C-GIS combines SF6 insulation technology with air insulated metal enclosed switchgear manufacturing technology to produce a metal box sealed switchgear. C-GIS for short. The commonly known inflatable cabinet often refers to the general term of C-GIS and inflatable ring-network cabinet.
GIS is a cylindrical container filled with SF6 above 0.3MPa for voltage levels of 72.5~550kv and above. C-GIS is a cabinet mounted container, also filled with 0.3MPa SF6.
The structure of the 40.5Kv C-GIS cabinet is a box-type single bus, one gas compartment or two gas compartments. Its main technical parameters are: rated current 2500A ~ 1250A and below, one minute power frequency withstand voltage 95kV, lightning impulse withstand voltage 185kV, rated short-term withstand current 31.5kA, rated peak withstand current 80kA, rated short-circuit open current 31.5kA, rated short-circuit turn-off current (peak) 80kA, rated pressure of SF6 gas (20 ℃, gauge pressure): 0.04MPa. For 12~15kv C-GIS, on the basis of 40.5kV, replace the 40.5kV parts with the corresponding parts of 12~15kV, adjust the relevant dimensions, and the basic structure remains unchanged.
C-GIS uses low-pressure gas insulation dielectric, solid insulation materials and specific insulation structures to seal or seal high-voltage conductors or high-voltage components to meet the requirements of rated insulation; to carry current by connecting conductors, switch elements and cables; to control, break and protect lines and equipment by vacuum interrupting technology.
It uses modern sensing technology, digital technology and communication technology to control, protect, monitor, display, record and other intelligent management.
1、Basic cabinet type
C-GIS according to the use of cabinets can be divided into incoming cabinets, outlet cabinets, bus cabinets, busbar lifting cabinets, measuring cabinets and so on.
According to the functions and main components of each cabinet-type compartment, it can be divided into: circuit breaker gas cabinet, three-position isolation switch (including bus or part of bus) air cabinet, cable compartment, control and instrument compartment, mechanism compartment, pressure relief compartment, solid insulated bus or bus couplings, etc.
Determination of inflation pressure of medium pressure C-GIS SF6 gas.
First of all, the medium pressure C-GIS is to select the SF6 gas charging pressure in the low pressure range (generally less than 0.25MPa). The gas pressure will also drop. Considering that the annual air leakage rate is limited to less than 1%, the minimum inflation pressure determined after 10 years of no air filling and the accuracy of the density sensor should be 0.12MPa.
2、Shell design
a. The best rated inflatable pressure is selected according to the basic parameters of medium voltage C-GIS, which requires rated insulation level at the minimum functional pressure.
b. Whether the inflatable shell adopts vacuum technology in the process of use, and the maximum pressure difference that may occur.
c. The strength to withstand earthquakes.
Determine the designed seismic force, that is, horizontal acceleration 0.15g (equivalent to seismic intensity 8 degrees) or horizontal acceleration 0.3g (equivalent to seismic intensity 9 degrees), resonant sine wave and safety factor, adding earthquake on the foundation.
d. The rising level of pressure in case of internal arc failure and the release pressure set by the explosion-proof device.
The maximum value of design pressure given in GB3906-1991 can be calculated with reference to the following formula: the maximum value of design pressure MPa (gauge pressure) = (rated inflation pressure (gauge pressure) + 0.1) × 1.3-0.1. combined with the above-mentioned factors, the maximum pressure value which may appear or calculated is determined as design pressure.
Arc extinguishing mode
3. Arc extinguishing mode
At present, the SF6 arc extinguishing chamber mainly adopts the principles of pressure type and self-energy arc suppression.
Due to the need of insulation and arc quenching, the SF6 gas with higher pressure is needed in the arc extinguishing room, which is generally larger than 0.25MPa. For medium pressure C-GIS, it undoubtedly increases the number of gas chambers and improves the sealing requirements. When the current crosses the zero line, the SF6 interrupter relies on the pressure difference between the dynamic and static contacts to form an arc blowing air flow to extinguish the arc. The establishment of this pressure difference requires a large distance and stroke between the contacts, and the design of the C-GIS three-position isolation switch. The structure of the three-position isolation switch can be divided into two types: the straight conductive rod type and the rotating knife type.
4、Interlocking between C-GIS primary components– interlocking conditions determined according to the above typical primary wiring scheme
a. When the circuit breaker is in operation or in the closing position, the three positions are separated from the lock and cannot be operated.；
b. The circuit breaker is locked during the operation of the three-position isolation switch；
c. When the three-position isolation switch is in the grounding position, the state of the cable side circuit is detected by the cable side high voltage live display device, and the circuit breaker can be closed only when the circuit is confirmed to be out of power；
d. When the circuit breaker and three-position isolation switch operate normally, they can be operated remotely, but they can also realize local electric operation. There should be electrical interlock between remote electric operation and local electric operation；
e. In addition, the manual operation and electric operation of the three-position isolation switch must also be interlocked, that is, the manual operation cannot be operated electrically, and the electric operation cannot be operated manually.
5、Development trend of C-GIS products
The development trend of medium voltage C-GIS products is high reliability, maintenance-free, intelligent, low cost and modularization.On-site installation is convenient.
a. The new type of insulator with electric field control element gives full play to the material properties of solid insulating medium and can achieve the requirements of reducing size and improving reliability.
b. Non-destructive testing of important parts before assembly, such as non-destructive testing of insulators, sealed box testing, etc.
c. Intelligent. Realize condition monitoring, establish computer-aided maintenance system and fault diagnosis system to monitor the operation of medium voltage C-GIS products, and realize the archiving and recording of relevant operating parameters of important primary components such as circuit breaker, isolation switch and operating mechanism.
d. Reduce costs. Through modular design and specialized production, the cost ratio of medium voltage C-GIS to air insulated switchgear is reduced to about 1.5 : 1.
e. The on-line detection and diagnosis system of insulation aging is studied, and the protection monitoring system to prevent fault accidents is studied.
Post time: Mar-29-2023