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Abstract: This paper is discussing about the installation procedure, test procedure and construction technology of the outdoor 220kV HV SF6 gas-insulated metal-enclosed switchgear, type: ZF1-20, which is manufactured by Xi’an HV Electric Institute Co., Ltd. of Shanghai Branch, and installed successfully for the first time in Gaoqiao substation, Ningxia province.

SF6 gas-insulated metal-enclosed switchgear, called GIS for short, is a complete set of equipment in different kinds of structure and arrangement that the HV electrical apparatus (that the energized conductor is enclosed in the grounded metal shell) is assembled as per main wiring connection requirements of different substations. And some SF6 is filled into the HV electrical apparatus as medium of insulation and arc extinguishing. This kind of product only occupies small floor space with high safety and reliability, little maintenance but a long period of non-overhaul. Moreover, its environmental suitability is excellent without fire hazard etc. This paper is discussing about the installation procedure, test procedure and construction technology of the outdoor 220kV HV SF6 gas-insulated metal-enclosed switchgear, type: ZF1-220, which is manufactured by Xi’an HV Electric Institute Co., Ltd. of Shanghai Branch, and installed successfully for the first time in Gaoqiao substation, Ningxia province.

GIS HV combined electrical apparatus, of which the major elements except transformer in a substation are made into a typical unit structure, could be assembled into a complete set according to the user’s main wiring connection requirements. Between the elements, the conductor connection is adopted for the internal and flange connection for the external shell with an O-ring for sealing. All of HV energized parts are enclosed in the grounded aluminium alloy shell which is full of SF6 gas. The epoxy resin is cast into insulation fittings for supporting, bay separating and electrical insulating. The following is a brief introduction of main components:

Breaker: type: ZF1-220, adopting SF6 as insulating and arc extinguishing medium, single-phase, arranged vertically, with incoming and outgoing wires at the both sides of breaker. For this type of breaker, the operation mechanism is equipped to every phase which could be operated in single phase or in 3-phase electrical linkage.

Isolating switch: 2 types: straight line type and right angle type; equipped with electric spring mechanism or dynamo-electric mechanism; one fracture of direct acting plug-in structure on each phase; and an observation window on the shell near the fracture.

Earthing switch: 2 types: common type and high-speed type; grounded directly; for common earthing switch, the electric mechanism is equipped to each phase and the electric spring mechanism for high-speed type. This kind of switch possesses the capability to eliminate troubles through forming short circuit. And an observation window is on the shell of earthing fracture.

CT: single-turn cored structure/straight through structure; HV energized conductor as primary winding; the secondary winding enlaces the ring iron core evenly and is located in the metal shell; full of SF6 in CT as insulating medium for primary winding, secondary winding and grounded shell.

PT: electromagnetic type; primary and secondary winding on the iron core; located in metal shell; full of SF6 in PT as insulating medium against ground; the terminal of secondary winding is led out from sealed terminal box.

Bellows: made of stainless steel; flanges welded at both ends; for its total deformation tolerance along axial direction: ±3mm in radial direction; operation compensation value: ±10mm; installation compensation value: ±10mm axially.

Electrical control cubicle: one control cubicle in one bay; on its panel, there are various signals and main wiring connection presented by simulating wiring. In cubicle, there is the electrical operation and control system of 3-phase breaker, isolating switch, earthing switch and the electric interlock control system among the elements.

The others: busbar, connecting cylinder, and all kinds of elbows are single phase concentric cylinder structure; the outgoing bushing is a hollow porcelain one and full of SF6. The bushing could be installed in normal way or reverse way.

The division of bay: according to the requirements of operation, monitoring, and maintenance and the possibility of structure, connect those air chambers at same air pressure to form a bay. Use bowl-type insulator to separate the same-phase bays to stop gas mixing. Use copper tubes to connect different phases. And for each bay, there should be air charge valve, vent valve and needle-type SF6 density pressure gauge of temperature compensation, which could send out the signal for abnormal air pressure.

The basic installation procedure for ZF1-220 GIS employed in Gaoqiao Substation: check the dimension of civil foundation → set out the centerline at the installation position on foundation → install the breaker and all components in the bay → position the electric control cubicle → install SF6 vent tube and density relay in the bay → install short circuit connector and grounding wire between 3-phase shells → perform leakage test → pump the vacuum → fill in SF6 → check wire connection → check mechanism operation → recheck the leakage and measure the moisture content of SF6 → execute the AC withstand voltage test, insulation resistance test, etc. → carry out inspection and acceptance.

GIS installation is a very complicate and delicate job. Before installation, the preparation for technology and organization must be well done. The staff involved in GIS installation must be settled specially. And prior to installation, a detailed explanation on technology and safety should be given to the involved personnel to make them acquaint the key steps and safety matters in the process of installation. The technical personnel from construction party should follow the Manufacturer’s Installation and Operation Instruction and the relevant technical documents and compile the detailed construction procedure in advance, which should also be approved by the manufacturer, the owner and the supervision party. Only in this way could GIS installation quality be guaranteed. Meanwhile, the following steps should be taken earnestly:

4.2 Check the equipment packing for damage. Verify all components, accessories, spare parts and special tools: complete and free from damage, deformation, and corrosion; porcelain elements free from crack; the insulators free from wetting, deformation and scale. The terminals, inserting parts and loaded parts of GIS should be clean and no corrosion with a record.

4.3 GIS installation field must be cleaned. The installation should be carried out in the circumstance of no sand, no rain and snow. Further more, the relative atmosphere moisture should be ≤ 80%. The proper dustproof and damp-proof measures should be employed. The field must be kept clean all the time. The involved construction personnel must wear clean working clothes. And all items in their pockets must be taken out to avoid any matters falling into the interior of equipment.

5.1 As per 220kV GIS foundation drawing, check the dimension of foundation concerned with GIS installation (based on manufacturer’s installation drawing). The maximum allowed deviation for all dimension is ±5 mm. The position and dimension of foundation embedded parts should accord with the foundation drawing for GIS installation. The difference from the highest to lowest point should ≤ 2mm. For the others, check them one by one as per foundation requirement.

5.2 Mark out the centerline. As per 220kV GIS foundation drawing, mark out the centerline on the floor (including centerline of each branch bay of GIS, main busbar and local control cubicle) with deviation ≤ 5mm per 10m.

5.3 Install GIS as per 220kV GIS General Layout Drawing. First, position the breaker at a distance of 650mm for A, B, C, 3 phases. Attention: after the first breaker is positioned, use a shim to elevate it about 10mm. And the end surfaces of 2 flanges on its top and at the bottom should be vertical to the floor. A water level gauge could be adopted to check and adjust it so that some space could be left for adjusting the equipment in the bays later. Second, regarding the breaker as reference, follow the component assembly sequence in Bay Assembly Drawing and the ex-factory serial number to install them. At the same time, install their supports. Then, install outgoing bushing according to Assembly Drawing.

5.4 Once one bay is finished, the main loop resistance should be measured and internal gas leakage test should be performed. Compare the value of loop resistance in each bay with ex-factory report to check it in accordance with requirement.

5.5 Position the electric control cubicle and then connect the cubicle to all of the electric elements as per wiring connection diagram, including the secondary control cable connection among breakers, isolating switches, earthing switches, CT and PT.

5.8 Under the condition of no leakage after qualitative leakage test, fill each bay with SF6. But before filling gas, each air chamber must be vacuumized. The pipe from vacuum pump to air chamber should be as short as possible. And vacuum pipe and its joints should not have any leakage. Pump vacuum as follows: first, pump the air chamber till less than 1 Torr (1 torr=133.32Pa). Then, continue the action for 1h and observe for 12h. If the vacuum degree decreases but within 2 Torr, it’s possible to continue to pump till less than 1 Torr and fill into SF6. After the pressure is stable, its value should reach to the rated working pressure that each bay should reach to.

After GIS is installed, it must go through strict inspection and test. Until the installation is confirmed correct and reliable, GIS could be put into commissioning. For this reason, the following inspection and test items must be performed on the jobsite. Only after they are qualified, could this equipment be released for operation.

6.1 Perform the overall appearance inspection for the equipment, mainly including: assembly of each component, tightening of components, the arrangement of grounding terminals, all kinds of gas pipeline. Check the above items comply with the design requirements.

6.2 Check the overall wiring connection: check the wiring from control cubicle to the operation mechanism of breaker, isolating switch, earthing switch and other elements; check the terminal box wiring from control cubicle to CT, PT and other elements; and check the tightening and tags of terminals at the same time.

6.3 Measure main loop resistance: before integral assembly, measure the resistance of main loop of the breaker, isolating switch and earthing switch. After installation, measure the main loop resistance in each phase of every bay. The main loop resistance value should not exceed 20% of the ex-factory test data.

6.4 Use one 1000V Meg-ohm meter to measure the resistance of main loop against ground as well as control loop against ground. The resistance of main loop against ground should be above 1000 mega ohm, control loop above 2 mega ohm.

6.5 Check the reliability of contact action of temperature-compensation needle-type pressure gauge. When the pressure of breaker is charged to 0.5MPa (at 20oC), check the block signal. Then, charge to 0.55MPa (at 20oC) and check the alarm signal. When other bays are charged to 0.35MPa (at 20oC), check the signal alarm. After that, fill into SF6 and the value should reach to the rated pressure after it is stable.

6.6 Mechanical operation test: breakers & isolating switches have undergone mechanical operation test and adjustment. But they still need undergo the mechanical operation test after delivery to jobsite so as to check its action. For breakers, apply the hydraulic mechanism to open and close it slowly. If no abnormal conditions, apply the hydraulic mechanism to operate it for 3 times quickly at the rated voltage and oil pressure to check the action signal etc. And its action time is as follows:

Meanwhile, the isolating switch should satisfy the interlock requirements when the breaker and earthing switch are in the Off-position. First, manually operate the operation mechanism to check the action of each part. If normal, operate it electrically for 3 times to check the action.

6.7 After installation, fill SF6 to rated pressure. Check some possible leakage position with a SF6 detector. Use a piece of plastic film with thickness of 0.1mm to wrap the flange connection at outer shell, and then, use adhesive tape to stick the plastic film along the edge of outer shell or use the bandage to bind the film. When tie up, a small space between the film and the detecting position should be remained. 12h later, use a detector with sensibility ≥ 10-8 to check the leakage.

6.8 Measure the water content in each bay. Fill SF6 into each bay to the rated pressure. 24h later, measure the water content in each bay with a moisture micro-analyzer. And the results should comply with the following requirements:

6.9 Insulation withstand voltage test: after GIS installation on field, the insulation withstand voltage test for main loop is the final inspection for the entity assembly before commissioning to prevent any accidental factors (such as the damage during transportation, installation mistakes, matters left behind in the interior, etc.) from causing the internal troubles. The test procedure and program should be discussed by the manufacturer and the user. In a word, each part of GIS main loop must be at least applied the test voltage for once, but avoid the repeated withstand voltage as much as possible. The specified test voltage should be charged between the conductor of each phase and the grounded outer shell. And the voltage could be charged from bushing. The test should be performed on one phase one time with the other two phases grounded. During test, the secondary winding of CT should be short connected and grounded.

6.10 Interlock test: operate all components to check the interlock between breakers and earthing switch of isolating switch box. The interlock must accord with the interlock conditions stipulated in the electrical control schematic diagram.

GIS combined electric apparatus has its unique structure and production flow. During field installation, the installation requirements must be complied strictly. Only in this way could the installation quality be warranted.

7.2 The field must be kept clean all the time. The involved construction personnel must wear clean working clothes. And all items in their pockets must be taken out to avoid any matters falling into the interior of equipment.

7.3 The breakers and isolating switches are transported with SF6 at pressure of 0.05MPa inside. Thus, after they are delivered at jobsite, check the air pressure. If the pressure drop is detected, perform the leakage test and repair the leak sources.

7.4 The smoothness and cleanness of sealing face will impact the air tightness. Thus, the sealing face, sealing groove and O-ring on the connecting flanges between the components must be cleaned by using of clean silk cloth or high-quality tissue. Especially for O-ring, check its specified dimension, property and service deadline at first, and then, check it for damage.

7.5 Absorbent should be baked for 5h in the oven at 300oC. Then, the duration from the absorbent taken out of the oven to enclosing into GIS should be within 30 minutes. And it’s required to vacuumize immediately after absorbent is installed to avoid the invalidation of absorbent due to moisture in the air. Once the sealing face of GIS is open, the absorbent should be replaced or re-baked.

The field installation quality of electric equipments plays a very important part in the safe and stable operation in the future. Therefore, prior to the installation of all these equipments, the installation personnel are required to acquaint the procedure, specification and the instruction manual from the manufacturer. And, a detailed installation procedure should be composed ahead and strictly obeyed. Only in this way could the installation quality of electric equipments be ensured.