Lightning Arrester Leakage Current Monitoring: Gist of Technical Guidelines, Standards, Procedure & Advanced Insights

High voltage electrical discharge illuminates the sky, showcasing the immense power of lightning as a natural electrical phenomenon

1. Introduction

Lightning arrestors (LAs) are critical protective devices used in electrical substations to safeguard equipment from high-voltage transients caused by lightning strikes and switching surges. Installed at strategic points such as transformer terminals, incoming feeders, and busbars, LAs provide a low-impedance path to ground for the surge voltage, thereby protecting insulation and preventing equipment failure. Typically, metal oxide varistor (MOV)-based arrestors with zinc oxide discs are used due to their excellent non-linear voltage-current characteristics and fast response time. The construction includes a weatherproof porcelain or polymeric housing, internal ZnO blocks, and grading rings to control electric field distribution. The design and application of lightning arrestors in substations are governed by standards such as IEC 60099-4, IEEE C62.11, and IS 3070 (Part 3), which specify performance requirements including discharge capability, residual voltage, and energy absorption. Regulatory frameworks such as CEA Technical Standards for Construction of Electrical Plants and Electric Lines Regulations and CEA Grid Connectivity Regulations emphasize the mandatory installation of lightning protection systems to ensure grid reliability and safety.

2. Why Monitor LA Leakage Current?

2.1 Benefits of Leakage Monitoring

• Early Fault Detection: Rising resistive current indicates degradation of ZnO elements.

• Prevention of Equipment Failure: Prevents catastrophic failures that can damage adjacent equipment like transformers or CTs.

• Uninterrupted System Operation: Online test—no need to shut down the system.

• Data Trends & Predictive Maintenance: Enables data logging and future condition forecasting.

• Enhanced Safety: Alerts to impending arrester failures, reducing risks to personnel.

• Cost Savings: Reduces forced outages and unscheduled maintenance.

2.2 Drawbacks of Not Testing

• Undetected Degradation: ZnO block aging remains invisible in total current readings.

• Unplanned Failures: Leads to collateral damage and unsafe operating conditions.

• Inefficient Maintenance Planning: Unable to prioritize replacements or maintenance scheduling.

• Non-compliance with Regulations: Risk of penalty and liability under CEA regulations.

3. Regulatory Framework and Standards

3.1 International Standards

IEC 60099-5: Recommended Practices for Monitoring of Surge Arresters in Service

• Clause 7.2.3: "The measurement of the resistive component of the leakage current should be done using the third harmonic analysis or voltage peak method."

• Clause 9: Discusses condition assessment thresholds and deterioration criteria for in-service arresters.

3.2 Indian Standards

IS 3070 Part 3:1993 - Metal-Oxide Surge Arresters Without Gaps

• Clause 3.1: "Metal-oxide arresters without spark gaps shall be capable of limiting voltage and absorbing energy without internal flashover."

• Clause 7: Details type and routine tests including insulation withstand, residual voltage, discharge current.

• Clause 10: Establishes the requirement for leakage current measurement during service as part of condition monitoring.

  
  

RDSO Guidelines (Indian Railways)

• Section 4.2: "Resistive leakage current greater than 500 µA indicates severe degradation and warrants removal from service."

• Section 4.1: "Leakage current between 350-500 µA shall be monitored periodically."

GEM Technical Specification - Leakage Current Meters

• Excerpt: "The measurement shall be based on the principle of 3rd harmonic resistive leakage current with real-time harmonic compensation as per IEC 60099-5."

3.3 CEA Regulations (India)

CEA (Measures Relating to Safety and Electric Supply), 2010

• Regulation 85: "Every consumer or supplier shall maintain test records... including leakage currents for inspection."

CEA Guidelines for O&M Benchmarking (2025)

• Section 7.3: "Impulse withstand, leakage current monitoring, and visible signs of deterioration must be checked periodically as part of LA condition monitoring."

CEA Draft Guidelines on Type-Test Validity (2024)

• Lists lightning arresters among major equipment requiring periodic health assessment and compliance to type-test schedules.

4. LA Leakage Current Test Methods

4.1 Third-Harmonic Resistive Leakage Current Method (IEC 60099-5, Method B1/B2)

Test Setup

• Clamp-on current transformer (CT) placed on the earth lead of the arrester.

• Optional field probe near the arrester to detect harmonic voltage.

Procedure

1. Connect CT and field probe securely.

2. Begin online test; arrester must be energized.

3. Record total leakage current.

4. Isolate 3rd-harmonic resistive component using internal algorithms.

5. Apply correction for harmonics, temperature, and system voltage.

6. Compare results to accepted thresholds.

7. Record, report, and trend the data.

4.2 Voltage-Peak Method (IEC 60099-5, Method A1)

Procedure

1. Connect voltage reference probe (typically from PT secondary).

2. Measure leakage current at the voltage waveform's peak.

3. Determine resistive component from peak amplitude.

4. Correct and analyze data against benchmarks

5. Interpretation of Test Results

Leakage Current (µA)	Condition	Action Required
< 350	Normal	Continue in service
350–500	Degrading	Monitor periodically
> 500	Critical	Immediate removal required

6. Safety Precautions During Testing

• Ensure testing is done by qualified and trained personnel.

• Verify all test equipment is calibrated and in good working condition.

• Always wear appropriate PPE including insulated gloves, face shield, and arc-flash suit.

• Confirm that the arrester is properly earthed and test point is accessible.

• Maintain safe distance from energized parts during testing.

• Use insulated tools and rated CT probes.

• Confirm environmental safety (no water logging, slippery surfaces, or risk of accidental contact).

7. Introduction to latest testing solutions from SURGETEC

SURGETEC bring to an advanced arrester monitoring solution designed for precision, predictive maintenance, and continuous diagnostics.

Advantages of SURGETEC solutions over Conventional Testing

Feature	SURGETEC	Conventional Test Kits
Measurement Accuracy	µA-level resolution with noise suppression	Manual filtering, susceptible to EMI
Compensation Capabilities	Full auto-compensation for voltage/temp/harmonics	Manual or semi-automatic
Monitoring Mode	Continuous / Real-time	Periodic
Predictive Analytics	Health index, trend analysis, alerts	Manual data review
Safety	Remote monitoring possible	Field presence required

Resistive Current Analyzer for Surge Arrester

8. Summary and Recommendations

1. Leakage current monitoring is vital for reliable arrester operation.

2. IEC 60099-5 and IS 3070-3 provide comprehensive test methodologies.

3. Thresholds must be followed as per RDSO and CEA recommendations.

4. Tests must be conducted with all safety protocols in place.

5. Advanced solutions like SURGETEC offer predictive and real-time insights for enhanced reliability.

6. Records must be retained as per CEA Regulation 85.

9. References

1. IS 3070 Part 3:1993 - Metal Oxide Surge Arresters Without Gaps

2. IEC 60099-5 - Surge Arresters: Monitoring in Service

3. RDSO Pocket Book on Condition Monitoring of Lightning Arresters

4. GEM Technical Specification on Leakage Current Meters

5. CEA (Measures Relating to Safety and Electric Supply), 2010

6. CEA Guidelines for Benchmarking O&M of Distribution Utilities

7. CEA Draft Guidelines on Type-Test Validity, Nov 2024

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