[Relay] types of relay\ How does work\like as buchholz relay\Contactor\Latching relay\ Reed relay

Relay/How does work\types of relay 

           What is relay?               

• ·          A relay is a elactro-mechanical device which works on the principle of  magnetic attraction, or magnetic induction.
• ·           A relay can be used as a switching device as well as sensing device in electrical circuit ,arrange to make logical decision.

• ·       The output from this circuit can be used to operate and provide safety to electrical load, such as   motor, heater,tv etc

→Any electrical device having two states.

                    1.Normal state→→→off condition→→NO

2.   Excited state –On condition    →→→        NC

relay inner construction diagram

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dc source for coil=v

Use of relay:
It provide electric isolation .

    Very short time on/off(in milli sec ,micro sec)

     It can generate single pulse.

    It is high reliability .

    It is fault free.

Usually there are two types of relay.

1.    Latching relay-it can have one or two coil and it can remain  last position when the current is turned off. These type of relay useful in application where power consumption must be low because they required no current to maintain their position.

2.    Non-latching relay—it has spring or magnet that maintains initial state of NC(normal close) when no current flowing  through coil .when current flows through the coil then the contact is opened we can say.

Relays are available in different pin configuration like as 3 pins, 4pins,5 pins. The way in which these relays are operated is shown in figure below.Switching contact can be SPST,SPDT,DPST and DPDT types. Some of the relays are  normally open(NO) and the other are normally closed(NC) types.

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dc source for coil=v

         Different Types of relays

1.      Coaxial relay

2.      Contactor

3.      Force-guided contacts relay

4.      Latching relay

5.      Machine tool relay

6.      Mercury relay

7.      Mercury-wetted relay

8.      Multi-voltage relays

9.      Overload protection relay

10.   Polarized relay

11.   Reed relay

12.   Safety relays

13.   Solid-state relay

14.   Static relay

15.   Time delay relay

16.   Vacuum relays

   17. Thermal

·        OT trip (Oil Temperature Trip)

·        WT trip (Winding Temperature Trip)

·        Bearing temp trip etc.                                        

    18. Float type

·        Buchholz

·        OSR

·        PRV

·        Water level Controls etc.

 19.Inverse Definite Minimum Time Relays (IDMT Relays)

20.Differential Relays

Now we will discusses about more usable relay one by one.

1.Coaxial relay

A relay designed for opening or closing a coaxial cable circuit without introducing a mismatch that would cause wave reflections Explanation of coaxial relay.

Contactor

A contactors is an electrically-controlled switch used for switching an electrical power circuit.^[1] A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt AC coil electromagnet controlling a 230-volt motor switch.                  

                         Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors.

Force-guided contacts relay-Force guided relays are guaranteed, that when they do stick, they can never have both a normally open and normally closed condition simultaneously. So, the one stuck contact keeps any other contacts whether normally open or normally closed from changing states. Force guided relays are slower.

 Overload protection relay-it is used to protect conductors or electrical device from excessive current flow. overload relay finds different type like that thermal protection relay,magnetic overload relay etc.

 
Polarized relay

A polarized relay places the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion.


Reed relay(magnetic reed switch)

• The reed relay consists of a switch with magnetic contacts that move under the influence of an external magnetic or the induced field from its solenoid(coil).
•   The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them.  
• The reed relay sealed in a long narrow glass tube ,which have contact protected from corrosion .  

working principle 

i       it's work on the  faraday's law of induction.

       How Does a Reed Switch Work

          The switching mechanism is comprised of two ferromagnetic blades, separated by only      a few microns. When a magnet approaches these blades, the two blades pull toward            one another. Once touching, the blades close the normally open (NO) contacts,                   allowing electricity to flow.

     Applications- reed switches and reed sensors in electronics and communication, robotics and automation, domestic goods, automotive .

solid -state relay(SSR)

• it is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals.
• It can be used to control electrical loads without the use of moving parts.

        if you want to more detail then click now →

static relay

The relay which does not contain any moving parts is known as the static relay. In such type of relays, the output is obtained by the static components like magnetic and electronic circuit etc. The relay which consists static and electromagnetic relay is also called static relay because the static units obtain the response and the electromagnetic relay is only used for switching operation.

Time delay relay-Their purpose is to control an event based on time. The difference between relays and time delay relays is when the output contacts open & close: on a control relay, it happens when voltage is applied and removed from the coil; on time delay relays, the contacts can open or close before or after some time delay.

Thermal relay-A relay that opens or closes contacts with a bending mechanism as a result of the difference in the expansion coefficients of a bi-metal, which is heated by the current. The thermal relay switches a magnetic contactor to protect a motor from overload.example -  OT trip (Oil Temperature Trip),       WT trip (Winding Temperature Trip), Bearing temp trip etc. 

float type relay-

Buchholz-

• it is used for safety purpose of transformer to internal fault.
• which is actuated to gas.
• The Buchholz relay is placed between the main tank and the conservator.  
• his type of relay is used to higher rating of transformer (more than 500 KVA).

what is relay in detail video here ←←https://www.youtube.com/watch?v=RX1VOxLN70s