protection and relay scheme

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protection and relay scheme

  1. 1. Protection and Relay Schemes <ul><li> Chris Fraser </li></ul><ul><li>Amanda Chen Wang </li></ul><ul><li>Group#4 </li></ul><ul><li>October 5, 2005 </li></ul>
  2. 2. Agenda <ul><li>Introduction of Protective Relays </li></ul><ul><li>Electrical System Protection with Protective Relays </li></ul><ul><li>Conclusion </li></ul>
  3. 3. What are Relays? <ul><li>Relays are electrical switches that open or close another circuit under certain conditions. </li></ul>
  4. 4. Relay Purpose <ul><li>Isolate controlling circuit from controlled circuit. </li></ul><ul><li>Control high voltage system with low voltage. </li></ul><ul><li>Control high current system with low current. </li></ul><ul><li>Logic Functions </li></ul>
  5. 5. Relay Types <ul><li>Electromagnetic Relays (EMRs) </li></ul><ul><ul><li>EMRs consist of an input coil that's wound to accept a particular voltage signal, plus a set of one or more contacts that rely on an armature (or lever) activated by the energized coil to open or close an electrical circuit. </li></ul></ul><ul><li>Solid-state Relays (SSRs) </li></ul><ul><ul><li>SSRs use semiconductor output instead of mechanical contacts to switch the circuit. The output device is optically-coupled to an LED light source inside the relay. The relay is turned on by energizing this LED, usually with low-voltage DC power. </li></ul></ul><ul><li>Microprocessor Based Relays </li></ul><ul><ul><li>Use microprocessor for switching mechanism. Commonly used in power system monitoring and protection. </li></ul></ul>
  6. 6. How a Relay Works
  7. 7. Sold-State Relay
  8. 8. Advantages/Disadvantages <ul><li>Electromagnetic Relays (EMRs) </li></ul><ul><ul><li>Simplicity </li></ul></ul><ul><ul><li>Not expensive </li></ul></ul><ul><ul><li>Mechanical Wear </li></ul></ul><ul><li>Solid-state Relays (SSRs) </li></ul><ul><ul><li>No Mechanical movements </li></ul></ul><ul><ul><li>Faster than EMR </li></ul></ul><ul><ul><li>No sparking between contacts </li></ul></ul><ul><li>Microprocessor-based Relay </li></ul><ul><ul><li>Much higher precision and more reliable and durable. </li></ul></ul><ul><ul><li>Improve the reliability and power quality of electrical power systems before, during and after faults occur. </li></ul></ul><ul><ul><li>Capable of both digital and analog I/O. </li></ul></ul><ul><ul><li>Higher cost </li></ul></ul>
  9. 9. Why A System Needs Protection? <ul><li>There is no ‘fault free’ system. </li></ul><ul><li>It is neither practical nor economical to build a ‘fault free’ system. </li></ul><ul><li>Electrical system shall tolerate certain degree of faults. </li></ul><ul><li>Usually faults are caused by breakdown of insulation due to various reasons: system aging, lighting, etc. </li></ul>
  10. 10. Electrical Faults <ul><li>majority are phase-to-ground faults </li></ul><ul><li>phase-to-phase </li></ul><ul><li>phase-phase-phase </li></ul><ul><li>double-phase-to-ground </li></ul>
  11. 11. Advantages for Using Protective Relays <ul><li>Detect system failures when they occur and isolate the faulted section from the remaining of the system. </li></ul><ul><li>Mitigating the effects of failures after they occur. Minimize risk of fire, danger to personal and other high voltage systems. </li></ul>
  12. 12. Protective Devices Comparison Relays Circuit Breakers Fuses <ul><li>Acquisition </li></ul><ul><li>Detection </li></ul><ul><li>Activation </li></ul><ul><li>Actuation </li></ul>
  13. 13. Protective Devices Comparison <ul><li>Circuit Breakers V.S. Relays </li></ul><ul><li>Relays are like human brain; circuit breakers are like human muscle. </li></ul><ul><li>Relays ‘make decisions’ based on settings. </li></ul><ul><li>Relays send signals to circuit breakers. Based the sending signals circuit breakers will open/close. </li></ul>
  14. 14. Protective Devices Comparison <ul><li>Fuses V.S. Relays </li></ul><ul><li>Relays have different settings and can be set based on protection requirements. </li></ul><ul><li>Relays can be reset. </li></ul><ul><li>Fuses only have one specific characteristic for a individual type. </li></ul><ul><li>Fuses cannot be reset but replaced if they blow. </li></ul>
  15. 15. Protection and Relay Schemes <ul><li>Motor Protection </li></ul><ul><li>Transformer Protection </li></ul><ul><li>Generator Protection </li></ul>
  16. 16. Motor Protection <ul><li>Timed Overload </li></ul><ul><li>Locked Rotor </li></ul><ul><li>Single Phase and Phase Unbalance </li></ul><ul><li>Other </li></ul>
  17. 17. Motor Protection Timed Overload <ul><li>Solution: </li></ul><ul><li>Thermal overload relays </li></ul><ul><li>Plunger-type relays </li></ul><ul><li>Induction-type relays </li></ul>
  18. 18. Motor Protection Timed Overload Protection <ul><li>Timed Overload Definition: </li></ul><ul><li>Continuously operate motor above its </li></ul><ul><li>rated value will cause thermal damage to </li></ul><ul><li>the motor. </li></ul>
  19. 19. Thermal Overload Relays <ul><li>Use bimetallic strips to open/close relay contacts when temperature exceeds/drops to certain level. </li></ul><ul><li>Require certain reaction time </li></ul><ul><li>Inverse time/current relationship </li></ul>
  20. 20. Thermal Overload Relays
  21. 21. Plunger-type Relays <ul><li>Fast reaction time </li></ul><ul><li>Use timer for time delay </li></ul><ul><ul><li>Such as oil dash pot. </li></ul></ul><ul><li>Inverse time/current relationship </li></ul>
  22. 22. Plunger-Type Relays
  23. 23. Induction-type Relays <ul><li>Most frequently used when AC power presents </li></ul><ul><li>Change taps to adjust time delay </li></ul>
  24. 24. Induction-Type Relays
  25. 25. Motor Protection Stalling <ul><li>Some Definitions… </li></ul><ul><li>Motor Stalling: </li></ul><ul><ul><li>It happens when motor circuits are energized, but motor rotor is not rotating. It is also called locked rotor. </li></ul></ul><ul><ul><li>Effects: this will result in excessive currents flow given the same load. This will cause thermal damage to the motor winding and insulation. </li></ul></ul>
  26. 26. Motor Protection Stalling <ul><li>Similar types of relays that are used for motor timed overload protection could be used for motor stalling protection. </li></ul>
  27. 27. Motor Protection Single Phase and Phase Unbalance <ul><li>Some definitions… </li></ul><ul><li>Single Phase: </li></ul><ul><ul><li>three-phase motors are subject to loss of one of the three phases from the power distribution system. </li></ul></ul>
  28. 28. Motor Protection Single Phase and Phase Unbalance <ul><li>Some definitions… </li></ul><ul><li>Phase Unbalance: </li></ul><ul><ul><li>In a balanced system the three line-neutral voltages are equal in magnitude and are 120 degrees out of phase with each other. Otherwise, the system is unbalanced. </li></ul></ul>
  29. 29. Motor Protection Single Phase and Phase Unbalance <ul><li>These conditions will cause </li></ul><ul><ul><li>Motor winding overheating </li></ul></ul><ul><ul><li>Excessive vibrations </li></ul></ul><ul><ul><li>Cause motor insulation/winding/bearing damage </li></ul></ul>
  30. 30. Motor Protection Single Phase and Phase Unbalance <ul><li>These conditions will cause </li></ul><ul><ul><li>Motor winding overheating </li></ul></ul><ul><ul><li>Excessive vibrations </li></ul></ul><ul><ul><li>Cause motor insulation/winding/bearing damage </li></ul></ul>
  31. 31. Motor Protection Single Phase and Phase Unbalance
  32. 32. Motor Protection Other <ul><li>Instantaneous Overcurrent </li></ul><ul><ul><li>Differential Relays </li></ul></ul><ul><li>Undervoltage </li></ul><ul><ul><li>Electromagnetic Relays </li></ul></ul><ul><li>Ground Fault </li></ul><ul><ul><li>Differential Relays </li></ul></ul>
  33. 33. Transformer Protection <ul><li>Gas and Temperature Monitoring </li></ul><ul><li>Differential and Ground Fault Protection </li></ul>
  34. 34. Transformer Protection <ul><li>Gas Monitoring Relays: </li></ul><ul><li>These relays will sense any amount of gas inside the transformer. A tiny little amount of gas will cause transformer explosion. </li></ul><ul><li>Temperature Monitoring Relays: </li></ul><ul><li>These relays are used to monitor the winding temperature of the transformer and prevent overheating. </li></ul>
  35. 35. Transformer Protection Ground Fault <ul><li>For a wye connection, ground fault can be detected from the grounded neutral wire. </li></ul>
  36. 36. Transformer Protection Ground Fault and Differential Relay
  37. 37. Generator Protection <ul><li>Differential and Ground Fault Protection </li></ul><ul><li>Phase Unbalance </li></ul>
  38. 38. Generator Protection Differential and Ground Fault
  39. 39. Generator Protection Phase Unbalance <ul><li>Some Definitions.. </li></ul><ul><li>Negative Sequence </li></ul><ul><ul><li>Voltage example: </li></ul></ul>
  40. 40. Generator Protection Phase Unbalance <ul><li>Some Definitions.. </li></ul><ul><li>Negative Sequence: </li></ul><ul><ul><li>The direction of rotation of a negative sequence is opposite to what is obtained when the positive sequence are applied. </li></ul></ul><ul><ul><li>Negative sequence unbalance factor: </li></ul></ul><ul><ul><ul><li>Factor= V-/V+ or I-/I+ </li></ul></ul></ul>
  41. 41. Generator Protection Phase Unbalance <ul><li>Negative Sequence Relay will constantly measure and compare the magnitude and direction of the current. </li></ul>
  42. 42. Conclusion <ul><li>Relays control output circuits of a much higher power. </li></ul><ul><li>Safety is increased </li></ul><ul><li>Protective relays are essential for keeping faults in the system isolated and keep equipment from being damaged. </li></ul>
  43. 43. Reference: <ul><li>IEEE Red Book </li></ul><ul><li>Ontario Power Generation Training Course (Electrical Equipment) </li></ul><ul><li>www.howstuffworks.com </li></ul>

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