What is Electromagnetic Relay?
Relays that work on the principle of electromagnetic attraction are known as electromagnetic relays. The magnet is used to create a magnetic field, making it a particular kind of magnetic switch. The switch is then opened and closed using the magnetic field, and a mechanical action is subsequently carried out.
It functions similarly to a contactor but has a smaller range of amperes than a contactor. It controls the large quantity of load current with relatively little power (24 DC volts or 230 AC volts) (up to 5A). Relays also have contacts for NO and NC. It is typically employed to regulate many circuits using a single relay. Relays come in both AC and DC (Direct Current) types. Magnetic relays come in 5, 8, and 14 pin configurations.
Construction of Electromagnetic Relay:
Relays typically consist of three components:
- Electromagnetic coil,
- A Movable Armature and
- Contacts- Normally Open (NO) and Normally Closed (NC)
An electromagnetic coil is created by winding a copper coil or wire in the form of a helix or a circle. When the electromagnetic coil’s terminals get the supply, quickly passes through the copper wires, it begins to produce a magnetic field. Because the magnet is created when the electric current passes through the coil, these electromagnets are momentary magnets.
There are two different kinds of contacts in an electromagnetic relay. Normal open and normal closed contacts make up the two connections.
Normally when the coil is activated, open contacts are creating contacts.
When the coil is not energized, normally closed contacts are forming connections. The common link between normally open and normally closed contacts is known as the movable armature. When the coil is not electrified, it makes contact with the Normally Closed point, and when the coil is energised, it makes contact with the Normally Open contacts.
Working of Electromagnetic Relay:
On the basis of the electromagnet, electromagnetic relays function. The Electromagnetic Relay has two operating conditions:
- One is the Normally Open condition, and
- The other is the Normally Closed condition.
Normally Open Condition:
The contacts are open in a normal situation. The electromagnetic coil is not energised in this condition. When the supply gets to the electromagnetic coil, it begins to generate a magnetic field. The movable armature is drawn to the coil by this magnetic field. In this manner, the circuit closes when the common contact comes into contact with the normally open contact. In this manner, supply travels from the common terminal to the typically open contact.
Normally Closed Condition:
The contacts are closed in this condition. The electromagnetic coil is not now energised, and when it becomes energised, the contact opens, breaking the circuit and preventing the supply flow. The movable armature touches the upper contact when the contact is closed normally.
The external circuit connected between terminals 1 and 2 is currently open, while any external circuit connected between terminals 1 and 3 is currently in a closed position.
The armature is drawn toward the coil when the voltage is applied to it, energising the relay and creating a magnetic field surrounding it. Any external circuit connected between terminals 1 and 2 is now complete. Contact 4 breaks with terminal 3 but makes with terminal 2. The relay remains in position as long as the coil is still electrified.
The moveable armature is connected to terminal 1, and terminals 2 and 3 are the permanent contacts (in some relays the armature remains isolated from all contacts). The basic relay’s contacts function as single pole double throw (SPDT) switches. Relay contacts are remotely controlled, even if switch contacts are manually operated.
What is Relay Contact?
Relay contacts are constructed from low resistance metals and alloys to avoid overheating. Additionally, the metal used to make the contacts must be able to withstand both the welding process that takes place when the contacts close and the arcing that develops when the contacts open.
The contacts shapes should be such that they can withstand the pity effect.
- Palladium, and
- Certain Alloys
are metals that are utilised to make relay contacts. For DC voltages compared to AC voltages, the current at which any particular pair of contacts would interrupt successfully without arcing is often smaller, and it gets smaller at increasing voltages.
Function of AC Relay:
AC relays have a shade coil over a piece of the pole face at the air gap to lessen vibration and chattering of the contacts. The phase of the flux in the shaded area of the pole face is altered by the shading coil. As a result, the flux’s overall force (as measured across the entire pole) is kept from ever reaching zero during the cycle.
Consequently, chattering is reduced to a minimum. A capacitor may be coupled in series with the relay coil in some AC relays to create a device that is sensitive to frequency. The applied AC signal must then be at or close to the coil-capacitor combination’s resonance frequency in order for the relay to be activated.
Advantages Of Electromagnetic Relay:
- Electromagnetic relays are quick to operate and reset.
- Slow operation and reset are both potential outcomes.
- They can be applied to both AC and DC systems to protect ac and dc equipment.
- Simple, sturdy, small, and most trustworthy are just a few of their qualities.
- Additionally, it is feasible to use electromagnetic relays with millisecond-level working speeds.
- These relays are virtually instantaneous. Despite being instantaneous, the operating time of the relay changes depending on the current. with additional arrangements like a dashpot, copper rings, etc.
Disadvantages Of Electromagnetic Relay:
- In order to operate electromagnetic relays rather than static relays, high burden level instrument transformers (CTs and PTs) are needed.
- Dust, pollution, and component ageing all have an impact on relay operation, which can result in inaccurate trips.
- The mechanical inertia component of electromagnetic relays sets a speed limit on operation.
- In electromagnetic relays, there is no directional feature.
- Unlike static relays, demands routine maintenance and testing.
Application of Electromagnetic Relay:
- Several AC and DC instruments are protected by electromagnetic relays.
- The protection of various AC and DC equipment from over or under-current and voltage.
- Used as supplementary relays in protective relay schemes’ contact systems.
- Used for differential protection.
SOME USEFUL QUESTIONS:
1. What is chattering in Relay?
Chattering is a phenomenon when a manual switch quickly and repeatedly switches on and off due to contact vibration.
- Counter input and
- Reset input
could result in malfunctioning.Usually,
- An RC circuit and
- A Schmitt trigger buffer
are used in tandem to reduce chattering.
2. What is an electromagnetic relay used for?
2. Industrial assembly lines, and
3. Machine tool control
all frequently use electro-mechanical relays. They are conveniently offered by relay manufacturing businesses. Relays’ ability to regulate a huge amount of output is one of the key factors in their popularity.
3. What are the types of electromagnetic relays?
- Balanced beam type relay,
- Disc-type induction relay,
- Cup-style induction relay,
- Moveable coil relay,
- Attracted Armature type relay,
- Polarized Moving Iron type relay
are the different types of electromagnetic relay based on their working principle.