Classifications of relay protection device
1. Classified based on the protected targets
Power line protection , generator protection, transformer protection, capacitor protection, reactor protection, motor protection, busbar protection and so on.
2. Based on protection principles
Current protection , voltage protection, distance protection, differential protection, direction protection and zero sequence protection and so on.
3. According to fault type
Phase-to-phase short-circuit protection, grounding fault protection, interturn short circuit protection, line break protection, step loss protection, field loss protection, and overexcited protection.
4. According to the functions of protection
Main protection, backup protection and auxiliary protection.
Main protection: to meet the requirements of stable system and equipment safety and isolate fault elements quickly.
Backup protection: to cut/ clear fault when main protection or CB refuses to act.
Backup protection include remote backup protection which means use the protection from near electrical equipment or line and near backup protection which mean use protection of its electrical equipment or line.
Auxiliary protection is to make up main protection and backup protection or when main protection and backup protection are out of service.