Relay Protection Types in Substations: A Complete Guide

(1) Generator Protection:
Generator protection covers: phase-to-phase short circuits in stator windings, stator ground faults, inter-turn short circuits in stator windings, external short circuits, symmetrical overload, stator overvoltage, single- and double-point grounding in the excitation circuit, and loss of excitation. Tripping actions include shutdown, islanding, limiting fault impact, and alarm signaling.

(2) Transformer Protection:
Power transformer protection includes: phase-to-phase short circuits in windings and their leads, single-phase ground faults on directly grounded neutral sides, inter-turn short circuits, overcurrent due to external short circuits, overcurrent and neutral overvoltage caused by external ground faults in directly grounded systems, overload, low oil level, high winding temperature, excessive tank pressure, and cooling system failure.

(3) Line Protection:
Line protection varies based on voltage level, neutral grounding method, and line type (cable or overhead). Common protections include: phase-to-phase short circuits, single-phase ground faults, single-phase grounding, and overload.

(4) Busbar Protection:
Dedicated busbar protection should be installed for busbars in power plants and critical substations.

(5) Capacitor Protection:
Shunt capacitor protection covers: internal capacitor faults and lead short circuits, short circuits in interconnecting leads between capacitor banks, overvoltage after faulty capacitor removal, bank overvoltage, and loss of bus voltage.

(6) High-Voltage Motor Protection:
High-voltage motor protection includes: stator phase-to-phase short circuits, stator single-phase ground faults, stator overload, undervoltage, loss of synchronism, loss of excitation (for synchronous motors), and non-synchronous inrush current.

Written by: A senior protection engineer with 12 years of experience in Substation design (IEC/GB standards).