Choosing the Right Ultra-Low Frequency AC High-Voltage Tester Based on IEC/IEEE Standards

When selecting an Ultra-Low Frequency AC High-Voltage Tester, the voltage rating and application should be based on the equipment being tested and its insulation class. The IEC (International Electrotechnical Commission) and IEEE (Institute of Electrical and Electronics Engineers) standards provide guidelines for high-voltage testing of electrical equipment, including the selection of the right test voltage for ultra-low frequency (typically between 0.1 Hz to 1 Hz) testing.

These standards are critical for ensuring the insulation strength of electrical equipment, including transformers, cables, generators, switchgear, and GIS systems. Ultra-low frequency AC testing is often performed to simulate long-term operating conditions and ensure that the equipment will not experience insulation breakdown or failure under normal operating conditions.

IEC and IEEE Guidelines for Ultra-Low Frequency AC Testing

IEC 60060-1: High Voltage Test Techniques – Part 1: General Definitions and Test Requirements

According to IEC 60060-1, high-voltage AC testing is typically performed on electrical equipment based on the equipment’s rated voltage. Ultra-low frequency AC testing is conducted with specific voltage levels depending on the rated voltage of the equipment being tested.

• Testing voltage for equipment rated ≤ 1 kV (Low Voltage):
  • Typically, low voltage systems are tested at 1.5 times the rated voltage, so for a 1 kV system, a testing voltage of 1.5 kV to 2 kV is used.
• Testing voltage for equipment rated 1 kV to 36 kV (Medium Voltage):
  • For medium-voltage systems (e.g., transformers and cables rated for 11 kV, 20 kV, etc.), the testing voltage is typically 2 times the rated voltage.
  • For example, a system rated at 11 kV will be tested at 22 kV, and 20 kV systems will be tested at 40 kV.
• Testing voltage for equipment rated > 36 kV (High Voltage):
  • High-voltage equipment, such as GIS (Gas Insulated Switchgear) or large transformers, is tested at 2 to 2.5 times the rated voltage, sometimes higher for special tests.
  • For example, 110 kV systems will typically be tested at 220 kV or 250 kV, and 220 kV systems may be tested at 450 kV.

IEEE C57.12.90: Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers

IEEE C57.12.90, which covers the high-voltage testing of transformers, specifies the testing voltages based on the transformer’s rated voltage:

• For distribution transformers rated up to 36 kV: The high-voltage withstand test is typically performed at 1.5 times the rated voltage.
• For power transformers rated above 36 kV: These are usually tested at 2 times the rated voltage (or higher, depending on the application), as defined in the IEEE standard.

IEC 62271-203: High Voltage Switchgear and Controlgear – Gas-Insulated Switchgear

IEC 62271-203 applies to GIS (Gas Insulated Switchgear) and similar equipment, which typically requires ultra-low frequency AC testing to ensure insulation strength. This standard provides a testing voltage range that is 2 to 2.5 times the equipment’s rated voltage for high-voltage systems:

• GIS systems rated for 72.5 kV to 245 kV will typically be tested at 2.5 times the rated voltage (e.g., a GIS rated for 145 kV may require a test voltage of 362.5 kV).

Voltage Selection Guidelines Based on Equipment Rating

Application Breakdown Based on Standards

Low-Voltage Systems (up to 1 kV)

• Voltage: 1.5 times the rated voltage.
• Typical Equipment: Low-voltage distribution panels, low-voltage cables, small transformers.
• Example: For an 800 V transformer, the testing voltage would be around 1.2 kV to 1.6 kV.

Medium-Voltage Systems (1 kV to 36 kV)

• Voltage: 2 times the rated voltage.
• Typical Equipment: Medium-voltage cables, transformers, switchgear.
• Example: A 20 kV rated transformer would be tested at 40 kV, and a 33 kV cable would be tested at 66 kV.

High-Voltage Systems (Above 36 kV to 72.5 kV)

• Voltage: 2 to 2.5 times the rated voltage.
• Typical Equipment: High-voltage cables, transformers, GIS, and HV switchgear.
• Example: A 110 kV rated transformer or switchgear would typically be tested at 220 kV.

Very High-Voltage Systems (Above 72.5 kV)

• Voltage: 2.5 to 3 times the rated voltage.
• Typical Equipment: Very high-voltage transmission lines, GIS, large transformers, and substation equipment.
• Example: For a 220 kV transmission system, the test voltage may go up to 660 kV, as per standards.

Conclusion

Selecting the correct test voltage for ultra-low frequency AC testing of electrical equipment should be based on the rated voltage of the equipment being tested, as well as the guidelines set forth by IEC and IEEE standards. These standards ensure that testing is done with appropriate voltage levels to simulate long-term operating conditions and stress the insulation, without risking damage to the equipment or the test system.

Always ensure to verify the rated voltage of the equipment, match it with the required test voltage, and apply the test voltage per the relevant IEC/IEEE standards for safe and effective testing.