So, protection relays are mostly required in MV (medium voltage) and HV (high voltage panels) where it's combination with the breaker will prevent overcurrent (because a relay can just detect and give a signal, but cannot trip the circuit, which requires the mechanical. So, protection relays are mostly required in MV (medium voltage) and HV (high voltage panels) where it's combination with the breaker will prevent overcurrent (because a relay can just detect and give a signal, but cannot trip the circuit, which requires the mechanical. A voltage protection relay system is a necessary component of any electrical setup. It prevents safety hazards and damage to equipment. Many industries use voltage protection relay systems, especially those in high-voltage. 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 continue to run under normal conditions. : 4 The first. The objective of this presentation is to convey a basic understanding of protective relays to an audience of engineers already familiar with low voltage protective device coordination. Their primary purpose is to identify critical conditions such as under-voltage and over-voltage and initiate circuit disconnection, as well as alarming affected user circuits. What are their uses, kinds and.