Function relay types
- 1. Functional Relay Types CONTENT: Induction Type Directional Power Relay Distance relay Impedance relay Prepared By Mr.K.Jawahar, M.E., Assistant Professor Department of EEE Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 2. Functional Relay Types • Most of the relays in service on power system today operate on the principle of electromagnetic attraction or electromagnetic induction. • For example, a relay which recognizes over current in a circuit (i.e. current greater than that which can be tolerated) and initiates corrective measures would be termed as an over current relay irrespective of the relay design. • Similarly an overvoltage relay is one which recognizes over- voltage in a circuit and initiates the corrective measures. Although there are several types of special function relays, only the following important types will be discussed in this chapter . Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 3. (i) Induction type over current relays (ii) Induction type reverse power relays (iii) Distance relays (iv) Differential relays Induction Type Over current Relay (non-directional) • This type of relay works on the induction principle and initiates corrective measures when current in the circuit exceeds the predetermined value. Constructionaldetails • It consists of a metallic (aluminium) disc which is free to rotate in between the poles of two electromagnets. • The upper electromagnet has a primary and a secondary winding. The primary is connected to the secondary of a C.T. in the line to be protected and is tapped at intervals. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 4. Operation: • The driving torque on the aluminium disc is set up due to the induction principle. This torque is opposed by the restraining torque provided by the spring. • Under normal operating conditions, restraining torque is greater than the driving torque produced by the relay coil current.Therefore, the aluminium disc remains stationary. • If the current in the protected circuit exceeds the pre-set value, the driving torque becomes greater than the restraining torque. • Consequently, the disc rotates and the moving contact bridges the fixed contacts when the disc has rotated through a pre-set angle. • The trip circuit operates the circuit breaker which isolates the faulty section. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
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- 6. Induction Type Directional Power Relay • This type of relay operates when power in the circuit flows in a specific direction. Constructional details • It consists of an aluminum disc which is free to rotate in between the poles of two electromagnets. • The upper electromagnet carries a winding (called potential coil) on the central limb which is connected through a potential transformer (P.T.) to the circuit voltage source. • The lower electromagnet has a separate winding (called current coil) connected to the secondary of C.T. in the line to be protected. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 7. Operation When the power in the circuit flows in the normal direction, the driving torque and the restraining torque (due to spring) help each other to turn away the moving contact from the fixed contacts. Consequently, the relay remains inoperative. However, the reversal of current in the circuit reverses the direction of driving torque on the disc. When the reversed driving torque is large enough, the disc rotates in the reverse direction and the moving contact closes the trip circuit. This causes the operation of the circuit breaker which disconnects the faulty section. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
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- 9. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 10. Distance relay • Distance relay is non-unit type protection. It is high speed protection and is simple to apply. • Distance protection is a widely used protective scheme for the protection of high and extra high voltage transmission line. • It can be used in carrier aided distance schemes and in auto reclosing schemes. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 11. Types of distance relays • Depend on the ratio of V and I there are five types of distance relays. (i) Impedance relay (ii) Reactance relay (iii) Admittance relay(mho) (iv) Ohm relay (v) Offset mho relay Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 12. Impedance relay • In an impedance relay, the torque produced by a current element is opposed by the torque produced by a voltage element. • The relay will operate when the ratio V/I is less than a pre- determined value. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 13. Types of impedance relay • A distance or impedance relay is essentially an ohmmeter and operates whenever the impedance of the protected zone falls below a pre-determined value. • There are two types of distance relays in use for the protection of power supply, namely; (i) Definite-distance relay :which operates instantaneously for fault upto a pre-determined distance from the relay. (ii) Time-distance relay in which the time of operation is proportional to the distance of fault from the relay point. A fault nearer to the relay will operate it earlier than a fault farther away from the relay. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 14. Definite – Distance Type Impedance Relay Constructional Details: • It consists of a pivoted beam F and two electromagnets energized respectively by a current and voltage transformer in the protected circuit. • The armatures of the two electromagnets are mechanically coupled to the beam on the opposite sides of the fulcrum. • The beam is provided with a bridging piece for the trip contacts. • The relay is so designed that the torques produced by the two electromagnets are in the opposite direction. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 15. Operation: • Under normal operating conditions, the pull due to the voltage element is greater than that of the current element. Therefore, the relay contacts remain open. • when a fault occurs in the protected zone, the applied voltage to the relay decreases whereas the current increases. The ratio of voltage to current (i.e. impedance) falls below the pre-determined value. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 16. • Therefore pull of the current element will exceed that due to the voltage element and this causes the beam to tilt in a direction to close the trip contacts Time-Distance Impedance Relay • A time-distance impedance relay is one which automatically adjusts its operating time according to the distance of the relay from the fault point. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 17. Kongunadunadu College of Engineering and Technology Depar tment of EEE Functional Relay Types
- 18. Reference: • V.K.MEHTA,ROHIT MEHTA, “Principles of Power System”, S.Chand,2018. • B.Rabindranath and N.Chander, ‘Power System Protection and Switchgear’, New Age International (P) Ltd., First Edition 2011. Functional Relay Types Kongunadunadu College of Engineering and Technology Depar tment of EEE