Relay protection lockout relay

A lockout relay, also known as a master trip relay or ANSI code 86, is an auxiliary relay that latches its output to isolate a faulty section of a power system until manually reset.

Function and Purpose

Lockout relays serve as intermediaries between protective relays and circuit breakers, ensuring that when a fault is detected, the affected section is safely isolated. They do not sense faults themselves but receive trip signals from protective relays and then actuate multiple downstream devices, including breaker trip coils, alarms, indicator lights, and SCADA systems ( ). This latching function prevents the system from being re-energized until the fault is identified and corrected, enhancing safety and reliability ( ).

Operation

Lockout relays are typically electromechanical and have two coils:

• Operating coil: Energized by a protective relay to trip the relay and associated devices.
• Resetting coil: Energized manually or remotely to return the relay to its normal state. When the operating coil is energized, the relay moves to the tripped position, locking out the circuit. The relay remains in this state until manually reset, preventing automatic reclosure of breakers and ensuring that faults are addressed before restoring service ( ).

Applications

• Substations and switchgear: Lockout relays coordinate multiple protective relays and breakers, reducing wiring complexity and preventing damage to expensive protective relays ( ).
• Safety and monitoring: They activate alarms, indicator lamps, and interlocks to alert operators of faults ( ).
• Legacy and modern systems: While digital protection relays have evolved, the lockout relay's role as a latching intermediary remains critical ( ).

Testing and Maintenance

Regular functional testing is essential to ensure reliability. This includes:

• Secondary injection testing or simulating protective relay contacts to verify operation.
• Visual and electrical inspection of contacts, indicators, and downstream devices.
• Cleaning and lubrication of mechanical parts as per manufacturer guidelines ( ).

Key Advantages

• Provides isolation between protective relays and breaker trip coils, preventing relay contact damage.
• Simplifies wiring by consolidating multiple trip signals into a single relay.
• Ensures faulted sections remain de-energized until manual intervention, enhancing safety. In summary, the lockout relay is a critical component in power system protection, acting as a latching intermediary that ensures faults are safely isolated, reduces wiring complexity, and provides clear indications for operators before restoring service ( ).