Plc and relay system used in ntpc

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Plc and relay system used in ntpc

  1. 1. PLC and Relay System Electronics and Instrumentation Maintenance Department
  2. 2. Relay System What is relay ? How it works ?
  3. 3. How it works ? Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch position
  4. 4. How it works ?
  5. 5. Small relay logic OUTPUT A B 0 0 0 0 0 1 0 1 0 1 1 1 V+ OUTPUT A B
  6. 6. DISADVANTAGES OF RELAY CIRCUTS  Number of hardware will increase with increase of logic complexity  Relay energizing and de-energizing takes time  High failure rate  Slow performance  Bulky design difficult to manage  Difficult troubleshooting
  7. 7. Drawbacks of Relays are overcome by PLC’s.
  8. 8. PLC What is a Programmable Logic Controller (PLC) ? How PLC works ? What is the need of PLC ? Hardware involved with PLC Advantages of PLC
  9. 9. What is Programmable Logic Controller (PLC) ? CPU Inputs Outputs A PROGRAMMABLE LOGIC CONTROLLER is a solid state control system that continuously monitors the status of devices connected as inputs. Based upon a user written program, stored in memory, it controls the status of devices connected as outputs.
  10. 10. PLC with Distributed I/O Getting Complex CPU Inputs Outputs Remote Outputs Inputs
  11. 11. What is a PLC with Distributed Control? Getting Really Complex CPU Inputs CPU Outputs Outputs Inputs Remote Outputs Inputs
  12. 12. INSIDE PLC Communications Port I n p u t Isolation Barrier C i r c u i t s Central Processor Unit (CPU) MEMORY data program Low Voltage AC Power Supply or DC Power Supply O u t p u t C i r c u i t s Isolation Barrier CR High Voltage
  13. 13. How PLC works?  The CPU contains an “Executive” program that tells the PLC how to:  Execute the control Instructions  User’s Program  Communicate with other devices  Other PLCs, Programming devices, I/O devices, etc.  Perform Housekeeping activities  Diagnostics, etc  This program is stored in “nonvolatile” memory  Meaning that the program will not be lost if power is removed
  14. 14. How PLC works START  Four Steps in the PLC Operations  Input Scan  Scan the state of the Inputs  Program Scan  Processes the program logic  Output Scan  Energize/de-energize the outputs  Housekeeping  This step includes communications, Internal Diagnostics, etc. Housekeeping Output Scan  The steps are continually repeated - processed in a loop Input Scan Program Scan
  15. 15. PLC
  16. 16. Need of PLC  To eliminate the high costs associated with inflexible, relay-controlled systems.  To Measure input with high speed.  Fast Control (Command and Regulation).  Robust Protection.  Diagnosis.
  17. 17. Advantages of PLC  Compact in size.  Less wiring (Wiring between devices and relay contacts are done in the PLC program.)  Easy to implement complex logic.  Faster action and controlling.  Easy troubleshooting.  Easy to implement change in logic.
  18. 18. Leading Brands Of PLC  AMERICAN 1. 2. 3. 4. 5. 6. 7. Allen Bradley Gould Modicon Texas Instruments General Electric Westinghouse Cutter Hammer Square D  EUROPEAN 1. Siemens 2. Klockner & Mouller 3. Festo 4. Telemechanique  JAPANESE 1. 2. 3. 4. Toshiba Omron Fanuc Mitsubishi
  19. 19. Thank you

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