Contactor is an electrically controlled switch that works like relay. Case of contactor is little different from relay. Unlike relay, contactor uses as high power transmitting switch. It can be use as switch if we want to control high power lines and circuits. Due to its property to be use in high power applications like driving motors rated more than thousands of kilowatts rating and activating/deactivating power distribution lines. A small contactor is easy to hold in hand and its weight is less then 2kg it can be single phase or poly phase it can work with 22KVA to 55KVA rated load however there are very heavy duty contactor with huge size, weight and power rating.
Working of a Contactor:
There are three parts of a contactor
Contacts
Electromagnet
Enclosing Frame
Contacts:
Contacts are current carrying part of contactor. In case of three-phase system there will be 3 contacts in contactor. It includes Power contacts, an auxiliary contact uses some time and contact springs. Springs usually don’t allow power contact to be close however if we push connected frame’s black plastic button it shorten power contacts. Main wires from phase are connected with power contacts. When we push black Plastic button above contactor it short power lines and let the circuit completed. Here electromagnet also force black button downward if we energize it. Auxiliary Contacts Are called NO and NC abbreviation of normally open and normally close. They are switches use in contactor. A normal position of a contactor is position when power contacts are open. It means when black plastic button is pressed it will no longer be in normal state. At normal state NO is open and NC is closed. Similarly when black button pressed NO will close and NC will open. Both work as Q and Q Not. If one is open other is close.
Electromagnet:
This part of contactor is the at the bottom side of contactor. Here a copper coil is located to produce magnetic flux. Its both terminals are called A1 and A2. We connect A1 with phase and A2 with neutral to energize coil. An iron bar place in the coil it is use to attract core that is linked with flux of coil. Over all we energize coil core linked with coil attract downward where iron bar is located and it cause switch on to the main line.
It is just a frame that holds all accessories together as one device. It is made of non conductive material like plastic. Nylon is used in some areas of it for safety from damage due to mechanical movement.
Applications:
In some of old control systems as well as new one contactor uses excessively. It uses to drive heavy duty motors as it is key device for safety. We can perform different logic operation with a combination of contactors. Power supply of a computer works on same principle as contactor (computer doesn’t turn on itself after load shedding) But in case of computer relay will be enough (PC supply is 500watts no need of heavy contactor). It was used with old window air conditioners AC.
