Leakage Current in Lightning Arrester: Best Guide

Leakage current in lightning arrester is one of the most overlooked yet critical aspects of power system safety. It refers to the small current that flows through the arrester even when there is no lightning event. Though it may seem insignificant, this current can reveal important information about the health of the arrester and the insulation system.

In high-voltage environments, understanding and controlling leakage current is essential. Lightning arresters are installed to protect equipment from high transient voltages caused by lightning or switching surges. These devices are supposed to remain non-conductive during normal operations and conduct only when a surge occurs. However, they allow a small continuous current called leakage current. Let’s explore what causes this current, its effects, measurement methods, and preventive strategies.

What is Leakage Current in Lightning Arrester?

Leakage current in lightning arrester is the continuous flow of electrical charge across the insulation or surface of the arrester when it is energized. It occurs even in the absence of surge conditions. This current flows mainly through the non-linear resistor elements and is influenced by environmental conditions like humidity, pollution, and temperature.

Lightning arresters are made of metal oxide varistors (MOVs), typically zinc oxide. These materials are highly non-linear, meaning they conduct very little current under normal voltage but allow large currents during surges. Still, some current leaks through even in standby mode.

This leakage current is not a fault current. But if it increases beyond acceptable levels, it may indicate a deteriorating arrester. Over time, high leakage current can lead to thermal stress and eventual failure.

Why is Leakage Current in Lightning Arrester Important?

The significance of leakage current in lightning arrester lies in its role as an early indicator of equipment degradation. Continuous monitoring helps maintenance teams detect insulation aging, moisture ingress, or internal faults. If left unchecked, high leakage current can lead to complete arrester breakdown and system failures.

The performance of surge arresters is strongly linked to their leakage behavior. Excessive current can cause thermal runaway, especially in polluted environments. That’s why utilities often use leakage current values as benchmarks in condition-based maintenance programs.

Also, high leakage current can lead to nuisance tripping of protection relays. This results in unnecessary outages and affects the reliability of the power system.

Causes of Leakage Current in Lightning Arrester

There are several factors that contribute to leakage current in lightning arrester. The key causes include:

1. Surface Pollution: Dust, salt, and industrial pollutants form a conductive film on the arrester’s surface, increasing leakage current.
2. Humidity and Moisture: Water droplets reduce surface resistance and enhance current flow.
3. Aging of MOV Blocks: Continuous electrical stress causes microcracks and reduces insulation strength.
4. High System Voltage: Slight overvoltages over time lead to increased leakage.
5. Temperature Rise: Thermal conditions affect the conductivity of MOV materials.

All these elements can collectively or independently cause a rise in leakage current, leading to increased thermal stress and potential arrester failure.

Types of Leakage Current in Lightning Arrester

Leakage current in lightning arrester can be broadly classified into two types: capacitive and resistive.

Capacitive current is dominant immediately after energization but fades quickly. Resistive current, however, remains during normal operation and is more critical for condition monitoring. Accurate separation of these components is vital during testing.

If you’re interested in other similar topics, our Leakage Current in Capacitor Guide offers deep insights into capacitor behavior under similar conditions.

Measurement of Leakage Current in Lightning Arrester

Measuring leakage current in lightning arrester is an important maintenance practice. Utilities often use clamp-on meters or install permanent monitoring devices to capture current data. The measurement should ideally focus on the resistive component.

Techniques include:

• Online Monitoring: Real-time measurement using sensors around the arrester’s ground connection.
• Offline Testing: Insulation resistance and leakage current are measured when the system is de-energized.
• Harmonic Analysis: Differentiates between capacitive and resistive current components.

Accuracy is essential. Improper methods may capture external leakage paths and give incorrect readings. Data should be compared to base values obtained during commissioning.

Acceptable Values of Leakage Current in Lightning Arrester

The acceptable leakage current in lightning arrester depends on the voltage class, environment, and design. However, general guidelines are as follows:

Any value exceeding these thresholds must be investigated. A progressive increase in current often signals internal degradation or external contamination.

How to Reduce Leakage Current in Lightning Arrester

Reducing leakage current in lightning arrester involves a combination of good design, proper installation, and regular maintenance. Here are some practical strategies:

• Use Silicone Rubber Housing: Better hydrophobic properties reduce surface leakage.
• Install Arrester Sheds or Creepage Extensions: Improve insulation distance and reduce pollution effects.
• Routine Cleaning: Especially in coastal and industrial areas.
• Use Monitoring Devices: Track trends and set alarms for abnormal rise.

By following these steps, system reliability is enhanced and unplanned outages are minimized.

Leakage Current Monitoring Techniques

Monitoring leakage current in lightning arrester has evolved over time. Modern systems use digital sensors with remote data access. Key technologies include:

• Optical Current Transformers: Provide accurate and safe measurement.
• Wireless Data Loggers: Help monitor arresters in inaccessible locations.
• SCADA Integration: Allows remote alerts and condition-based alerts.

The goal is to track trends, not just absolute values. A sudden rise in resistive current, even within limits, may be more alarming than a high but stable reading.

Impact of Leakage Current on System Health

If leakage current in lightning arrester increases without attention, the system can suffer. The most common impacts include:

• Arrester Failure: Excess heat breaks down MOV blocks.
• Insulation Damage: High leakage current may create corona and partial discharges.
• Protection Malfunctions: High current can mimic fault current and cause false trips.
• Energy Loss: While small per unit, the cumulative power loss across multiple units is significant.

These issues may not show up immediately but lead to long-term reliability problems.

Leakage Current in Lightning Arrester vs. Other Components

To put it in perspective, leakage current in lightning arrester is similar in concept to Leakage Current in Capacitor or semiconductors. In capacitors, leakage is a result of dielectric breakdown, while in arresters, it’s the conduction through MOVs. Likewise, in transistors, the Leakage Current Formula for Transistor helps calculate off-state current losses.

Understanding these parallels helps engineers build holistic condition monitoring programs.

Best Practices for Managing Leakage Current

Managing leakage current in lightning arrester doesn’t have to be complex. Here are some concise recommendations:

• Record base leakage current values during commissioning.
• Monitor temperature and humidity data along with current.
• Replace arresters showing fast-rising resistive current.
• Clean arresters periodically in polluted zones.
• Integrate condition data into maintenance dashboards.

These small steps go a long way in reducing unexpected failures and maintaining system integrity.

Conclusion

Leakage current in lightning arrester is more than just a small current on the side. It’s a vital diagnostic tool for power engineers. It indicates the health of your lightning protection system and helps you catch early signs of failure.

Ignoring this current is a mistake many systems cannot afford. Whether you’re working in distribution networks or high-voltage substations, keeping an eye on leakage current should be standard practice. Invest in monitoring tools, compare historical data, and maintain cleanliness.

When done right, this ensures longer arrester life, fewer outages, and better power quality. So, the next time you look at a surge arrester, remember — even the smallest current can speak volumes about your system’s future.

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