Surge Arresters: Factory Acceptance Testing Procedure

Factory Acceptance Testing (FAT) is an essential phase in the manufacturing and quality assurance process for surge arresters. 

This procedure explains the systematic method for conducting FAT that encompassing 

1). Visual inspections, 

2). Mechanical checks and 

3). Routine electrical tests 

in accordance with the recognized international standards such as IEC 60099-4 and IEEE C62.11.

The primary objective of FAT is to verify that manufactured surge arresters that meet all technical specifications, performance requirements and safety standards prior to shipment. 

By implementing FAT procedure manufacturers and utilities can identify and also rectify potential defects (faults) early in the supply chain reducing the risk of field failures and ensuring reliable protection of the electrical equipment throughout the their operational life.

This post provides a comprehensive framework for conducting FAT procedure on surge arresters including standardized test procedures.

Standards 

The testing and acceptance of surge arresters are primarily governed by international recognized standards that establishes the minimum performance requirements and testing methodologies:

1). IEC 60099-4 

2). IEEE C62.11 

This ensures a common understanding of acceptance criteria and prevents disputes (variations) regarding the test results interpretation.

FAT Preparation 

The successful execution of the FAT test requires thorough preparation and coordination among the manufacturer, utility representative and testing personnel. 

The following preparation steps should be completed before any testing commences.

Equipment Calibration & Traceability

All test equipment must be used during FAT for calibration in accordance with the recognized standards and traceable to standards laboratories. 

Test Plan Review

The manufacturers FAT test procedure should be reviewed and approved prior to testing. 

The procedure should clearly identify which tests will be performed, the sequence of testing, acceptance criteria for each test and the data recording procedures. 

Any deviations from standard test procedures must be clearly documented and justified.

Test Equipment Verification

Before starting the testing procedure all test equipment must be verified to confirm the proper operation and calibration status. 

High-voltage test equipment should be verified for proper grounding, interlocks and safety features.

Factory Acceptance Testing Procedures

Visual Inspection

The FAT procedure starts with a initial visual inspection and dimensional verification of each surge arrester unit.

Nameplate Verification

Confirm that the nameplate markings are clearly visible that accurately reflect the design specifications and match the (PO) purchase order. 

Verify that the following information is present & correct:

1). Arrester type & rating,

2). Voltage class and system voltage,

3). Nominal discharge current (In),

4). Maximum continuous operating voltage (MCOV),

5). Energy absorption capability and

6). Manufacturing date & serial number and

7). Manufacturer identification

Mechanical Inspection

Visually inspect all external surfaces for defects, damage (or) manufacturing anomalies. 

Verify that the arrester porcelain (or) composite housing for cracks, chips, surface contamination (or) material irregularities. 

Verify that all mechanical connections, terminals, and mounting hardware are present and properly secured. 

Check for proper fit of all components and confirm that no foreign material (or) manufacturing debris remains inside (or) on the arrester.

Dimensional Verification

Measure the important dimensions (parameters) including 

• Overall height of surge arrester, 
• Flange diameter and 
• Terminal spacing 

to confirm conformance to the manufacturer drawings.

Cross check physical attributes against the specifications which is provided in the purchase order & standard datasheets.

Cleanliness Assessment

Verify that the arrester is 

• Clean and free of dust, 
• Oil (or) other contamination,

that could affect electrical performance or reliability. 

This is particularly important for the composite insulators where the contaminants may degrade (or) decrease surface resistance.

Electrical Testing

Following the successful visual and mechanical inspection of the surge arresters proceed to electrical testing which verifies their electrical performance characteristics:

Insulation Resistance Testing (IR)

Insulation resistance (IR) testing measures the resistive path across the surge arresters terminals and ground which indicating the integrity of the complete insulation system.

Test Voltage

Typically 500 VDC (or) 1000 VDC (per manufacturer specification)

Test Duration

Minimum 60 seconds.

Measurement taken at 60 seconds.

Acceptance Criterion

Insulation resistance should exceed minimum values specified in the standard and manufacturers data sheet (typically >1000 MΩ for most arresters)

Procedure

1). Connect the megohmmeter (MΩ) between the arrester terminals and ground.

2). Record the insulation resistance (IR) value. 

3). Any significant deviation from expected values may indicate moisture ingress or manufacturing defects.

4). A low insulation resistance reading may necessitate further investigation (or) rejection of the unit. 

5). In some cases controlled drying procedures may be employed to restore acceptable IR values but such corrective actions should be documented.

AC Withstand Voltage Test

The AC withstand voltage test verifies that the surge arresters insulation can withstand elevated AC voltages without breakdown (or) excessive leakage current

Test Voltage

125% of the arrester’s rated voltage (eg: 1.25 x Rated Voltage)

Test Duration

Typically 1 minute at full voltage

Acceptance Criterion 

No flashover or breakdown should occur.

Leakage current should remain within specified limits.

Procedure

1). Apply AC voltage to the arrester terminals with respect to ground gradually increasing voltage to the test level. 

2). Monitor for any signs of electrical discharge (or) abnormal current.

3). Record the leakage current & any observations of the arrester functionality.

4). This test also validates that the arrester insulation system which provides an adequate margin above normal operating voltages and can withstand expected over voltages without failure.

Impulse Testing to Specified BIL

Impulse testing verifies the arresters ability to withstand and protective characteristics against lightning and switching surges

Test Impulse

Standard 1.2/50 microsecond impulse waveform (8/20 microsecond current impulse)

Test Voltage

Adjusted to produce a discharge current equal to the specified impulse rating (typically 5 kA, 10 kA or 20 kA for most arresters)

Acceptance Criterion

Measured voltage during impulse discharge must not exceed the protective level specified in the manufacturer data and applicable standard

Procedure

1). Apply impulse voltage to the arrester via standardized impulse generator equipment. 

2). Capture the voltage and current waveforms and measure the peak voltage (V_P) developed across the surge arrester during the impulse discharge. 

3). Verify that measured values that comply with the manufacturers protective level specifications.

4). Impulse testing typically includes multiple impulses at the specified current level to demonstrate consistent protective characteristics. 

5). The voltage recorded during the first impulse is often the importance acceptance criterion.

Data Logging & Documentation

All FAT test data must be meticulously recorded in the factory quality records with complete traceability

Test Report Contents

The FAT report should include 

• Identification of the arrester (serial number, type, rating) 
• Date and time of testing, 
• Identification of the test equipment used (including calibration status), 
• Name and signature of the test technician and 
• Results of all tests performed. 

Each test result should clearly indicate whether the unit passed (or) failed the acceptance criteria.

Raw Data & Waveforms

For electrical tests particularly 

• Impulse testing, 
• Oscilloscope waveforms and 
• Calculated parameters 

should be retained as part of the quality record. 

These provide documentary evidence of test performance and can be useful for investigating any subsequent questions regarding test validity.

Traceability Matrix

The FAT report should reference the applicable standards, manufacturer specifications and purchase order requirements creating a clear traceability between the test results and the acceptance criteria.

Acceptance Criteria 

Surge arresters must meet all applicable acceptance criteria to be approved for shipment. 

Typical acceptance criteria are summarized as follows:

Test	Acceptance Criterion
Nameplate/Dimensions	Match specifications exactly
Visual Inspection	No defects, damage (or) contamination
Insulation Resistance	≥ manufacturer minimum (typically >1000 MΩ)
AC Withstand (125% rated voltage)	No flashover; leakage current within limits
Impulse Test (to specified BIL)	Protective voltage ≤ manufacturer specification

Any arrester that fails to meet a test criterion must be addressed through one of the following actions:

1). In some cases, arresters failing IR testing due to moisture may be dried and retested. Rework procedures must be approved and documented.

2). Units that cannot be brought into compliance through rework (or) that fail electrical performance tests must be rejected and segregated from acceptable units. Rejection must be documented and the utility witness should be notified.

3). In rare conditions where the test results are marginal (or) queries exist regarding the acceptance criteria applicability & an engineering review may be guaranteed. This must involves both the manufacturer and the utility’s engineering team.

On-Site Commissioning & Pre-Energization Testing

Although FAT provides assurance of arrester quality at the factory commissioning procedures and pre-energization testing at the installation site serve as a final verification that units have not been damaged during transportation (or) storage.

Visual Inspection

Upon receiving surge arresters should be visually inspected for damage sustained during shipping. Any units showing evidence of damage (or) physical alteration should be quarantined and investigated.

Insulation Resistance Retest

IR testing is commonly repeated on-site prior to energization to confirm that no moisture ingress (or) degradation has occurred during transit (or) storage. 

IR values must be comparable to factory (FAT) test results.

Significant decreases may use to warrant further analysis and testing.

Documentation 

Prior to installation the complete FAT report including all test records and certifications must be reviewed to confirm that the surge arrester was properly tested and accepted at the factory.

Summary

Factory Acceptance Testing (FAT) of surge arresters ensures that the compliance with IEC/IEEE standards through visual, dimensional and electrical tests before proceed to dispatch. 

Detailed testing, documentation and defined acceptance criteria provide assurance of quality, reliability & safety reducing field failures & supporting long-term performance in power systems.