* “Types of Protective Relays and design requirements.” In this topic we will have a discussion on Design, mechanism and application of different types of relays*
And part 2a of this topic will give you a brief overview of the different types of relays that are to be discussed in the coming parts. There are three pain operating principles, electromechanical, solid state and
microprocessor. ELECTROMECHANICAL: It is a type of relays which sense the line currents and voltages by means of
electromagnetic induction and then quantifies it through analog means. SOLID STATE: Solid State Relays are semiconductor equivalents of the electromechanical relay and can
be used for protection and control without moving parts. MICROPROCESSOR: This type of relay that uses a microprocessor to analyze power system voltages,currents
and other quantities for the detection of faults in the industrial process system. These convert voltage and current to digital form and process the resulting measurements using the microprocessor. Now for operating characteristics we have many different
characteristics and we will discuss some of them including overcurrent relays, directional relays, distance protection impedance relays, reverse power flow relays, differential relays, thermal overload relays and pilot
relays. OVERCURRENT RELAYS: The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting
time. DIRECTIONAL RELAYS: They operate when the current flows in a particular direction
only. Principle of actuation is usually employed.
DISTANCE PROTECTION IMPEDENCE RELAY: This relay senses the impedance between the point of the fault and the point where relay is installed. REVERSE POWER FLOW RELAYS:
This type of relay is a directional protective relay that prevents power from flowing in the reverse direction.
DIFFERENTIAL RELAYS: The relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined
amount. THERMAL OVERLOAD RELAYS: These relays utilize the thermal properties of materials to detect a rise in temperature
from a certain limit and direct the contacts from one position to another. PILOT RELAYS: Pilot relaying refers to the communication network implemented on the high voltage
TX-line to transmit “trip or don’t trip” between two or more substations. *We will divide these 8 most common types relays in four parts, consisting of 2 types in each part.
In the second part that is part2(b), we will be discussing: OVERCURRENT RELAYS and DIRECTIONAL RELAYS. In the part 2(c) we will discuss,
DISTANCE OR IMPEDANCE RELAYS and REVERSE POWER FLOW RELAYS. In part 2(d), we will be discussing, DIFFERENTIAL RELAYS and TIME DELAY RELAYS.
And in the last part of the relay series that is part 2(e), we will discuss: THERMAL OVERLOAD RELAYS and PILOT RELAYS. *That’s all form this
part* *We hope that you have a continued interest in this topic and in this series as either a student or a professional. And we also hope that you find this content useful and
enlightening, please consider subscribing to generalpac.com or becoming a patron on patreon.com. GeneralPAC.com making power systems intuitive, open and free to everyone, everywhere, Thank you*