1. Introduction to GIS Technology GIS optimizes the design of all primary equipment in a substation, except for the transformer, into an organic whole, generally in the form of building blocks. In general, it consists of eight major components: circuit breaker (CB), disconnector (DS), grounding switch (ES), voltage transformer (VT), current transformer (CT), surge arrester (LA), busbar (BUS), and bushing (BSG). GIS has the following characteristics: (1) Miniaturized structure: It uses high-performance gas as insulation and arc extinguishing medium, which greatly reduces the volume of the substation and realizes the miniaturization of the substation. (2) High reliability: All live parts are sealed in inert gas SF6, which isolates them from external influences such as salt spray, dust, and snow, greatly improving the reliability of operation. In addition, it has excellent earthquake resistance. (3) Good safety: The live parts are sealed in a grounded metal shell, so there is no risk of electric shock; SF6 gas is an inert gas, so there is no risk of fire. (4) Eliminates adverse external influences: Because the live parts are fully enclosed in a metal casing, electromagnetic and static electricity are shielded, and there will be no noise or radio interference. (5) Short installation cycle: Due to the miniaturized structure, the whole machine can be assembled at the manufacturing plant. After passing the test, it can be transported to the site in the form of units or whole bays, thus shortening the on-site installation period. (6) Convenient maintenance and long maintenance cycle: Due to the reasonable structural layout and advanced arc extinguishing system, the maintenance cycle is extended and the service life of the product is improved. In addition, due to its miniaturized structure and the close installation position to the ground, maintenance is more convenient. The technical characteristics of outdoor open-type power distribution equipment and GIS scheme are compared in Table 1. [img=300,229]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hbdljs/2001-10/44-1.jpg[/img] 2 220 kV GIS Installation 2. Preparations before installation (1) Site cleanup: Ensure the ground and trenches are thoroughly cleaned. (2) According to the foundation drawing and overall layout drawing of the GIS equipment, use an ink line to draw the spacing, distance between bays, and center lines between main busbars on the ground for GIS equipment installation. (3) Along each center line, use a theodolite to measure 2-4 elevation points at each bay and record them as the basis for GIS placement. (4) After the GIS is transported into the factory, install it according to the plan and procedures; do not pile it up. (5) Familiarize yourself with the GIS equipment drawings and operating procedures. 2.2 GIS Installation Guidelines (1) First, confirm the installation benchmark and the first unit to be installed. If the selection is inappropriate, it will directly affect the subsequent installation work. (2) Generally, install the main busbar first, using the main busbar in the middle interval as the benchmark. When the main busbar is in place, it should be slightly raised to ensure that the benchmark surface under the busbar frame is 2-5 mm higher than the elevation measured on the GIS plant floor. (3) Using the benchmark main busbar as the center, connect the other interval main busbars in sequence at both ends until the installation is complete. (4) Use a theodolite to measure the elevation of all main busbars to check the installation quality. It is required that the interfaces on each main busbar are kept on the same horizontal plane; otherwise, use shims for adjustment. (5) After the main busbars are adjusted, according to the requirements of the GIS overall layout drawing, install the incoming and outgoing line bays and bus coupler bays respectively, using the main busbars as the benchmark. The order is: inside first, then outside. (6) When assembling, the polarity of the CT should be checked first (Note: Do not reverse it). (7) In order to arrange the work reasonably and shorten the construction period, various operations can be carried out in a cross manner (Note: The first gas chamber should only be filled with gas after more than two gas chambers have been assembled). (8) On-site testing can only be carried out after all the assembly and SF6 gas filling are completed (Note: The main circuit resistance should not be measured after the GIS is evacuated and before filling with SF6 gas, because the product is in a sub-vacuum state at this time, and the insulation performance is extremely poor. During the test, the basin insulator may be damaged due to surface discharge). (9) After the test, in addition to replenishing the SF6 pressure of each gas chamber to the rated gauge pressure, each SF6 gas density relay, pressure switch, safety valve, etc. should also be set to the rated position. (10) Final inspection and handover report. 2.3 Installation Precautions (1) Do not hit the bushings, pipelines, boxes, etc. or apply extra force. (2) Avoid working in the rain when installing outdoors. (3) Exercise extreme care during installation to prevent dust and moisture from entering the GIS. (4) Prevent impurities from entering the GIS; cover the flange holes with plastic sleeves before installation. (5) Protect the inflation port from damage or contamination. (6) When placing the O-ring, do not damage it. Apply sealant (white) to the side of the O-ring closest to the atmosphere and its corresponding flange sealing surface. (7) Do not remove the covers from the tank and pipelines before installation. (8) Before vacuuming, quickly place the desiccant to minimize its exposure time to the atmosphere (generally not exceeding 8 hours). (9) Tighten the bolts with appropriate torque. 3 Key Points for On-site Commissioning After the GIS is installed, it must undergo rigorous inspection and testing to confirm that the installation is correct and reliable before it can be put into operation. Specific items and methods are as follows: 3.1 Visual Inspection: Main contents include: assembly status, looseness of parts, grounding terminal configuration, and whether there is damage to gas pipelines and cable trays. The above inspection should be carried out according to the installation inspection card. 3.2 Secondary Wiring Inspection: Inspect the wiring from the control panel to the operating mechanisms of components such as circuit breakers and disconnect switches, and inspect the wiring from the control panel to the terminal boxes of components such as CTs and CVTs. Also check the tightness of the terminals and the condition of the terminal markings. 3.3 Insulation Resistance Measurement (including main circuit and secondary circuit): Use a 1000V megohmmeter to measure the insulation resistance of the main circuit (busbars, circuit breakers, disconnect switches, and grounding switches, etc.) to ground, and the control circuit to ground. The insulation resistance value of the main circuit can be measured directly from the conductive rod of the GIS outgoing bushing. Measure the insulation resistance value of each wire on the terminal block. Judgment criteria: Main circuit above 1000 MΩ, control circuit above 1 MΩ. 3.4 Main Circuit Resistance Measurement To facilitate comparison with the manufacturer's measurement results, the same measurement circuit and measurement method should be used for both. The following procedure is limited to the field: (1) Close the isolating switch, circuit breaker and grounding switch of the circuit to be tested. (2) After removing the grounding plate from the grounding switch, connect the power supply. (3) Apply DC 20-100 A and measure the millivolts across the grounding switch (in this case, the millivoltmeter measurement point should be as far away from the measuring power supply as possible). (4) Compare the field measurement value with the manufacturer's measurement value. Judgment criterion: The field measurement value should not exceed 20% of the manufacturer's measurement value. 3.5 Switch Operation Test and Interlocking Test (1) Opening and Closing Test Under the rated operating pressure and specified control voltage, press the button on the control panel to check the opening and closing status. (2) Continuous Opening and Closing Operation Test Except for the grounding switch which is manually controlled, 5 to 10 continuous opening and closing operations should be performed under the rated operating pressure and rated control voltage. During this process, check the operating mechanism, changeover switch, etc. （3） Operate each component and check the interlocking between the circuit breaker and the disconnector. Judgment criteria: The interlocking conditions specified in the electrical control schematic diagram must be met. 3.6 Measurement of SF₆ gas moisture content in each chamber The moisture content in the circuit breaker chamber should be less than 150×10⁻⁶ (volume fraction), and the moisture content in other chambers should be less than 250×10⁻⁶ (volume fraction). 3.7 Compressed air system leakage test After the circuit breaker gas tank is filled to the rated pressure (1.47×10⁶Pa), close the gas supply valve and maintain it for 12 h or 24 h, checking the pressure drop rate (required drop rate: less than 5% in 12 h; less than 10% in 24 h). 3.8 SF6 Gas Leakage Detection At the assembly site, seal the flange connection on the casing with plastic film (the equipment under test must be filled with gas and left to stand for more than 3 hours). Use an SF6 leak detector to measure the SF6 content in the containment area (the unit of measurement for the leak detector is 10⁻⁶, volume fraction). The annual leakage rate must be less than 1%. 3.9 SF6 Density Relay and Air Pressure Switch Test (1) Temperature Compensation Pressure Switch Check that the operating value of the temperature compensation pressure switch in the SF6 gas monitoring box is within the set range. (2) Air Pressure Switch Control the inlet valve and outlet valve on the air tank, adjust the air pressure, and check the operating pressure of the air pressure switch installed in the circuit breaker operating mechanism box. 3.10 CT Test Measure the insulation resistance of the secondary coil to ground on the terminal block with a 500 V megohmmeter. The value should be greater than 1 MΩ. 3.11 CVT Test (1) Measure the insulation resistance of the secondary coil to ground on the terminal block. The value should be greater than 5×103 MΩ. (2) Apply power frequency voltage to the secondary winding and the grounding terminal of the primary winding. Judgment criterion: withstand power frequency test voltage of 2 kV for 1 min. (3) If conditions permit, a power frequency withstand voltage test can be performed on the primary winding, but the test voltage shall not exceed 1.3 times the rated voltage. 3.12 LA Test After LA is installed, leakage current should be measured in clear weather without switching operation. Check and record the initial data of the discharge counter. Judgment criterion: if the resistive current exceeds 0.5 mA, the cause must be checked and analyzed in detail. 3.13 Main Circuit Power Frequency 1 min Withstand Voltage Test To prevent installation errors and ensure the safe operation of GIS, after the equipment is installed, the main circuit (to ground and between the break points) should undergo a power frequency voltage test. The withstand test voltage is 0.8×460 kV for 1 min. 3.14 Secondary Circuit Power Frequency 2 kV 1 min Withstand Voltage Test The control circuit and auxiliary circuit should undergo a power frequency voltage test to ground, with a withstand voltage of 2 kV for 1 min. 4. Issues to Note During installation, all equipment inside the GIS room should be clean, and the installation site environment should also be clean. The standby power supply for the first phase of a power plant is provided by a 220 kV system. The 220 kV distribution equipment is a GIS manufactured by Xi'an High Voltage Switchgear Factory using technology imported from Mitsubishi Corporation of Japan. This GIS system has 7 bays: 3 incoming line bays; 2 outgoing line bays; 1 bus tie bay; and 1 CVT bay. During installation, due to inadequate sealing of the entrances and exits of the GIS room, coupled with the nearby construction site resulting in significant dust, the GIS room's hygiene was poor. The planned construction period was 3 months, but due to the above reasons, the construction period was delayed by 3 months, causing significant losses to the project. Later, during the construction of the 500 kV GIS power distribution equipment for this project, the experience gained from the construction and installation of the 220 kV GIS was incorporated, and various measures were taken to ensure the cleanliness of the indoor environment of the 500 kV GIS, enabling the project to be completed two months ahead of schedule.