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Relay Presentation PPT by G@nesh

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A clear description of Relay by a trainee of NTTF-HNTC

Published in: Engineering

Relay Presentation PPT by G@nesh

  1. 1. Presented by : D.Thiru
  2. 2. Relays are a remote control electrical switch that can be switched using low current to control a high current load. Water level Indicator
  3. 3. Relays were invented in 1835 by American electromagnetism pioneer Joseph Henry, in a demonstration at the College of New Jersey. R E L A Y
  4. 4. RELAY  A relay is an electrically operated switch.  Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.  The coil current can be on or off so relay have two switch positions and most have double throw (changeover) switch contacts.
  5. 5. • A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. • The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches.
  6. 6. o The relay’s switch connections are usually labeled COM, NC and NO: oCOM =Common, always connect to this, it is the moving part of a switch. oNC= Normally Closed,COM is connected to this when the relay coil is off. oNO= Normally open,COM is connected to this when the relay coil is on. SYMBOL
  7. 7. Relay operation based on LoadRelay operation based on Load  Load side. (red)  Control side. (green)
  8. 8. Drawn in natural state. Where the voltage present when load side is open. Relay operation (off) When there is current through the coil of wire on the control side a magnetic field is produced. This magnetic field closed the contacts on the load side. Relay operation (on)
  9. 9.  In this relay’s natural state it is in the normally open state.  When the coil is non-energized the contacts are open. Normally open Normally closed  In this relay’s natural state it is in the normally closed state.  When the coil is energized the contacts closed.
  10. 10. • 5(Five) pin relay. • Most common contains normally open and normally open contacts. • 4(Four) pin relay. • Contain either normally open or normally closed.
  11. 11. Typical 5 Pin Relay Pin Identification
  12. 12. Types of Relay switching contacts
  13. 13. Switch ratings (voltage and current) The relay’s switch must be suitable for the circuit they are to control. You will need to check the voltage and current ratings. Note that the voltage rating is usually higher for AC, for example: “5A at 24V DC or 125V AC”.
  14. 14. RELAYS
  15. 15.  Relays can switch AC and DC.  Relays can switch higher voltages.  Relays are often a better choice for switching large currents (>5 A).  Relays can switch many contacts at once.
  16. 16.  The contacts becoming worn, resulting in a limited lifespan.  That they don't perform that well when it comes to switching high inrush currents.
  17. 17.  The Electromagnetic relays are employed for the protection of various AC and DC equipments.  In the over/under current and voltage protection of various AC and DC equipments.  For differential protection.  Used as auxiliary relays in the contact systems of protective relay schemes.
  18. 18. Pls.…

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