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Discrete Control: Types of Relays

only 3 types were included: for reporting purposes only

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Discrete Control: Types of Relays

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  1. Discrete control Relay/Types of Relays

  2. Objectives: At the end of the discussion, the students to be able to: • Understand the function of relay • Familiarized the different types of relays • Use the relay in hands on activities

  3. Relay • Is an electrical switch that control (switch on & off) a high voltage circuit using a low source voltage • A isolates the low voltage circuit from voltage circuit. relay completely the high

  4. Types of Relays • Differential relays • Distance relays • Frequency relays • Polarized relays • Microprocessor-based relays • Sequence relays • Rotary relays • Moving-coil relays

  5. Differential Relay

  6. Differential protection compares two (or more) currents to locate a fault; which actually makes current protection. In comparison with other types of protection, differential current protection possesses an absolute selectivity in the sense that it operates smartly only in those cases where the fault is within the protected zone and does not operate at all if the fault is out of its zone. • The zone of the differential relay is limited by a part of the electric circuit between the current transformers (CTs), to which the relay is connected. Due to such high selectivity of protection, there is no need to activate a delay for the relay pick-up, which is why all differential relays are high speed. That being so, extraordinarily high selectivity and high speed of operation are the distinguishing features of differential protection. •

  7. Distance Relays

  8. A relay that functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits. If each of the relays installed along the line have time delays depending on impedance (distance), the relay which picks up first will always be the one that is nearest to the point of short-circuiting. This is the main purpose of distance protection. In circuits with a two-way supply, distance protection is directional.

  9. Frequency Relay

  10. The frequency decreases because of power system overload, while a frequency increase is evidence of a power excess. Power excess occurs in the system when one or several hard-loaded lines are suddenly disabled. Surplus power is directed dangerous power flows that can lead to a power system breakdown. That is why it is so important to control voltage frequency. Like all other parameters of electric circuits, frequency is controlled by special relays. to other lines, causing

  11. Polarized Relay A polarized relay is a sort of direct current (DC) electromagnetic relay with an additional source of a permanent magnetic field affecting the relay armature. This additional source of the magnetic field (called ‘‘polarizing’’) is usually made in the form of a permanent magnet.

  12. Microprocessor-based Relay The microprocessor-based relay is a small computer in which the output circuits have matched parameters with external current and voltage transformers, with a program stored in memory, allowing processing of input signals in such a way that operation of this or that type of protective relays can be modeled. With the help of a basic universal microprocessor, one can create any relay by just making certain changes in the program, at least that is how it used to be at the initial stage of development of microprocessor-based equipment.

  13. Sequence Relay • A sequence relay is sometimes called an alternator, stepper, step-by-step, flip-flop, or Impulse relay. The relay has the ability to open and close its contacts in a preset sequence. • All sequence relays use a ratchet or catch mechanism to cause their contacts to change state by repeated impulses to a single coil. Usually, but not always, one pulse will close a set of contacts, the next will open them, and so on, back and forth.

  14. Rotary Relay Rotary or motor-driven relays are relays in which forward movement of the armature and contacts is replaced by rotary movement. In fact, this is a standard multi-contact rotor switch with an electromagnetic drive instead of a manual one.

  15. Moving-coil Relay

  16. Relays of this type have a quite unusual external design, sometimes resembling a vacuum tube or a measuring device. It is only natural that such a relay resembles a measuring device because, in fact, it is a highly sensitive measuring mechanism, with very sensitive contacts. The functioning of this device is based on the interaction of the magnetic field of the permanent magnet with the current in the winding. The winding is wound around a light aluminum bobbin of rectangular shape (a frame) placed in the gap between the permanent magnet and the core ring.

  17. References: • http://www.electricalterminology.com/types-of-relays/v

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