coil or magnet

The coil functions as an electromagnet because it is looped around an electromagnetic core. It typically consists of two parts: a fixed component and a moveable part. The two pieces are joined together by a spring. Consequently, a spring return system exists. The movable component is attached to a rod. An armature is another name for this road. Both contacts are linked when the force of the coil is greater than the force of the spring, and both contacts are withdrawn when the force of the spring is more than the coil force.

To activate the electromagnet's core, a very small amount of current will pass through the spring from the supply or external control circuit. To lessen the eddy current in AC applications, the electromagnetic core is constructed of laminated soft iron. Eddy current is not a problem for DC applications since the core is built of solid steel. The electric contactor is also a useful part.

Embedding or Framing

The contactor's interior components are safeguarded by the enclosure. Plastic, nylon 6, ceramic, or Bakelite are used in its construction. The contacts and magnets are housed by it. The enclosure is used to protect the contacts from weather, dust, oil, and other explosive risks as well as to insulate them from them. When energized, it prevents direct touching or contact.

Contacts 

The whole load current will only flow from this one component. As a result, it is a crucial part of the contactor. Power contact, auxiliary contact, and contact spring are the different types of contacts. Power contacts come in two varieties: stationary contact and moveable contact.

The contacts' substance offers a strong welding resistance and consistent arc resistance. These materials must be resistant to arc, erosion, and mechanical stress. Due to the full load current passing through the contacts, this material has the lowest resistance conceivable. These magnetic contactors are constructed of silver cadmium oxide and silver nickel for low-current applications and silver tin oxide for high-current applications including DC.

NEXT: All about Sine Wave Inverters and their Importance

Working Principle of Thermal Overload Relay

When the temperature rises over a certain threshold, the relay trips. It opens the circuit and disconnects the damaged equipment. For instance, an electric motor may overheat as a result of an overload brought on by any of the following circumstances:

• Excessive load
• High-temperature outside
• Mechanical attachment
• Electricity supply issue

Working Principle of a Thermal Overload Relay

The amount of current flowing through the linked motor or circuit determines how the thermal overload relay operates. It is intended to simulate the heat produced by the appliance using this current to ascertain when an overload may result in damage.

Parts for Thermal Overload Relays

A thermal relay is made up of a variety of pieces, some of which are movable. The following are the primary components of a thermal overload relay that contribute to temperature sensing and the tripping action:

 

• Temperature-sensing component: Usually, this is a bimetallic strip made of two strips of different metals. Depending on how much current is going through the strip or how hot the surroundings are, the strip will expand by a certain amount.
• Tripping mechanism: This is the area of the relay that, when the temperature sensor element detects a sustained overload, trips off using levers and slides. Trip lever, contact lever, trip slide, and springs are some of the components.
• Contacts: When a thermal overload relay is triggered, these component components open and shut to let current passage or interrupt it. The two sets of contacts on a standard thermal relay are generally closed on one set and open on the other. The contacts change positions in response to an overload to stop the current flow.

Operation of a Thermal Overload Relay

Based on the components we just covered, the overload thermal relay operates as follows.

• The bimetal heating coil emits heat when electricity passes through it. A continuous overload might eventually cause the bimetallic strip to expand and bend, depending on the set rating.
• This will exert pressure on the relay's trip lever, opening the usually closed connections while closing the typically open contacts. 
•  The afflicted piece of equipment is decoupled from the power source as a result of the activity.

A tripping indication is set off to signal that the device has been unplugged when this occurs. The tripped relay can then be reset as needed or once the particular issue has been fixed.