In every Electrical Machine panel, there are two circuits. One is ‘Power Circuit’ and another is ‘Control Circuit’.
Control circuit as name implies used to control the Power circuit. Control circuit generally operates at low voltage or equal to the level of voltage of power Circuit.
While power circuit operates at high voltage & high current comparatively.
Both power circuit & control circuit works together parallelly. There are multiple components which are used to interlink control circuit & power circuit.
‘Contactor‘ is one of the component in Electrical system which controls the power circuit through control circuit.
This post is all about the contactors. Further in this post, Contactor’s configuration, working & Technical specifications are been discussed.
CONTACTORS
Contactor is an electromechanical device which contains NO-NC contacts, silicon steel stamping & electromagnetic coil. Contactor switches its NO-NC contacts depending upon whether contactor’s coil is energized or not !
(Left)MI50 contactor by L&T | (Right) Contactor TeSys LC1D25 by Schneider Electric
CONFIGURATION & WORKING OF CONTACTOR
Contactor generally contains an Electromagnetic coil, NO-NC contacts, Terminal Screws, Silicon steel stamping & Mechanical Spring mechanism.
Generally, An Electromagnetic coil with silicon steel stamping is placed at last at the bottom of the contactor. NO-NC contacts with silicon steel stamping are placed at the top & mechanical spring is sandwiched between both of them.
A GIF below shows the working of contactor !
An GIF shows working mechanism of contactor
( “For better understanding; ML-1.5 contactor made by L&T is going to be discussed next. This contactor is very easy to understand because every single working component is clearly visible!”)
ML-1.5 contactor by L&T
Assembly of ML-1.5 Contactor by L&T
The NO-NC contacts are fixed with silicon steel stamping & placed at top of the contactor.
These NO-NC contacts are pushed upward by the mechanical spring at normal state when electromagnetic coil is not energized. At that time; NO-NC contacts are present at their normal initial state.
When contactor’s coil get energized; It becomes Electromagnet & attracts silicon steel stamping in along with NO-NC contacts towards downward. Contacts gets pulled down & mechanical spring get compressed which results state of contacts get changed.
Again, When contactor’s coil get de-energized; mechanical spring pushes the contacts upward.
Both the states energized & de-energized are explained in a collage below :
Arrangement of contacts; Depending upon the state of the coil whether coil is Energized or not| ML1.5 By L&T
CONTACTOR’S CONTACTS
There are two types of contacts in contactor; Main contacts & Auxiliary contacts.
Main contacts are heavy contacts through which heavy load current flows. These contacts are basically used for power circuit. Basically power contacts are available in normally NO type. In an image below contacts L1-T1, L2-T2, L3-T3 are shown. These are Main NO contacts through which load current flows, These contacts belong to power circuit.
Main Contacts are L1-T1, L2-T2, L3-T3 | All are NO contacts| Terminals L1 connects to T1, L2 connects to T2 & L3 connects to T3 ML1.5 Contactor By L&T
Auxiliary contacts are low current rating contacts through which minimal control current flows. These contacts are used in control circuit. These contacts can be NO or NC.
These Auxiliary contacts are also available in add-on blocks Which can be connected externally.
ML-1.5 contactor is equipped with 2NO+2NC Auxiliary contacts.
These auxiliary contacts are also connected to same silicon steel stamping through which main contacts are connected. That’s why these all behave in a same manner as power contacts do.
Auxiliary Contacts 2NO+2NC | ML-1.5 Contactor by L&T
Auxiliary contacts position also depend whether coil is Energized or NOT| ML1.5 Contactor By L&T
MORE ABOUT CONTACTORS
Both the contacts whether it is main contact or Auxiliary contacts are fitted with spring mechanism So that contact become firm & No sparking takes place.
Contactor’s electromagnetic coil are available in both the supplies AC & DC with variable voltage ranges. The coil voltage is selected as per according to the requirement.
Some contactors contains auxiliary contacts on their own as like wise in ML-1.5 Contactor While some contactors are without auxiliary contacts While some contactors have provision to add auxiliary contacts through Add-ONN Block.
Contact strips ML-1.5 Contactor By L&T
Main & Auxiliary, Both contacts contain springs| ML1.5 By L&T
For better understanding, ML1.5 Contactor by L&T is discussed next.
Technical Specifications of ML- contactor by L&T
Main Contacts
No. of Poles- 3 Poles
Rates current at 3phase 415Volts- 25Amps
Insulation Voltage- 500 Volts
Rated Impulse Voltage withstand- 8kV
Max. Frequency of operation(Operation/hour)- 750
Service Temperature range- (-20°C to 55°C)
Main terminal capacity( in mm²)- (2×10mm)
Auxiliary Contacts
No. of Built-in Auxiliary Contacts- 2NO+2NC
Rated Current- 4 Amps
Terminal capacity(in mm²)- (2× 2.5mm)
Coil
Coil Voltage at 50Hz(AC) – 110,230,380,440
Coil’s power rating (VA)- 15
Coil pf- 0.8
Typical closing delay- (5-35 msec.)
Typical opening delay- (5-20 msec.)
SUMMARY
There are two circuits in Electrical; One is power circuit & another one is control circuit.
Contactor is the key component which is used to control the power circuit through control circuit.
Contactor is a type of electromechanical element which is equipped with contacts, Silicon steel stamping, springs & electro-magnetic coil.
Contactor changes the state of contact as per according to the state whether electromagnet is energized or not.
Contactor further contains two types of contacts; power contacts & control contacts.
Power contacts are made for power circuit for heavy load current while control contacts are made for control circuit for light current flow.
There are multiple types of contactors, One which contains only power contacts, One which contains the both power & Control, One which contains power contact but it has provision to connect external ad on control blocks.
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