<p style="text-align:justify"><span style="font-size:14px">Electromagnetic or Electromechanical Relays: They use principles of electromagnetism to produce torque. The parts of the relay are manufactured using mechanical components like core, spring, back-stops, bearing etc. These relays are suffering from many problems like friction, low torque, high burden, high power consumption of auxiliary circuits, transient overreach, large overshoot time, low drop-off to pick-up ratio (resetting ratio), very large resetting time etc. These problems have rendered the electromagnetic relays just useless and obsolete. Relay manufacturers have discontinued manufacturing and users are slowly retrofitting the old installations containing electromagnetic relays by modern numerical relays.</span></p>

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<p style="text-align:justify"><span style="font-size:14px">With the advent of ICs (integrated circuits) and chips, the static protective relays have replaced the electromechanical relays. They have many advantages which we will be talking about. Static relays are the second generation relays.</span></p>

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<p style="text-align:justify"><span style="font-size:14px">The evolution of the numerical relays began with the development of microprocessors and digital computers in the early 1960s. The pioneer in this field of computer relaying is Rockfeller who wrote his master&rsquo;s dissertation dedicating a hypothetical digital computer for protecting a large substation. We will also dedicate a full chapter for understanding numerical relays. Numerical relays are the third generation relays. </span></p>