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# Relay coordination

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Relay Co-ordination

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### Relay coordination

1. 1.  To determine the ratings and settings of fuses, breakers, relay, etc.  To isolate the fault or overloads. Objective
2. 2. RELAY………  An electrical device, typically incorporating an electromagnet, which is activated by a current or signal in one circuit to open or close another circuit.
3. 3. How to work a relay………  Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit.As relay diagrams show, when a relay contact is normally open (NO), there is an open contact and the relay is not energized. When a relay contact is Normally Closed (NC), there is a closed contact and the relay is not energized.
4. 4. Basic Parts of Relay………  Frame: Heavy-duty frame that contains and supports the parts of the relay.  Coil: Wire is wound around a metal core.The coil of wire causes an electromagnetic field.  Armature: A relays moving part.The armature opens and closes the contacts. An attached spring returns the armature to its original position.  Contacts:The conducting part of the switch that makes (closes) or breaks (opens) a circuit.
5. 5. Basic design or operation  A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts. The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de- energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay is closed, and the other set is open.
6. 6. Protection vs. Coordination  Coordination is not an exact science  Comparison between protection and coordination
7. 7. Comparison Coordination: Protection:  Limit the extend and duration of service interruption  Selective fault isolation  Provide alternate circuits  Prevent injury to employees  Minimize damage to components  Quickly isolate the affected portion of the system.  Minimize the magnitude of available short-circuit
8. 8. Fundamental requirements Of a Relay.  Selectivity  Speed  Sensitivity  Reliability  Simplicity  Economy
9. 9. Selectivity: maximum continuity of service with minimum system disconnection. Speed : minimum fault duration and consequent equipment damage. Sensitivity: operate with low value of actuating quantity.
10. 10. Reliability: assurance that the protection will perform correctly. Simplicity: minimum protective equipment and associated circuit to achieve the protection objectives. Economics: maximum protection at minimum total cost
11. 11. RELAY PROTECTION COORDINATION……  Relay Protection Coordination means that downstream devices (breakers/fuses) should activate before upstream devices.This minimizes the portion of the system affected by a fault or other disturbance. At the substation level, feeder breakers should trip before the main breaker. Likewise, downstream panel breakers should trip before the substation feeder supplying the panel.
12. 12. ISO Standardized Relays
13. 13. Classification of Relays Classification can be done by different ways, such as by function, input, performance characteristics an operating be divided into five types:  Protective Relays: Protective relays and fuses operate on the intolerable power system conditions.They are applied to all parts of the power system; i.e. generates, buses, distribution lines and feeds,etc  Regulating Relays: Regulating relays are associated with tap changer of TFs, on governor of generating equipment to control the voltages level with varying load (used during normal conditions).
14. 14. Continue……  Monitoring Relays: Relays of this type are used in energizing or restoring lines to service after an outage and in interconnecting pre-energizing parts of the systems.  Auxiliary Relay: An auxiliary relay is a relay that assists another relay or device in performing an action. There are two categories: contact multiplication and circuit isolation
15. 15. Other relay classification  Protective relays classified by input are known as current, voltage, power, frequency and temperature relays. Those classified by operating principles are electromechanical, solid state …etc.
16. 16. Applications  Detecting and isolating faults on transmission and distribution lines by opening and closing circuit breakers.  Isolating the controlling circuit from the controlled circuit when the two are at different potentials.  In logic functions.  Time delay functions.  Used to control high voltage circuits with the help of low voltage signals.
17. 17. Advantages of Relays  Used as a kind of safety switch to allow a circuit with a small current through to switch on a circuit that will have a larger current flow through it.  Minimize the amount of damage to the system during a fault.  Small control signal controls a larger load current or voltage.  Decreased electrical noise when switching.  Totally silent operation.  Output resistance remains constant regardless of amount of use.
18. 18. Disadvantages  High burden level instrument transformers are required (CTs and PTs of high burden is required for operating the electromagnetic relays compared to static relays)  Requires periodic maintenance and testing unlike static relays  Relay operation can be affected due to ageing of the components and dust, pollution resulting in spurious trips  Operation speed for an electromagnetic relays is limited by the mechanical inertia of the component