High-voltage electrical testing is indispensable in power systems, but the risks it poses are equally formidable. Without rigorous precautions, testing activities can jeopardize both human life and equipment integrity. This guide outlines the essential safety regulations for high-voltage measurements, focusing on the use of instrument transformers, clamp-on ammeters, insulation resistance testers, and ground resistance testers.

Regulations for Using Instrument Transformers in High-Voltage Measurements

Instrument transformers, such as current transformers (CTs) and voltage transformers (VTs), are vital for safe and accurate high-voltage measurements. Strict safety rules apply when they are used in live circuits.

• Team Operation Requirement: At least two qualified personnel must be present, and a group operation ticket must be filled before beginning.

• Current Transformer Connections: All connections and disconnections must only be performed after the high-voltage circuit is de-energized. Conductor size must match the expected current load.

• Voltage Transformer Connections: Voltage measurement wiring may be done under live conditions but must comply with live work regulations. Wires must be short, joint-free, and securely fastened.

• Measurement on Low-Voltage Side: All readings should be taken from the transformer’s low-voltage side for operator safety.

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• Protective Equipment: Insulated gloves, safety goggles, insulating boots (outdoors), and an insulating platform must be used during operations.

• Instrument Safety: Non-metallic instrument casings must be insulated from ground, while metallic casings must be properly grounded.

• Work Area Control: Rope barriers or fencing must be installed around the testing zone to prevent unauthorized access.

Regulations for Using Clamp-On Ammeters in High-Voltage Testing

Clamp-on ammeters provide a non-intrusive method for measuring current, but high-voltage environments demand special caution.

• No Auxiliary Connections: It is forbidden to connect additional instruments via wires from the clamp-on ammeter.

• Cable Spacing Requirement: For high-voltage cable testing, phase conductors must be at least 300 mm apart and well insulated. If one phase is grounded, testing is prohibited.

• Bare Conductor Measurements: Operators must maintain safe clearances and wear insulated gloves and insulating boots.

• Fixed Measurement Range: The measurement range must not be altered during testing.

• Instrument Cleanliness: The clamp meter must be cleaned before use to ensure reliable insulation performance.

Regulations for Using Insulation Resistance Testers

Insulation resistance testing reveals the condition of electrical equipment insulation. However, performing this test on high-voltage systems requires strict procedural discipline.

• Team Operation Requirement: A minimum of two people is mandatory, with an operation ticket completed in advance.

• De-energization First: The equipment under test must be de-energized, verified, and discharged before measurement.

• Personnel Safety: No one should be on the equipment. Staff at both ends of cables or lines must be notified before testing.

• Circuit Isolation: For circuits sharing the same support or running parallel, all must be de-energized to prevent induced voltages.

• Cable and Capacitor Testing: Cables, capacitors, and long overhead lines must be fully discharged before testing. Disconnect the tester’s lead before stopping the crank to prevent equipment damage.

• Work Near Live Equipment: Maintain safe distances, assign a safety observer, and position the tester properly.

• Ground Connection: Testers with grounding terminals must be grounded before use.

• Weather Restrictions: Outdoor insulation resistance testing must not be conducted during thunderstorms.

• Lead Integrity: All measurement leads must have intact insulation and must not be short-circuited.

Regulations for Using Ground Resistance Testers

Ground resistance measurement follows similar rules to insulation resistance testing, with a few critical points of distinction.

• Disconnect Ground Lead: The grounding conductor must be disconnected before testing.

• Closed Measurement Circuit: While cranking the tester, its measurement terminals must never remain open.

Conclusion

Safe high-voltage measurement is a non-negotiable practice in the electrical industry. From using instrument transformers and clamp-on ammeters to operating insulation and ground resistance testers, every step must comply with established safety protocols. By respecting these detailed guidelines, electrical professionals not only prevent accidents but also ensure reliable, long-term operation of critical power infrastructure.