What should be noted when selecting and installing GIS voltage transformers?

• Voltage Level: It must be consistent with the voltage level of the GIS system. For example, 110kV and 220kV GIS systems require voltage transformers of corresponding levels to ensure accurate voltage measurement and long-term stable operation of the equipment.
• Rated Capacity: Select based on the power requirements of devices connected to the secondary circuit (such as measuring instruments and protection devices). If there are many connected devices with high power, a transformer with a larger capacity should be chosen to avoid affecting measurement accuracy or damaging equipment due to insufficient capacity.
• Accuracy Class: Determine according to the purpose. For metering, higher accuracy classes are required, usually 0.2 or 0.5; for relay protection, 3P or 6P is sufficient.

(2) Paying Attention to Insulation Performance

• Insulation Type: Voltage transformers in GIS commonly use SF₆ gas insulation or epoxy resin casting insulation. SF₆ gas insulation has good insulation and arc-extinguishing effects, while epoxy resin casting insulation has a compact structure and high reliability. The choice can be made according to the actual operating environment and needs.
• Insulation Level: It must withstand the maximum operating voltage, lightning overvoltage, and operating overvoltage of the system. The higher the voltage level, the stricter the requirements for insulation level, which is directly related to the safe operation of the equipment.

• Cleanliness: The interior of the GIS must be clean, without dust, metal debris, or other impurities, which may affect the insulation performance of the voltage transformer and even cause discharge faults. Before installation, the GIS air chamber should be thoroughly cleaned and inspected.
• Sealing: The sealing of the GIS air chamber is important to prevent SF₆ gas leakage. SF₆ is the key medium for insulation and arc extinguishing in GIS equipment, and leakage will reduce insulation performance and affect the operation of the voltage transformer.
• Temperature and Humidity: The temperature and humidity of the installation environment should meet product requirements, generally in a dry and moderately temperatured place. Excessive humidity may cause insulation to get damp and affect equipment performance.

(2) Standardizing the Installation Process

• Hoisting and Handling: When handling and hoisting the voltage transformer, use appropriate lifting tools and operate according to the designated lifting points of the product to prevent collision, tilting, or excessive vibration, which may damage the internal structure.
• Electrical Connection: The wiring of the secondary circuit should be correct and firm, and the connecting wires should have sufficient cross-section and insulation performance to prevent poor contact and short circuits. For the primary side connection, ensure tight connection, good conductivity, and meet current-carrying requirements.
• Grounding Requirements: The secondary windings and shell of the voltage transformer should be reliably grounded to ensure the safety of equipment and personnel. The grounding resistance should meet relevant standards, generally not exceeding 4 ohms.

(3) Conducting Post-Installation Debugging

• Insulation Testing: After installation, conduct insulation resistance testing and withstand voltage testing on the voltage transformer to check whether its insulation performance meets the requirements.
• Transformation Ratio and Polarity Check: Test whether the transformation ratio meets the design value to ensure measurement accuracy; check whether the polarity is correct to avoid incorrect instrument indication or misoperation of protection devices.
• Gas Detection (for SF₆ Insulation Type): For those using SF₆ insulation, detect the gas pressure and micro-water content in the air chamber to ensure they are within the normal range.