Top 5 Critical Process Controls for GIS Installation & Commissioning Ang Top 5 nga mga Kritical nga Kontrol sa Proseso alang sa Pagsulay ug Komisyon ngadto sa GIS

Ang makadaog kini nga papel sa pagpahayag sa mga bulok ug teknikal nga katangian sa GIS (Gas-Insulated Switchgear) nga ekwipo, ug gisulti usab ang daghang mahalagang puntos sa kontrol sa kalidad ug pamaagi sa proseso sa panahon sa on-site installation. Gitungha niana nga ang on-site withstand voltage tests mahimong mogamit lamang sa bahin sa kabuokan sa kalidad ug kahimsog sa pag-install sa GIS nga ekwipo. Kung wala mapalambo ang komprehensibo nga kontrol sa kalidad sa tanang proseso sa pag-install—espesyalmente sa mga pangutana sama sa kalibutan sa pag-install, pagproseso sa adsorbent, pagproseso sa gas chamber, ug testing sa loop resistance—mahimo ra ang ligtas ug maayo nga pag-operate sa GIS nga ekwipo.

Tungod sa pag-develop sa sistema sa kuryente, mas taas na ang mga pangutana sa mekanikal ug elektrikal nga performance sa primary substation nga ekwipo. Taliwala niini, mas advanced nga mga elektrikal nga ekwipo kasagaran napili sa mga substation. Sa dihang itom, ang Gas-Insulated Metal-Enclosed Switchgear (GIS) naglangkob og mas dako nga aplikasyon tungod sa iyang daghang bulok. Taliwala niini, ang on-site installation ug commissioning sa GIS naging usa ka sentral nga aspeto sa pagtukod sa substation.

1. Teknikal nga Katangian sa GIS nga Ekwipo

• Kompakto nga struktura ug gamay nga espasyo

• Taas nga operational reliability ug excellent nga safety performance

• Eliminates adverse external influences

• Mausab nga panahon sa pag-install

• Easy maintenance ug long inspection intervals

2. Key Process Control Points and Control Measures in GIS Installation

Tungod sa taas nga integrasyon ug kompakto nga disenyo sa GIS nga ekwipo, bisan unsa nga paglimot sa panahon sa on-site installation mahimong maghatag og mga hidden risks nga mahimong moadto sa pag-fail sa ekwipo o pati na sa grid accident. Batasan sa karanasan gikan sa daghang GIS substation installations, strict control sa mga sumusunod nga key aspects importante sa panahon sa installation ug commissioning.

2.1 Installation Environment Control

Ang SF₆ gas labi ka sensitibo sa moisture ug impurities, kini nga ang on-site installation environment kinahanglan mastrictly controlled. Tungod kay ang gas chambers kinahanglan mopasabot sa panahon sa installation, ang trabaho mahimong ibutang sa dry, clear weather ug ambient humidity below 80%. Bisang open na ang chamber, ang vacuum processing kinahanglan ipadayon aron mapugos ang exposure time. Para sa outdoor installations, ang wind speed dili dapat mas taas sa Beaufort scale 3. Kon necessary, local shielding measures kinahanglan implementar sa palibot sa open chamber area, ug ang dust generation sa safe zone kinahanglan mastrictly controlled. Ang installation area kinahanglan clean ug orderly.

Ang personnel dili dapat magdula-dula og loose-fiber clothing o gloves. Ang buhok kinahanglan fully covered sa cap, ug ang face masks kinahanglan igamit. Sa high-temperature conditions, cooling measures kinahanglan implementar aron mapugos ang sweat sa pag-introduce sa moisture sa chamber.

2.2 Handling of Adsorbent in GIS Gas Chambers

Ang adsorbent nga gigamit sa GIS tipikahan 4A molecular sieve, kini non-conductive, low dielectric constant, ug free sa dust. Kini nagpakita og strong adsorption capacity ug can withstand high temperatures ug arc exposure. Ang adsorbent kinahanglan dried sa vacuum drying oven sa 200–300°C sa 12 oras. Bisang dried, kini kinahanglan remove ug install sa chamber sa loob sa 15 minutos. Ang chamber nga may installed adsorbent kinahanglan start sa vacuum processing sa agad aron mapugos ang exposure sa air.

Bisan unsa sa installation, ang adsorbent kinahanglan weighed ug recorded para sa future reference sa panahon sa maintenance. Kon ang weight increases by more than 25% sa panahon sa inspection, kini nagpakita og significant moisture absorption ug needs regeneration. Ang adsorbent gikan sa arc-extinguishing chambers dili dapat iregenerate.

2.3 Vacuum Processing of Gas Chambers

Ang vacuum processing kinahanglan ipatuman sa agad human sa chamber assembly. Ang check valve kinahanglan install sa connecting pipeline, ug dedicated person kinahanglan monitor sa proseso aron mapugos ang backflow sa pump oil sa chamber kon may power failure. Ang vacuum pump kinahanglan start sa unang lugar aron verify proper operation bago buksan ang tanang pipeline valves. Sa panahon sa pag-stop, ang valves kinahanglan close bago turn off ang pump.

Human sa abilidad sa internal absolute pressure below 133 Pa, ang vacuum pump kinahanglan ipatuman pa sa additional 30 minutes, then be stopped ug isolated. Ang absolute pressure (PA) is recorded after 30 minutes of standstill. After a further 5-hour standstill, the pressure (PB) is read again. The chamber is considered well-sealed if PB – PA < 67 Pa. Only after passing this seal test can qualified SF₆ gas be charged into the chamber.

Sa panahon sa vacuum processing, avoid prolonged conditions where one side of a disk-type insulator is under rated operating pressure while the other side is under high vacuum, as this may cause mechanical damage. If necessary, reduce the pressure on the pressurized side to below 50% of the rated value.

2.4 Enclosure Grounding

Tungod sa dense internal layout sa GIS, ang electrical clearance between conductors and between conductors and the metal enclosure is very small. In the event of internal breakdown, large fault currents will flow through grounding conductors into the grounding grid. Additionally, because the GIS enclosure is made of closed-loop metallic material, asymmetric system faults can induce significant voltages on the enclosure due to magnetic induction, potentially damaging equipment or endangering personnel.

Therefore, grounding workmanship must meet high standards. Substations using GIS are recommended to use copper grounding grids to minimize total grounding resistance. All connections between the enclosure and the grounding grid must also use copper materials. Due to the presence of disk-type insulators and rubber seals between gas chambers, bonding copper bars must be installed between enclosures. The cross-sectional area of these bonding bars should match that of the main grounding grid.

GIS uses a multi-point grounding scheme. The number and location of grounding points should follow manufacturer and design specifications.

2.5 Main Circuit Resistance Testing

Main circuit resistance testing is crucial in GIS installation. It not only verifies the integrity of contact connections between modules but also confirms the correct phase sequence of the main busbar. For fully enclosed switchgear, correct phasing and reliable connections are especially critical. In practice, rework has occurred due to incorrect phasing or improper conductor connections.

Manufacturers typically provide standard contact resistance values for internal connections. Loop resistance should be tested segment by segment during assembly, allowing early detection and correction of poor contacts. The measured resistance for each section must not exceed the sum of the manufacturer’s specified values for all connections within that section.

After full assembly, a complete loop resistance test should be performed, and the result must not exceed the theoretical calculated value.

Special Note: Loop resistance testing must not be performed on chambers undergoing vacuum processing. Under sub-atmospheric pressure, the dielectric strength inside the chamber is extremely low. Even a few dozen volts can cause surface discharge on disk-type insulators, leaving discharge traces that become weak insulation points and potential fault sources during operation. Therefore, careful checks must be conducted before any resistance measurement to avoid testing on evacuated chambers.

2.6 Withstand Voltage Test

SF₆ gas’s excellent insulation properties enable GIS to achieve compact design. GIS uses grounded aluminum alloy enclosures, and under operating pressure, the gap between internal conductors or between conductors and the grounded enclosure is very small. Due to high factory pre-assembly, critical components are shipped pre-installed. However, component displacement during transport or introduction of tiny impurities during on-site installation can distort internal electric field distribution. Unlike porcelain-insulated equipment, even minor burrs or particles in GIS interrupters can cause abnormal discharge or breakdown.

Therefore, on-site withstand voltage testing serves as the final defense to verify GIS performance and installation quality.

According to acceptance test regulations, the on-site test voltage is 80% of the factory test voltage. For example, for a 110 kV GIS, the main circuit withstand test voltage is 80% of the factory test voltage: 230 kV × 80% = 184 kV, applied for 1 minute. The test should be conducted at least 24 hours after complete gas filling. Surge arresters and voltage transformers should not be included in the test. High-voltage outgoing cables should be tested together after being connected to the GIS. Before the test, insulation resistance should be measured and confirmed satisfactory.

Test Procedure: Increase voltage at a rate of 3 kV/s to the rated operating voltage (63.5 kV), hold for 1–3 minutes to observe equipment status, then raise to 184 kV and maintain for 1 minute. Repeat this procedure for each phase.

GIS that passes the withstand voltage test may be put into service. However, this test cannot detect all potential defects. In service, GIS must withstand not only power-frequency voltage but also lightning and switching overvoltages. The breakdown field strength of SF₆ gas varies with voltage type. For coaxial cylindrical electrode systems, the 50% breakdown voltage of SF₆ can be empirically expressed as:

U₅₀ = (AP + B)μd

Where:
P — Chamber pressure
d — Electrical clearance (mm)
μ — Electric field utilization factor
A, B — Constants dependent on voltage waveform

Thus, breakdown voltage varies with voltage type and polarity. Different internal defects exhibit different sensitivities to various voltage waveforms. Power-frequency AC voltage is sensitive to insulation breakdown caused by moisture, impurities, or metal particles in SF₆, but less sensitive to surface scratches or poor conductor surface conditions.

Therefore, power-frequency withstand tests cannot detect all internal defects. Enhancing process controls during installation and improving overall installation quality remain the most important measures to ensure safe GIS operation.

3. Conclusion

This paper analyzes key process and quality control points in the on-site installation and commissioning of GIS equipment. It demonstrates that on-site withstand voltage testing can only partially reflect the overall quality and workmanship of installed GIS. More importantly, it highlights that only through strict control of every installation process—ensuring full compliance with procedures and work instructions—can GIS equipment be safely and reliably commissioned from the outset.

It is hoped that this summary may serve as a useful reference for colleagues in the power construction industry.