Measurement Technology in SF₆ Systems for Power Transmission and Distribution

Gas-insulated switchgear (GIS) operated with sulfur hexafluoride (SF₆) plays
a central role in modern power transmission and distribution. It enables compact,
high-performance and highly reliable installations that remain stable even under extreme
environmental conditions. Since SF₆ is essential for electrical insulation and arc quenching,
its condition and purity must be monitored precisely at all times.

In this context, measurement technology has particular importance: it ensures that
gas pressure, density, humidity, temperature and possible decomposition products are accurately recorded.
These parameters determine whether switchgear can be operated safely and whether
the insulating capability of the gas is maintained in the long term. At the same time, reliable
monitoring helps to detect leaks at an early stage and avoid environmental impact.

The following sections show which measured variables are particularly relevant in SF₆ systems,
which challenges exist and which requirements measurement technology must fulfil in order to
ensure safe and sustainable operation of power distribution and transmission systems.

Relevant Properties of SF₆ for Measurement Technology

Sulfur hexafluoride (SF₆) has a number of physical properties that make it ideal for use
in gas-insulated switchgear – while at the same time placing complex demands on
measurement technology. The gas is barely chemically reactive, offers excellent dielectric
properties and enables compact system designs. However, to ensure safe use, several parameters
must be continuously monitored, as changes in gas quality can directly influence
its insulating capability.

Key Physical Properties

High dielectric strength: SF₆ insulates voltages significantly better than air.
Effective arc quenching: the gas absorbs energy and safely separates electrical contacts.
Low thermal conductivity: influences temperature development in enclosed systems.
Chemical inertness: very stable under normal conditions, but formation of decomposition products in arcs.
Strong temperature–density relationship: density changes depend directly on temperature and pressure.

Relevance for Measurement Technology

These properties make precise metrological acquisition necessary. In particular, the combination
of pressure, temperature and density is crucial for the condition of the gas. At the same time,
humidity and possible decomposition products must be monitored, as they can impair insulation
and cause corrosion.

Measured variable	Relevance	Typical effects in case of deviation
Pressure	Direct indicator of gas quantity and density	Falling pressure values may indicate leaks or temperature changes
Density	Decisive for the insulating capability of SF₆	Insufficient density can lead to electrical breakdowns
Temperature	Influences the measured pressure and density values	Incorrect compensation leads to faulty assessment of the gas condition
Humidity	Indicator of possible condensation and reduced insulation	Increased moisture promotes corrosion and arc formation
Decomposition products	Formed during arcs or thermal stress	Can be toxic and attack materials in the system

Monitoring these variables is important not only for operational safety, but also for
long-term system reliability and compliance with statutory environmental requirements.
Modern measurement technology must therefore be precise, long-term stable and able to detect even the smallest deviations.

Application Areas of Measurement Technology in SF₆-Based Switchgear

In systems for power transmission and distribution, measurement technology plays a central role in
operational safety, system availability and compliance with regulatory requirements. Since SF₆ is used
as an insulating and switching medium, various process and environmental parameters must be
continuously monitored. Any deviation can not only impair system operation,
but also have safety-relevant and ecological consequences.

1. Gas Pressure and Gas Density Monitoring

The combination of pressure, temperature and gas density largely determines the
insulating capability of SF₆. Changes in this balance can arise from leaks,
material ageing or thermal effects.

Monitoring operating pressure in SF₆ tanks and modules
Compensation of temperature effects for correct density determination
Early detection of potential gas losses through trends and alarms

2. Humidity Measurement in the Gas Compartment

Humidity is one of the most critical influencing factors in SF₆ systems. Even small
amounts of water vapour can reduce the dielectric strength of the gas and cause corrosion.

Monitoring of relative and absolute humidity in the gas
Prevention of condensation events in temperature-sensitive areas
Long-term assessment of gas quality

3. Measurement of Decomposition Products

During switching operations or thermal stress, SF₆ can decompose and form reactive
by-products. These can be harmful to health and attack components
in the systems.

Detection of typical decomposition products (e.g. SOF₂, SO₂, HF)
Assessment of gas quality after switching operations
Detection of critical operating conditions through chemical analysis

4. Temperature Monitoring

The temperature in the gas compartment influences both pressure and density.
Precise temperature measurement is therefore essential for any assessment of the gas condition.

Continuous measurement of gas temperature
Correction of pressure values for accurate density calculation
Detection of thermal overload situations

5. Leak Detection and Environmental Monitoring

As SF₆ is a strong greenhouse gas, leak-tightness control and emissions monitoring
have the highest priority. Even small leaks must be detected at an early stage.

Detection of gas losses through continuous trend measurements
Monitoring of critical sealing points and connection areas
Checking the ambient air for SF₆ releases

Tabular Overview of Application Areas

Application area	Measurement tasks	Monitoring objective
Pressure and density monitoring	Pressure measurement, temperature compensation, density calculation	Maintaining insulating capability and early leak detection
Humidity measurement	Detection of water vapour content	Prevention of corrosion and breakdown problems
Decomposition products	Gas analysis, chemical detection	Assessment of gas quality and operational safety
Temperature monitoring	Gas temperature measurement	Correct assessment of the gas condition
Leak detection	Pressure trend, ambient sensors, tightness testing	Minimisation of emissions and avoidance of system disturbances

The application areas mentioned show that measurement technology in SF₆ systems is far more than
simple process monitoring — it is crucial for operational safety, system lifetime
and environmental protection.

Challenges and Requirements for Measurement Technology in SF₆ Systems

Measurement technology in gas-insulated switchgear is subject to special requirements, as SF₆
has both electrical and chemical properties that must be monitored precisely and continuously.
At the same time, mechanical loads, environmental influences
and thermal fluctuations affect the sensors. To enable reliable assessment of the
gas condition, measuring instruments must be specially designed for these conditions.

1. High Accuracy and Long-Term Stability

Since the insulating capability of SF₆ depends directly on density, humidity and purity,
tightly tolerated and reproducible measured values are essential. Even small drift values can
indicate incorrect gas conditions in operation.

Measurement accuracies in the low per mille range
Long-term stable sensors for low-maintenance monitoring
Low temperature sensitivity for outdoor and indoor applications

2. Media Resistance and Robust Design

Sensors and measuring devices must be resistant to SF₆ and its possible decomposition
products. These can have a corrosive effect and impair the materials of the measuring device.

Use of suitable materials (e.g. stainless steel, special alloys, PTFE)
Resistance to fluorides and acid gases
Pressure-resistant and vibration-resistant design

3. Purity and Leak-Tightness of the Measuring Systems

The leak-tightness of all measuring points is particularly critical. Even minor leaks
falsify measured values and can promote SF₆ emissions.

Gas-tight measuring connections and welded components
Minimisation of potential leakage points
Suitable sealing and protection against moisture ingress

4. Temperature Compensation and Pressure-Dependent Measured Values

Pressure and density measurements are strongly temperature-dependent. Measurement technology
must therefore be able to compensate in order to provide correct gas condition values.

Precise temperature measurement at the measuring point
Compensation models for gas-physical relationships
Correction of environmental and load fluctuations

5. Integration into Monitoring and Control Systems

Modern power supply networks increasingly rely on automated monitoring and
diagnostic systems. Measurement technology must therefore be compatible with digital communication protocols
and monitoring platforms.

Support of common interfaces and protocols
Transmission of high-resolution measured values in real time
Compatibility with remote maintenance and diagnostic systems

Tabular Overview of Requirements

Requirement	Description	Relevance for SF₆ systems
High measurement accuracy	Precise detection of the smallest changes in gas condition	Avoidance of misinterpretation in density and pressure measurement
Media resistance	Resistance to SF₆ and chemical by-products	Long service life and reliable operation
Leak-tightness	Gas-tight housings and connections	Avoidance of emissions and falsified measured values
Temperature compensation	Correction of temperature-dependent pressure fluctuations	Reliable assessment of the gas condition
Integration into control systems	Digital connectivity and continuous data transfer	Transparent real-time monitoring

These requirements show that measurement technology in SF₆ systems is far more than a
supporting component: it forms the basis for safe, efficient and
environmentally compatible system operation.

Environmental and Safety Aspects in the Monitoring of SF₆ Systems

Although SF₆ has excellent electrical insulation properties, it is one of the
strongest known greenhouse gases. Escaping quantities have a significant effect on the environment
due to their high global warming potential. For this reason, precise
measurement technology, reliable leak testing and continuous monitoring play a
key role in minimising risks and complying with regulatory requirements.

1. Importance of Emissions Monitoring

Even the smallest leaks can lead to high emissions in the long term. Monitoring
therefore serves not only operational safety, but also environmental and climate protection.

Early detection of minor gas losses through trend-based analysis
Prevention of creeping leaks through continuous density and pressure measurement
Reduction of environmental impact through rapid response

2. Regulatory Requirements and Documentation Obligations

Many international regulations require proof of controlled handling of SF₆.
Accordingly, measured values must be documented, archived and regularly reviewed.

Obligation to record all filling quantities and gas movements
Regular leak tests in accordance with environmental standards
Evidence of emission reduction and gas recovery

3. Safety of Operating Personnel

Although SF₆ is non-toxic under normal conditions, decomposition products can form during arcs or
thermal stress that may be hazardous to health. Measurement technology is used here to identify
potentially critical conditions.

Detection of decomposition products (e.g. HF, SO₂, SOF₂)
Warning of dangerous concentrations in system areas
Checking gas quality after switching operations

4. Impact on System Reliability

Changes in gas condition can impair dielectric strength.
Precise measurement technology makes it possible to detect safety-relevant conditions in good time.

Limiting the risk of electrical breakdowns
Protection against corrosion and material damage
Prevention of unplanned system shutdowns

Tabular Overview of Environmental and Safety Aspects

Aspect	Significance	Measurement-related measures
SF₆ emissions	Reduction of greenhouse effects	Leak detection, trend-based pressure/density measurement
Regulatory requirements	Compliance with legal standards	Documentation, regular testing, archiving of measured data
Decomposition products	Protection of personnel and system materials	Gas analyses, sensors for HF and sulphur-containing compounds
System safety	Avoidance of disturbances and damage	Monitoring of density, temperature, humidity and purity
Operational outages	Minimisation of unplanned shutdowns	Early detection of critical operating conditions

Overall, it becomes clear that precise measurement technology plays a key role in the safe,
sustainable and regulatory-compliant use of SF₆ in power distribution and
power transmission. It helps to reduce emissions, detect hazards
and ensure the reliable operation of critical infrastructure systems.

Future Perspectives and Further Development of Measurement Technology in SF₆ Systems

The energy sector is undergoing technological change, which also affects measurement and
monitoring technology in gas-insulated switchgear. In parallel with increasing requirements
for grid stability, digitalisation and environmental responsibility, measurement technology
is continuously evolving. Modern sensor technology, intelligent monitoring systems and alternative
insulating media have a significant influence on the future design of SF₆ systems and their measurement technology.

1. Digital and Networked Monitoring Systems

In modern power supply networks, predictive condition monitoring is gaining importance.
Sensors no longer deliver just individual measured values, but integrated analyses for assessing
the system condition in real time.

Integration of sensors into digital monitoring platforms
Trend analyses for gas density, humidity and temperature
Automated alarms and diagnostic functions
Linking different measurement points into complete system profiles

2. Advances in Sensor and Analysis Methods

New sensor technologies enable more accurate and faster measurements, particularly in the field of
gas analysis and humidity measurement. Miniaturisation and robust designs also improve use
in compact GIS systems.

Improved selectivity in detecting decomposition products
Higher accuracy at extremely low humidity levels
More durable materials to minimise maintenance intervals
Measurement methods independent of temperature and pressure

3. Predictive Maintenance and Data-Based Forecasts

By recording and evaluating historical measured values, patterns can be identified that
indicate future deviations or failures. Measurement technology thus forms the basis for
predictive maintenance.

Identification of trends and early indicators of leaks
Forecasts of gas ageing processes
Automatic warning messages in the event of shifting limit values
Optimisation of maintenance cycles based on actual data instead of fixed intervals

4. Development of Alternative Insulating Gases

Due to the environmental impact of SF₆, alternative insulating media are becoming increasingly important.
These also require precise and specialised measurement technology, as physical properties
and measurement parameters can differ significantly.

Lower global warming potentials require new monitoring concepts
Measuring devices must be adapted to new gas mixtures
Extended gas analysis for differentiated chemical compositions

5. Higher Requirements Due to Modernisation and Grid Expansion

The expansion of renewable energies and rising energy demand are leading to a growing
number of gas-insulated switchgear systems. This also increases the requirements for their measurement and
monitoring systems.

Continuous loading of systems over longer periods
Higher switching frequencies due to variable generation
Requirements for real-time monitoring of large system networks

Tabular Overview of Future Developments

Trend	Technical significance	Impact on SF₆ systems
Digital networking	Sensors communicate in real time via modern protocols	More transparent monitoring and faster response times
New sensor technologies	Higher precision, lower drift, wider measuring ranges	Improved gas condition assessment and reduced maintenance effort
Predictive maintenance	Data-based condition monitoring instead of fixed intervals	Reduced failure risks and optimised maintenance
Alternative insulating gases	Adaptation of measurement technology to new physical properties	State-of-the-art monitoring for more sustainable insulating media
Grid expansion	Higher loads and operating requirements	More measuring points, extended diagnostic systems

These developments show that measurement technology in SF₆ systems will continue to play a central role –
not only for the safety and reliability of existing systems, but also for
the transformation towards digital, sustainable and highly available power networks.

Conclusion

Measurement technology is a central building block for the safe, efficient and responsible
operation of SF₆ systems in power transmission and distribution. Since the insulating capability
of SF₆ depends critically on density, purity, humidity and temperature, these
parameters must be continuously and precisely monitored. Modern measuring systems enable
reliable assessment of gas condition and help to increase operational safety,
minimise failure risks and extend the service life of switchgear.

At the same time, monitoring of SF₆ systems is an important contribution to environmental and
climate protection. By detecting even the smallest leaks at an early stage, emissions
can be significantly reduced and legal requirements reliably met. Measuring devices also play
a decisive role in identifying decomposition products that may be critical for both personnel
and system components.

With the increasing use of digitally networked sensors, modern gas analysis and
data-based diagnostic methods, measurement technology is continuously evolving. In future,
it will contribute even more to automated process monitoring and play an important role
in predictive maintenance strategies. Even when alternative insulating gases are introduced,
precise measurement technology remains indispensable, as new media place specific demands
on monitoring and analysis.

Overall, it becomes clear that reliable measurement technology is an essential foundation for the
performance, safety and sustainability of modern energy infrastructures. It combines
technical precision with environmental responsibility – and thus creates the basis for a
stable and future-proof power supply.

WIKA Model GD-20-W Gas density sensor with wireless transmission For gas density, temperature and pressure of insulating gases

High-accuracy sensor technology
Wireless LoRaWAN^® output signal
Long battery life
Good long-term stability and EMC characteristics
Compact design

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