35kv Medium Voltage Sf6 Sealed Switchgear

The 35kV medium voltage SF6 sealed switchgear is a factory-assembled, metal-enclosed electrical device that uses sulfur hexafluoride (SF6) gas as both an insulating and arc-quenching medium. Unlike conventional open-type switchgear, all live parts---including the circuit breaker, disconnector, and grounding switch---are hermetically sealed inside a stainless steel tank filled with SF6 gas at a controlled pressure.

What can it do? 

Primarily, this 35kV medium voltage SF6 sealed switchgear is responsible for receiving, distributing, and controlling electrical energy in 35kV power networks. It protects transformers, motors, and feeders from overloads, short circuits, and transient overvoltages. When a fault occurs, the SF6 circuit breaker extinguishes the arc within milliseconds, ensuring minimal damage to downstream equipment. Additionally, it enables remote switching operations and real-time status monitoring, making it a core component of modern smart grids. In essence, it replaces bulky air-insulated switchgear (AIS) in applications where space is limited or environmental conditions are severe.

Product Advantages

When evaluating 35kV medium voltage SF6 sealed switchgear, Lugao Power’s solution stands out through five major advantages:

1. Ultra-High Reliability: Because the SF6 gas provides superior dielectric strength (approx. 3 times that of air), the internal components are immune to dust, humidity, salt fog, and pollution. This results in an extremely low failure rate—less than 0.1% over ten years of operation.

2. Compact Footprint: The sealed design drastically reduces phase-to-phase and phase-to-ground clearances. A typical Lugao 35kV SF6 ring main unit occupies only 1.2m² per feeder, compared to 3.5m² for AIS. This allows utilities and industrial plants to retrofit or expand within existing building footprints.

3. Maintenance-Free Operation: Since all moving parts operate in a dry, sealed SF6 environment, there is no need for regular cleaning, contact adjustment, or insulation resistance testing. The only recommended check is a gas pressure gauge reading once every six months. Over a 20-year service life, this saves up to 70% in operational expenses.

4. Enhanced Safety for Personnel: The metal-enclosed, welded tank is rated for internal arc fault containment (IAC) up to 50kA/1s. Even under an internal fault, the pressure relief valve directs hot gases to a safe exhaust duct—never toward an operator. All interlocks comply with IEC 62271-200.

5. All-Weather Performance: From -40°C in alpine substations to +55°C in desert solar farms, this 35kV medium voltage SF6 sealed switchgear operates without derating. No trace heating or air conditioning is required inside the enclosure.

Product Features

● Lugao Power’s 35kV medium voltage SF6 sealed switchgear incorporates the following specific technical features:

1. Welded Stainless Steel Tank: 3mm thick, 316L grade, helium leak-tested to less than 0.1% per year. No gaskets or O-rings exposed to atmosphere.

2. Three-Position Switch: Integrated load break switch, disconnector, and grounding switch in one mechanism. Mechanical interlock prevents incorrect sequence operations.

3. SF6 Pressure Gauge (Temperature-Compensated) : Provides true pressure reading regardless of ambient temperature. Green zone = 0.12–0.14 MPa (absolute). Low-pressure alarm contacts available for remote monitoring.

4. Vacuum Circuit Breaker Option: For feeder protection, a built-in vacuum interrupter with SF6 external insulation combines vacuum’s high breaking capacity with SF6’s insulation strength. Rated short-circuit breaking current: 31.5kA.

5. Cable Compartment: Large, removable front cover allows easy access for cable lug installation. Suitable for single-core copper or aluminum cables up to 500mm².

6. Magnetic or Spring Actuator: Available either as a magnetic actuator (for 100,000 mechanical operations) or a stored-energy spring mechanism (for cost-sensitive projects).

7. Front Panel Mimic Bus: A clear, engraved one-line diagram with LED indicators for switch position, earthing status, and SF6 pressure.

8. Auxiliary Contacts: 6NO + 6NC, rated for 220V DC, directly driven from the main shaft (no cams to slip).

Product Application

The versatility of 35kV medium voltage SF6 sealed switchgear makes it suitable for the following applications:

1. Wind Farms: Used in each turbine’s tower base or in offshore platform collector rings. Withstands vibration, salt spray, and confined spaces.

2. Solar PV Power Plants: Installed at combiner box outputs and step-up transformer primary side. The sealed design prevents dust ingress in desert environments.

3. Industrial Substations: Steel mills, cement plants, and petrochemical facilities where continuous production requires high uptime. The SF6 switchgear feeds large motors (3MW–10MW) and arc furnaces.

4. Data Centers: Provides reliable 35kV incoming supply to backup generators and UPS systems. Its compact size leaves more floor space for IT racks.

5. Railway Traction Substations: For electrified railways at 27.5kV or 35kV systems. The SF6 switchgear handles frequent switching (up to 5,000 operations/year) without contact wear.

6. Underground Substations: In city centers or commercial complexes where land is prohibitively expensive. The switchgear can be stacked in two tiers inside a 2.5m-high vault.

7. Utility Secondary Distribution: As a ring main unit (RMU) for feeding residential blocks or small industrial parks from a 35kV loop.

Standards We Comply With

Lugao Power’s 35kV Medium Voltage SF6 Sealed Switchgear is designed and manufactured according to international and industry standards to ensure safety, reliability, and long service life.

Production Details

Every unit of Lugao Power’s 35kV medium voltage SF6 sealed switchgear undergoes rigorous manufacturing steps:

● Tank Fabrication: Laser-cut 316L stainless steel plates are robot-welded in a jig. All welds are inspected with dye penetrant and X-ray for pinholes. Each tank is then pressure-tested at 0.3 MPa (2*operating pressure) for 24 hours.

● Surface Treatment: Exterior is phosphated and coated with RAL 7035 epoxy polyester powder (minimum 80μm thickness). Salt spray resistance: 1,000 hours.

● SF6 Gas Processing: After assembly of all internal components (bushings, contacts, actuators), the tank is evacuated to < 10 Pa. Then SF6 gas with purity >99.97% is filled to 0.12 MPa absolute. Dew point is verified at < -50°C.

● Mechanical Endurance Test: Each operating mechanism is cycled 500 times (open/close/earth) on a test bench before final assembly.

● High Voltage Test: 70kV/1min power frequency withstand voltage (dry) and 110kV/1.2/50μs lightning impulse test.

● Partial Discharge Measurement: Less than 5pC at 1.1× rated voltage (38.5kV). Measured with a wideband PD detector.

● Leak Detection: A sniffer probe (halogen detector) scans every weld seam and bushing flange. Leak rate guaranteed < 0.1% per year.

● Traceability: Each switchgear receives a unique QR code. The QR code links to a factory test report including pressure test curves, PD levels, and gas fill date.

SF6 Sealed Switchgear vs Air-Insulated Switchgear (AIS)

Frequently Asked Questions (FAQ)

Q1: How often does the 35kV medium voltage SF6 sealed switchgear need refilling?

A: Under normal conditions, the leakage rate is below 0.1% per year. At 0.12 MPa initial fill, it would take over 20 years to drop to the alarm threshold (0.10 MPa). We recommend checking the pressure gauge every 6 months. No refill is typically needed within the one-year warranty period unless there is a seal failure.

Q2: Is SF6 gas environmentally harmful? And does Lugao offer alternatives?

A: SF6 has a high global warming potential (GWP = 23,500). However, Lugao’s 35kV medium voltage SF6 sealed switchgear uses less than 2kg per unit, and our sealed tank design virtually eliminates emissions. For projects requiring green gas, we offer an optional “Green Gas” (C5-FK) fill with 99% lower GWP, though at a slightly reduced insulation rating.

Q3: Can this switchgear be used outdoors without an additional enclosure?

A: Yes, the 35kV medium voltage SF6 sealed switchgear itself is IP67-rated for the sealed tank and IP4X for the low-voltage compartment. However, for direct outdoor installation, we recommend ordering the “weatherproof hood” option (adds IP54 rating to the entire cubicle). Otherwise, install it inside a basic kiosk or substation building.

Q4: Does the one-year warranty cover the SF6 gas itself?

A: Yes, if a leak is confirmed (using a soap bubble or detector test) during the warranty period, Lugao will supply a replacement gas cylinder and reseal the fitting at no charge. However, if the leak results from physical damage (e.g., a forklift hitting the tank), the repair is billable.

Q5: Can I retrofit a remote SCADA interface to this switchgear?

A: All units come with standard 6NO+6NC auxiliary contacts ready for connection to a RTU or PLC. For advanced monitoring, we offer an optional plug-in module with Modbus RTU (RS485) or IEC 61850 (Ethernet) outputs, providing real-time SF6 pressure, switch position, and operation counter data.

Our Streamlined Production & Delivery Process