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Excerpt from **Power Grid Company’s Regulations on Substation Inspection and Testing 1 Inspection Conditions 1.1 Environmental Requirements Unless otherwise specified, inspections shall be carried out under favorable atmospheric conditions, and the atmospheric conditions should remain relatively stable during the inspection period. a) The detection temperature should not be lower than 5°C ； b) The relative environmental humidity should not exceed 80%; if testing is to be carried out outdoors, it should not be done in conditions of thunder, rain, fog, or snow ； 1.2 Requirements for the device under test: a) The device under test must be in operation ； b) The location of the grounding point meets the safety distance requirements for live working by test personnel; test personnel should be able to reach the test site easily to carry out inspections. 1.3 Personnel Requirements: Personnel conducting live detection of the grounding current in the outer sheath of high-voltage cables should meet the following criteria: a) They should have knowledge of the structural characteristics, operating principles, operational status of high-voltage cable equipment (such as cable joints and terminations), as well as the basic factors that can lead to equipment failures ； b) Be familiar with the basic principles of grounding current detection for cable outer shields ； c) Understand the working principle, technical parameters, and performance of clamp ammeters, and master their operation methods ； d) Possess certain on-site work experience, and be familiar with as well as able to strictly comply with the relevant safety management regulations for power production and work sites. e) Have completed induction training and passed the examination. 1.4 Safety requirements a) The relevant requirements of the **Power Grid Company’s ‘Safety Procedures for Electrical Work (Substation Section)’ must be strictly followed** ； b) The live inspection work must be carried out by at least two persons. The person in charge of the testing should be an experienced individual; before starting the testing, this person must provide all testers with detailed instructions regarding safety precautions ； c) It should be carried out in good weather; this work must not be performed in case of thunder, rain, snow, or fog. It is also not advisable to carry out this work when the wind speed is above level 5 ； d) When performing inspections, maintain a sufficient safety distance from the live parts of the equipment, and wear insulating gloves and insulating shoes. e) When conducting tests, prevent accidental contact with or operation of the equipment. 1.5 Instrument requirements: For the live detection of the grounding current in the outer shielding layer of high-voltage cables, a clamp ammeter is generally used. 1.5.1 Main technical specifications a) Detection current range: 0A~500A. b) Resolution: not greater than 0.2A. 1.5.2 Functional requirements a) The clamp ammeter should be easy to carry and operate, offer high measurement accuracy, and provide good repeatability of measurement results ； b) It should have multiple range AC current scales ； c) The opening diameter of the jaws of the clamp ammeter should be larger than the diameter of the grounding wire. 2 Preparation for testing a) Before testing, it is necessary to obtain information such as the model and manufacturer of the equipment under test, as well as the date of installation. It is also important to understand the operating conditions of the equipment, any historical defects, and any familial defects, in order to develop appropriate technical measures. b) Provide drawings consistent with the inspection work, records of the previous inspection, and standard operating cards. c) Obtain the historical test data of the tested equipment ； d) Check that the environment, personnel, instruments, and equipment meet the testing requirements. e) Complete the work permit procedures in accordance with relevant safety production management regulations. 3 Test Methods 3.1 Test Principle The grounding method for single-core high-voltage cable lines is either single-end grounding or cross-interconnected grounding; under normal conditions, the grounding current on the metal sheath is zero or very small. When the outer shielding layer of a single-core high-voltage cable line ages or is damaged, there will be a significant change in the grounding current in the metal sheath. By measuring the grounding current of the metal sheath in single-core high-voltage cable circuits, the health condition of the outer sheath of the cable circuits can be reflected in a timely manner. 3.2 Testing Procedure a) Before testing, set the clamp ammeter to the correct range, adjusting it from the highest value to the lowest, in order to measure the ground current ； b) Record the load current. c) Keep proper records of the measurement data. 3.3 Inspection and acceptance: Check whether the inspection data is accurate and complete. 4 Analysis and processing of test data a) Taking into account the load conditions of the cable line, compare the test results with the requirements specified in the following test standards: Grounding current of the outer sheath of rubber and plastic-insulated power cables: