Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function (time-based, current, voltage). : 4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as. To attain the desired reliability, the power system network is divided into two different protection zones. They are generator protection, transformer protection, bus protection, transmission line protection and feeder. A protective relay is an electronic device used in power systems to monitor and analyze electrical parameters, such as current, voltage, and frequency, and to take action to protect electrical equipment and ensure system stability. Its main purpose is to safeguard electrical equipment like transformers, generators, and transmission lines from damage due to. Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 2 Abstract: Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system.