Protective relays are commonly referred to by standard device numbers. 2 'Electrical Power System Device Function Numbers, Acronyms, and Contact Designations' deals with protective device function numbering and acronyms. These types of devices protect electrical systems and components from damage when an unwanted event occurs, such as an electrical. Power system protection relays can be categorized into different types of relays. Protective relays can be categorized based on their operating mechanisms into electromagnetic. The protection and control devices in electrical equipment can be referred to by numbers, with appropriate suffix letters when necessary, according to the functions they perform. The other is given in IEC 60617 and uses. In overcurrent, the four most used common types of protection relays are 50, 50N, 51, and 51N.
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