Lock out relay (LOR) in electrical substation

Introduction to Lockout Relay (LOR)

When electrical faults happen in power systems, safety devices work to protect equipment and people. One of the most important safety devices is the Lockout relay (LOR), also known by its code number ANSI 86.

Think of the lockout relay (LOR) as a safety lock on your electrical system. Its job is simple but critical: once a circuit breaker opens due to a dangerous fault, the lockout relay (LOR) keeps it locked in the “OFF” position. No one can turn the circuit breaker back on—not even by accident—until a trained electrician checks the system, fixes the problem, and manually unlocks the relay.

This simple mechanism prevents a very dangerous situation: turning power back on when a fault still exists.

What Exactly is a Lockout Relay (LOR)?

The lockout relay (LOR), also known as the Master Trip Relay or 86 lockout relay (ANSI 86), is a protective device that keeps circuit breakers in an open position after severe electrical faults occur. Unlike standard protective relays that simply initiate a trip command, the lockout relay adds an additional layer of security by preventing any reclosing attempts—whether manual or automatic—until deliberate human intervention occurs.

The purpose of a lockout relay (LOR) is to provide fail-safe protection by ensuring that electrical circuits cannot be accidentally re-energized while dangerous fault conditions still exist in the system.

The Critical Problem It Solves

Imagine this scenario: An overcurrent fault triggers your protection relay, which correctly sends a trip command to the circuit breaker’s trip coil. The breaker opens, disconnecting the faulty section. However, what happens if someone accidentally issues a closing command to that circuit breaker before the underlying fault has been investigated and repaired?

Without a lockout relay, the breaker would close directly onto the faulty condition, potentially causing:

• Severe damage to the circuit breaker itself
• Escalation of the original fault
• Risk of equipment fire or explosion
• Danger to personnel working on the system

The 86 lockout relay eliminates this dangerous possibility entirely.

How Does the Lockout Relay Function?

Understanding Lockout Relay Function

The lockout relay function is based on a mechanical latching mechanism combined with electrical coils. This design ensures that once activated, the relay physically locks into position and cannot be released without manual intervention.

Internal Construction

The 86 lockout relay operates through a dual-coil mechanism:

1. Operating Coil (Trip Coil)

• Connects in series with the normally open (NO) contact that represents the trip command from protective relays
• When energized, it mechanically latches the relay into the lockout position
• Simultaneously opens the normally closed (NC) contacts in the closing circuit

2. Resetting Coil

• Energized through a dedicated reset push button or mechanical handle
• Only a qualified technician can activate this coil
• Returns the relay to its normal ready state after fault clearance

Operating Sequence Explained

Here’s the step-by-step operation when a fault occurs:

1. Fault Detection: A substation fault occurs in the power system
2. Protection Activation: The appropriate protection relay detects the abnormal condition
3. Trip Command Issued: The protection relay closes its NO contact
4. Lockout Engagement: Current flows through the operating coil of the 86 relay
5. Mechanical Latching: The relay mechanically locks into position
6. Closing Circuit Interrupted: The NC contact in the breaker closing circuit opens
7. Circuit Breaker Trips: The breaker receives the trip signal and opens
8. Lockout Maintained: Even after the trip signal ends, the relay remains latched

The circuit breaker now cannot close—regardless of closing commands—until a technician physically resets the lockout relay after confirming the fault has been eliminated.

Typical Applications in Power Systems

Substation Protection

In electrical substations, lockout relays provide critical protection for:

• Transformer Differential Faults: When internal transformer faults occur, the 86 relay prevents re-energization that could lead to transformer explosion
• Busbar Protection: Severe bus faults require thorough inspection before restoration
• Breaker Failure Protection: If a circuit breaker fails to operate, the lockout relay can trip multiple backup breakers

Power Generation Facilities

Power plants utilize lockout relays extensively for:

• Turbine-Generator Protection: Mechanical or electrical abnormalities in rotating machinery
• Multiple Breaker Coordination: Single fault conditions requiring simultaneous tripping of several breakers
• Critical Equipment Isolation: Ensuring expensive generation equipment remains de-energized during fault conditions

Industrial Installations

Manufacturing facilities and industrial plants depend on lockout relays for:

• Protecting high-value process equipment
• Coordinating protection schemes across complex electrical networks
• Meeting safety compliance standards for electrical safety

Reset Mechanisms

How is a Lockout Relay in a Control Circuit Reset?

Resetting a lockout relay in a control circuit requires deliberate manual action by qualified personnel. This is a critical safety feature that ensures faults are properly investigated before power restoration. The 86 lockout relay typically offers two primary reset methods:

Mechanical Handle Reset

• Physical lever or rotary handle on the relay faceplate
• Provides tactile confirmation of reset action
• No electrical power required for reset operation

Electrical Push Button Reset

• Remote reset capability through control circuits
• Energizes the reset coil electrically
• Often includes SCADA interface capability for monitoring

Lockout Relay Testing Procedures

Regular testing of lockout relays ensures their reliability when protection is needed most. Here’s a comprehensive testing protocol based on industry standards:

Pre-Test Mechanical Inspection

Before electrical testing begins, conduct a thorough mechanical examination:

• Verify freedom of movement in all mechanical components
• Check for corrosion, dirt, or obstruction
• Ensure reset mechanism operates smoothly
• Inspect contact surfaces for pitting or burning

Electrical Testing Steps

Step 1: Test Setup

• Carefully remove the relay from its installed case
• Connect the relay to calibrated test equipment following the manufacturer’s wiring diagram
• Verify all test connections before applying voltage

Step 2: Pick-up Voltage Test

• Gradually increase applied voltage to the operating coil
• Record the exact voltage at which the relay mechanically latches
• Document the contact operation time (typically measured in milliseconds)
• Compare against manufacturer specifications

Step 3: Drop-off Voltage Measurement

• After the relay has operated, gradually decrease voltage from the pick-up value
• Record the voltage level at which the relay releases (drop-off voltage)
• Note the contact return time

Step 4: Reset Ratio Calculation

• Calculate the reset ratio using the formula:

Reset Ratio = (Vdrop-off / Vpick-up) × 100%

• A healthy relay typically exhibits a reset ratio between 90-95%
• Significant deviation indicates mechanical wear or electrical issues

Step 5: Coil Resistance Verification

• Measure the DC resistance of both operating and reset coils
• Compare measurements against nameplate values
• Resistance variations exceeding 10% warrant investigation

Step 6: Reset Mechanism Verification

• Test both mechanical and electrical reset functions
• Ensure positive engagement and release
• Verify reset indication (if equipped)

Step 7: Contact Integrity Testing

• Measure contact resistance using a micro-ohmmeter
• Check continuity of all contact circuits
• Test insulation resistance between isolated circuits
• Verify proper make-and-break sequences

Testing Frequency

According to IEEE standards, lockout relays should undergo:

• Annual visual inspection: Check for physical damage or environmental deterioration
• Triennial functional testing: Complete electrical testing as described above
• Post-fault testing: After any lockout operation, verify proper function before return to service

Lockout Relay Wiring Diagram and Configuration

Understanding the lockout relay wiring diagram is essential for proper installation and operation. The wiring configuration connects the relay into your control circuit in a way that intercepts both trip signals and closing commands.

Basic Wiring Components

A typical 86t lockout relay (where “t” indicates trip function) wiring diagram includes these key connections:

1. Operating Coil Circuit (Trip Input)

• Connects in series with protective relay trip contacts
• Receives 125V DC or 48V DC control power (depending on system design)
• Wire terminals typically labeled as “TC” or “Trip Coil”
• Multiple protection relays can be connected in parallel to trip the same lockout relay

2. Trip Output Circuit

• NC (Normally Closed) contacts interrupt the circuit breaker closing circuit
• These contacts open when the lockout relay operates
• Prevents any closing command from reaching the breaker
• Usually rated for control circuit voltage (125V DC typical)

3. Reset Coil Circuit

• Connected to a manual reset push button or switch
• Requires separate control power source
• Terminals marked as “RC” or “Reset Coil”
• Often includes a series contact to prevent inadvertent reset

4. Auxiliary Contacts for Alarms

• Additional contacts provide status indication
• Connected to annunciator panels or SCADA systems
• Help operators identify which relay has operated
• Typically provides both NO and NC contact options

Lockout Relay Wiring Diagram Example

Here’s a simplified description of a typical control circuit with lockout relay:

Protection Relay Trip Contact → 86 Operating Coil → Return to DC Negative

DC Positive → Circuit Breaker Close Push Button → 86 NC Contact → Breaker Closing Coil → DC Negative

DC Positive → Manual Reset Push Button → 86 Reset Coil → DC Negative

In this configuration:

• When a fault occurs, the protection relay energizes the 86 operating coil
• The lockout relay latches mechanically
• The NC contact opens, breaking the closing circuit
• The breaker cannot close until the reset button is pressed
• After reset, the NC contact closes again, restoring normal control

Critical Wiring Considerations

When installing a lockout relay in your control circuit:

• Never bypass the lockout contacts – This defeats the safety purpose
• Use proper wire sizing – Control circuits typically use 14 AWG minimum
• Label all connections clearly – Aids troubleshooting and maintenance
• Test the circuit – Verify proper operation before energizing equipment
• Follow manufacturer diagrams – Each relay model may have specific requirements
• Maintain isolation – Keep trip and close circuits properly separated

Common Installation Considerations

Panel Mounting

Most lockout relay devices mount on standard 35mm DIN rail or directly to panel surfaces. Considerations include:

• Accessibility for operators performing resets
• Visibility of mechanical indicators
• Protection from environmental factors
• Adequate spacing for termination access

Advantages of Implementing Lockout Relays

Safety Enhancement

The primary benefit remains personnel safety. By preventing inadvertent re-energization, lockout relays protect:

• Maintenance technicians investigating faults
• Operations staff working in affected areas
• The general public near utility installations

Equipment Protection

Expensive power system equipment gains an additional protection layer:

• Power transformers worth hundreds of thousands of dollars
• Circuit breakers with limited fault interruption capability
• Generators and rotating machinery
• Control and instrumentation systems

Operational Reliability

Well-designed lockout schemes improve overall system reliability by:

• Ensuring thorough fault investigation before restoration
• Preventing damage escalation
• Reducing unplanned outages
• Supporting proper fault analysis procedures

Troubleshooting Common Issues

Relay Fails to Operate

Possible causes:

• Insufficient voltage to operating coil
• Mechanical binding or obstruction
• Open circuit in trip wiring
• Degraded coil insulation

Relay Fails to Reset

Investigation areas:

• Mechanical linkage issues
• Inadequate reset coil voltage
• Stuck contacts or latch mechanism
• Reset circuit wiring problems

Nuisance Lockouts

If the relay operates without legitimate faults:

• Check for wiring short circuits
• Investigate spurious protection relay operations
• Verify proper relay settings
• Review recent system modifications

Conclusion

The Lockout Relay (ANSI 86) solves a critical safety problem: it physically prevents a circuit breaker from automatically closing again after it trips due to a fault. This ensures a person must check the system before power is restored.

This device is essential in power plants, substations, and industrial facilities. It prevents equipment damage, protects workers, and ensures safe system restoration.