Epoxy-based Hermetic Feedthroughs Boost Switchgear Reliability

SF6 Gas Insulated Switchgear (GIS)

Despite its usefulness in gas insulated switchgear since the 1950’s, SF6 is one of the most potent
greenhouse gases with a global warming potential of 23,500 times that of CO2 according to the
Intergovernmental Panel on Climate Change. The insulated switchgear market currently accounts
for 80% of the world’s SF6 usage. Due to its extreme potency and lifespan, the Kyoto Protocol
has listed SF6 among the major substances whose use and emissions should be minimized. In the
US, various states are partnering to transition and retire the use of SF6. Europe has banned in
practically all applications except high-voltage switchgear, and this is only allowed because
alternative technologies are not yet economically viable. Containing SF6 in gas insulated switchgear
remains important for both system function and environmental protection.

Hermetic feedthroughs ensure that water and moisture stay outside of the switchgear while
insulating greenhouse gases stay inside, even if the switchgear were to be submerged in
water. This is especially critical for subsurface switchgear installed underground, yet above
ground equipment must also be storm-hardened for submersion in flood prone areas. Epoxy-based
hermetic feedthroughs are the dominant choice for switchgear applications for a few reasons.

Sensing a Change

To show improvements are being made, requires measurement. The IEC has developed standards
for the measurement of both new (IEC 60376) and used (IEC 60480) SF6 gas. According to the
EPA, California “imposes an annual maximum rate of SF6 emissions that is reduced by 1 percent
over a ten-year period from 2011 to 2020. From 2020 onwards, the maximum emission rate is
not to exceed 1 percent. CARB is also proposing regulatory amendments to phase out use of SF6 in
gas-insulated equipment (GIE) starting in 2025.”1

Sensor technology has advanced to measure multiple properties from a single sensing element such as pressure, temperature, and moisture or humidity. While the sensing element is exposed to gases, the challenge is to seal the electronics used to amplify the signal within a housing. Epoxy-based designs can ensure that the sensing element is able to penetrate the measurement area with a
leak-tight seal.

Hermetic feedthroughs interface between the sensor/transducer and the monitoring system,
HMI, or telemetry unit. A hermetic electrical connector, wire, or cable can protect the sensor in
gas and liquid environments. Hermetic bulkhead connectors protect monitoring equipment while
simplifying the installation or on-site usage. With the decrease in cost of wireless signal transmission and commercialization of many wireless transmission components, the IoT (Internet of Things) industry has seen growth in various industries. In switchgear applications, customers transmit the wired signal from the sealed, SF6 environment to a non-hazardous area with a telemetry unit to wirelessly monitor the gas condition.

SF6 Alternatives

With medium-voltage switchgear, greater progress is being made regarding SF6 alternatives. Europe
has seen the greatest adoption of SF6 free switchgear and ring main units to date. To match SF6 performance while reducing environmental risks, new gases, such as 3M’s Novec™ 4710 series, need to remain stable over temperature with a high dielectric strength. SF6 alternative gases are less toxic in new and used mixtures, reducing operator risk and environmental impact. While the environmental impact is less, the requirement for hermetic and water-tight feedthroughs remains critical to the function and reliability of switchgear equipment.

Oil, vacuum, nitrogen, oxygen, and CO2 are other common alternatives to SF6. CO2 seems the most
promising future material with claims that it will eliminate 10 tons of greenhouse gases over the
switchgear’s lifecycle. Regardless of the type of gas used, it is important that all individual components used within the switchgear assembly are compatible. Further, they must be robust and reliable enough to withstand harsh environments, temperature extremes and regular submersion in water.

Reliable Feedthroughs for Power Equipment

In fact, epoxy-based feedthroughs and connectors meet a range of stringent performance requirements to serve successfully in switchgear applications. These include:

• Truly hermetic with leakage rates less than 1x10^-9 cc-He/sec per MIL-STD-883 testing
• Vacuum to 1 x 10⁸ Torr
• Pressure to 15,000 psi
• Temperatures from -100° to 350°F
• Wire gauges from 38 AWG to 500 MCM
• Conductor counts from one wire to 3200 in a single feedthrough

• Cable lengths to 2000 m.
• High-voltage solutions available, greater than 30kV

Beyond Switchgear: Feedthroughs for Power Distribution

With reliability and stability foundational elements of the power generation and transmission industries, Douglas Electrical Components focuses on the value of high-quality connections and product availability.
Applications where our hermetic feedthroughs are frequently used:

• Transformers
• Network protectors
• Magnetic bearing flywheels used in smart energy storage
• Steam and gas turbines
• Cryogenic gas generation and storage
• Hydrogen fuel cells and generators
• Lithium battery seals
• Oil & Gas instrumentation, compressors, and controls.