Surge Arrester Structure and Electrical Testing Technology

Master the internal structure of Zinc Oxide Arresters (MOA) and critical electrical tests including DC reference voltage and leakage current for power systems.

Vziman

Field: Manufacturing

10Year<

China

Add us on Google

1.Critical Role of Surge Arresters in Power System Overvoltage Protection

The surge arrester serves as the primary line of defense against overvoltage in power systems. Its operational status directly determines the insulation safety of major equipment such as transformers, motors, and switchgear. Zinc Oxide Arresters (MOA), with their superior non-linear voltage-current characteristics, have become the most widely used protective devices in modern grids. Deeply understanding their internal configuration and performing scientific preventive tests are essential to identifying hidden defects like valve aging or seal failure, ensuring long-term grid stability.

2.Internal Configuration and Electrical Characteristic Models of MOA

2.1 Core Definitions

Zinc Oxide Arrester (MOA): A protective device utilizing the non-linear resistance of zinc oxide valves to limit overvoltage. It maintains a high-impedance state at normal operating voltage and rapidly transitions to a low-impedance state during overvoltage to clamp the residual voltage within safe limits.

2.2 Zinc Oxide Valve V-I Characteristic:

I=k⋅U^α

Description:
This relationship describes the non-linear current and voltage behavior of zinc oxide valves. $I$ is the current flowing through the valve, $U$ is the applied voltage, and $k$ is a material constant. $α$ (the non-linearity coefficient) is the core performance metric; a higher value indicates a stronger voltage-clamping capability during overvoltage and lower power loss at continuous operating voltage.

2.3 Resistive Current Component:

I_r=I⋅cosϕ

Description:
The total current $I$ in an arrester consists of a capacitive component and a resistive component $I_{r}$ . By measuring the phase angle $ϕ$ , the resistive current representing valve energy consumption and aging status can be isolated. A significant increase in $I_{r}$ is a direct warning sign of moisture ingress or valve degradation.

2.4 Structural Classification

Insulation Housing: Categorized into porcelain and composite (silicone rubber) housings. Composite housings offer excellent explosion-proof performance and superior pollution resistance.
Internal Core: Composed of zinc oxide valve stacks, insulation supports, and pressure springs to ensure tight electrical contact.
Sealing System: Usually employs a double-layer seal filled with high-purity nitrogen to prevent oxidation and moisture contamination.

3.Detailed Elaboration on Conventional Electrical Preventive Tests

3.1 Insulation Resistance Measurement

Measured using a 2500 V or 5000 V insulation resistance meter. For arresters rated 35 kV and below, the insulation resistance should typically not be less than 1000 M $Ω$ . For 110 kV and above, it should not be less than 2500 M $Ω$ .

3.2 DC Reference Voltage $U_{1 mA}$ :

U_1 mA=f(I=1 mA)

Description:
This value is the most critical preventive test item. It measures the DC voltage required to cause a 1 mA current flow through the arrester. The measured value should be compared with the factory test report; a deviation exceeding $\pm 5%$ indicates potential valve degradation or uneven potential distribution.

3.3 Leakage Current at 75% $U_{1 mA}$ :

I_0.75≤50 μA

Description:
Measurement of leakage current at 0.75 times the DC reference voltage. Typically, the current should not exceed 50 $μ$ A. A significantly higher value indicates moisture ingress due to seal failure or severe surface contamination.

3.4 Technical Data and Diagnostic Comparison Table

Test Item	Pass Standard (110 kV MOA)	Typical Failure Manifestation	Diagnostic Recommendation
Insulation Resistance	$\geq 2500$ M $Ω$	Drops exponentially to 500 M $Ω$	Internal moisture or external flashover
$U_{1 mA}$ Voltage	$\geq 145$ kV (Ref. value)	Decrease exceeds $5%$	Valve aging or material degradation
75% $U_{1 mA}$ Current	$\leq 50$ $μ$ A	Increases beyond 200 $μ$ A	Seal failure, moisture ingress

4.Operational Guide for Field Preventive Testing and Application

4.1 Field Testing Execution Steps

Preparation: Thoroughly clean the arrester surface to eliminate the impact of surface leakage current on the measurement results.
Wiring: High-voltage leads should be as short as possible with sufficient clearance, and the bottom terminal must be reliably grounded.
Testing: Gradually increase the voltage until the current reaches 1 mA and record the voltage; then decrease to the 75% point to record the leakage current.
Discharging: After the test, the arrester must be fully discharged using a dedicated discharge rod.

4.2 Critical Precautions

Guard Ring Application: When testing $U_{1 mA}$ in high-humidity environments, a guard ring should be applied to the porcelain surface and grounded to eliminate the influence of surface current on the valve data.
Temperature Correction: While $U_{1 mA}$ is less affected by temperature, the resistive current is highly sensitive. Data recorded at ambient temperatures above 30 degrees Celsius should be converted for proper comparison.

4.3 Application Scenarios and Expected Outcomes

Scope: Applicable to annual spring inspections, handover tests after equipment overhaul, and special patrols before and after the lightning season.
Expected Results: By strictly following these testing standards, the failure rate of surge arresters can be reduced by more than 80%. This approach can accurately intercept over 95% of "faulty" equipment in the early stages of moisture ingress or aging, significantly enhancing the service life and security of 110 kV and above grid assets.

Give a tip and encourage the author!

Topics:

Surge Arrester

MOA Structure

Overvoltage Protection

Comments

Share your question or perspective

Surge Arrester Structure and Electrical Testing Technology

Comments

Related Knowledge