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Types of relay


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relay types
relay construction
protection zones

Published in: Engineering
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Types of relay

  2. 2. What is relaying?
  3. 3. Definition of Protective Relay  A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit.
  4. 4. Types of relay  Definite time relays  Differential relay  Solid state relays.  Electromechinical relay  Backup relay  Current relays.  Voltage relays.  Restricted earth fault.  Bus bar protection.  Frequency relays.
  5. 5. The differential relay actually compares between primary current and secondary current of power transformer, if any unbalance found in between primary and secondary currents the relay will detect and trip both the primary and secondary circuit breaker of the transformer. Differential Relay
  6. 6. Solid State Relay SSRs (Solid State Relays) have no movable contacts. which enables high-speed and high-frequency operation. That’s why it provides Solid-state Relay for enormous range of applications.
  7. 7. Electromechanical Relay Electromechanical relay consisit of a spring, moveable armature, electromagnet, moveable contact, & stationary contact. The spring keeps the two contacts separated until the electromagnet is energized, pulling the two contacts together.
  8. 8. Electromechanical Relay
  9. 9. The nature of relaying Reliability, dependability and security  Reliability is generally understood to measure the degree of certainty that a piece of equipment will perform  Dependability is the measure of the certainty that the relays will operate correctly for all the faults for which they are designed to operate.  Security is defined as the measure o f the certainty that the relays will not operate incorrectly for any fault  Loss o f a power system element due to an unnecessary trip is therefore less objectionable than the presence of a sustained fault.  A relay would be considered to be secure if it operates for the faults of its zone
  10. 10. Protection zones
  11. 11.  A relay must: ◦ Operate quickly ◦ Extract significant information from distorted current and voltage waveforms Relay speed
  12. 12. Primary and backup protection The main protection system for a given zone of protection i s called the primary protection system.  It operates in the fastest time possible and removes the least amount of equipment from service.  If primary protection fails duplicate, backup or breaker-failure protection operates and save the system  Backup relays are generally slower than the primary relays and remove more system elements than may be necessary to clear a fault  Breaker failure relays are a subset of local
  13. 13. Single- and three-phase tripping and reclosing  large proportion of faults on a power system are of a temporary nature, the power system can be returned to its pre-fault state if the tripped circuit breakers are reclosed as soon as possible.  Reclosing can be manual or automatic. Some of the common interlocks for reclosing are the following: ◦ Voltage check: Used when good operating practice demands that a certain piece of equipment be energized from a specific side ◦ Synchronizing check: This check may be used when the reclosing operation is likely to energize a piece of equipment from both sides. ◦ Equipment check: This check is to ensure that some piece of equipment is not energized unintentionally.  High speed reclosing is in less than a second and
  14. 14. Elements of a protection system Battery and DC supply  Tripping power, as well as the power required by the relays, sometimes cannot be obtained from the AC system, so it is usually provided by the station battery  Battery is rated to maintain adequate DC power for 8 – 12 hours following a station blackout
  15. 15. Questions