What are the main types of high-voltage lightning arresters and causes of failure?

High-voltage lightning arresters are crucial protective devices in power systems, mainly used to protect power generation, transformation, transmission and power consumption equipment from damage caused by lightning overvoltage and operational overvoltage.

What is a high-voltage lightning arrester?

 

Core Definition: A high-voltage lightning arrester is a voltage-limiting device connected in parallel between the protected equipment (such as transformers, switchgear, etc.) and the ground. When the system is operating normally, it exhibits a high resistance state, equivalent to an open circuit, which does not affect system operation. When a dangerous overvoltage (such as a lightning strike) occurs and reaches its operating voltage, it quickly exhibits a low resistance state, discharging the significant overvoltage current to the ground, thereby limiting the voltage on the protected equipment to a safe level. Once the overvoltage subsides, it automatically returns to its high resistance state, ensuring continued normal operation of the system.

To put it simply, it's like a "voltage-sensitive safety valve." Normally closed, it rapidly opens to relieve pressure when the pressure (voltage) becomes excessive, and automatically closes once the pressure returns to normal.

 

Main Types

The development of high-voltage surge arresters has gone through several stages, with the metal oxide surge arrester (MOA) currently the mainstream.

Tube-type surge arrester:

Features: An early product that utilizes gas-generating materials to extinguish arcs by generating gas in response to arcing.

Current Status: Poor protection performance has led to its near obsolescence, with only some older lines or specific applications.

Silicon Carbide Surge Arrester (Valve-type Surge Arrester):

Features: Consists of multiple silicon carbide resistor valve plates connected in series and requires a series gap for use.

Working Principle: During normal operation, the gap isolates the valve plate from the system. When an overvoltage breaks down the gap, the valve plate exhibits nonlinear resistance, dissipating the current.

Current Status: This was the mainstream product before the advent of MOA, and is now being gradually replaced by the more superior MOA.

Metal Oxide Arrester (MOA):

Features: This is currently the most mainstream and widely used type. Its core component is a zinc oxide (ZnO) resistor valve disc.

Operating Principle: The ZnO valve disc has an extremely excellent nonlinear volt-ampere characteristic. Simply put:

Under normal voltage: The resistance is extremely high, and the leakage current is extremely low (microamperes), equivalent to an insulator.

Under overvoltage: The resistance becomes extremely low instantaneously (within nanoseconds), capable of dissipating thousands of amperes of lightning current while limiting the voltage to a level that the equipment can withstand.

Advantages:

Gapless: Simple structure, extremely fast response.

Excellent protection performance: Low residual voltage, effectively protecting modern equipment with more sophisticated insulation levels.

Large current capacity: Withstands repeated lightning currents and switching overcurrent surges.

Strong withstand capability: Stable performance and long service life.

Classifications:

Power station type: Used to protect critical equipment in power plants and substations, such as transformers and circuit breakers. Offers the highest current capacity.

Line type: Installed on transmission lines to protect line insulators from lightning strikes.

Distribution type: Used in medium and low voltage distribution systems to protect distribution transformers, switchgear, etc.

Shunt compensation capacitor bank protection type: Specifically designed to protect capacitor banks, capable of withstanding frequent switching overvoltages.

Motor type: Used to protect rotating electrical machines (such as motors and generators), requiring higher protection characteristics (residual voltage).

 

Core Functions and Roles

Lightning overvoltage limitation: Dissipates lightning waves caused by direct or induced lightning strikes. This is its most basic and important function.

Operational overvoltage limitation: Dissipates overvoltages caused by internal system operations such as circuit breaker opening and closing, ground faults, etc.

Insulation protection: By limiting overvoltages to safe levels, it protects the primary and longitudinal insulation of electrical equipment (especially the costly main transformer) from breakdown and damage.

System stability maintenance: By quickly clearing overvoltage faults, it contributes to the safe and stable operation of the power system.

 

Key Parameters

System Rated Voltage: The nominal voltage of the power system to which the arrester is connected.

Continuous Operating Voltage: The effective value of the power frequency voltage permitted to be applied across the arrester over a long period of time. This value must be greater than the system's highest operating phase voltage.

Nominal Discharge Current: The peak value of the lightning current with an 8/20μs waveform used to classify arrester ratings, such as 5kA, 10kA, etc.

Residual Voltage: The most important protection parameter. This refers to the peak voltage across the arrester when the discharge current passes through it. The lower the residual voltage, the better the protection.

DC Reference Voltage: The voltage across the arrester measured with a DC reference current of 1mA. This parameter is often used to detect moisture or aging in the field.

Impulse Discharge Volt-Second Characteristics: This describes the discharge characteristics of an arrester under impulse voltages of varying wave front steepness. It must always be below the insulation withstand level of the protected equipment.

 

Operation, Maintenance, and Monitoring

Daily Inspection: Check the exterior for damage and contamination, check the discharge counter's number of trips and record the leakage current, and verify proper sealing.

Preventive Testing:

Measure the DC reference voltage (U1mA) and leakage current (at 75% of U1mA): This is the primary method for determining whether the arrester is aging or exposed to moisture. If U1mA drops significantly or the leakage current at 75% of U1mA increases significantly, the arrester's performance has deteriorated and requires replacement.

Insulation Resistance Testing: This helps determine internal moisture.

Online Monitoring: Many arresters are equipped with an online leakage current monitor that provides real-time monitoring of the total current and resistive current components, enabling early detection of defects.

 

Common Failures and Causes

Moisture: Poor sealing allows moisture to enter the interior, which is one of the most common causes of arrester failure.

Aging: Long-term exposure to operating voltage and overvoltage shocks causes the zinc oxide valve plate to gradually deteriorate in performance, increasing leakage current and eventually causing thermal breakdown and damage.

Overload Damage: Suffering from a surge of current exceeding its designed current capacity (such as a severe direct lightning strike).

Product Quality Issues: Uneven valve plate performance, internal structural defects, etc.

Improper installation or mechanical damage.

 

Summary

High-voltage surge arresters, particularly metal oxide surge arresters (MOSAs), are indispensable guardians of modern power systems. Their fast, reliable, nonlinear voltage-limiting action ensures the safety of expensive and critical electrical equipment throughout power generation, transmission, and distribution, playing a vital role in improving power supply reliability and system stability. Proper selection, installation, monitoring, and maintenance are crucial to ensuring their effective performance.

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