Learnings

Outcomes

2021/22 

EPRI programs cover a variety of topics providing useful lessons that can be applied to our own operations, these may not always relate to the key objectives NGET has in selecting the programs.  In 2021/22, EPRI concluded a supplemental project into the use of synthetic esters in transformers. 

Regardless of the observations about the environmental impacts of synthetic ester, it is held to the same regulatory standards as for mineral oil and its superior environmental performance confers no special treatment when handling spills or accidental releases, i.e., they must be contained as if they have the same properties.  Infrastructure that is commonly installed for preventing release of mineral oil to the environment is not sufficient for doing the same for synthetic ester.  The work by EPRI confirmed through testing the expectation that larger oil/water separators should be fitted on substations where ester filled transformers are being installed.

2022/2023

Analysis of both online bushing power factor and temperature during laboratory testing, it has been shown that oil insulated bushings in poor condition do not only produce an increase in absolute power factor, but also that the increases are influenced by temperature. This could support the diagnosis of in-service bushings where power factor results suggest a deterioration in condition.

A long-term study of the performance of natural and synthetic esters in conditions comparable to a transmission transformer provided a number of outcomes:

Flash and fire points remained stable.
Ageing of cellulose was comparable in both esters and slower than in mineral oil
Ageing of the fluid was more advanced (colour, acid, power factor) in natural ester than in synthetic ester.
Fault gases for synthetic esters are similar to mineral oil, although carbon dioxide and carbon monoxide behaviour are different. Low activity partial discharge (corona) did not generate significant levels of gases, but high activity partial discharge (sparking) did produce gases. Ratio limits were identified to help distinguish between faults.
Performing cold start operations in sub-freezing conditions should not be hindered in a transformer filled with aged mineral oil, natural ester and synthetic ester fluids (as long as their temperature ranges for use are adhered to).

By example it was demonstrated that acoustic emission partial discharge monitoring may be used to enable continued operation of transformers in service as it allows for closer monitoring of key health parameters of transformers with known internal issues.

2023/2024

The low melting point alloy that NGET has successfully deployed for sealing SF6 leaks has been evaluated for transformer oil leaks.  The mould injection method used for SF6 appears to be less suitable than a spray method.  Further evaluation of this technique is being taken forward in NIA2_NGET0049 - Sprayed Metal for Effecting Leaking Transformer Repairs (SMELTeR).

Despite some limitations, robots and their payloads were found to provide useful data and imagery that could make them a beneficial tool for substation inspections.  NGET will continue to participate in more trials with EPRI.  Based on the outcome of the trials, NGET has selected the best performing robot for NIA2_NGET0060 - Robot, AI and Drone Enhanced Detection of Discharge (RAIDEDD).  

Lessons Learnt

2023/2024 (Previous updates in italics)

Monitoring 

GIC (geomagnetically induced current) monitors can validate existing models for current and harmonics during GIC events.  This will lead onto further investigation into whether GIC can be blocked with a capacitor – the monitors will determine the effectiveness. 

One of the portable DGA devices showed exaggerated response to hydrogen at higher concentrations.  This was fed back to the manufacturer to find a solution. 

Certain DGA monitors were found to be affected in their measurement of methane and ethane by the presence of propane and propene.  This was fed back to the manufacturers who are working on solutions. 

Testing in the laboratory explored the possibility of performing offline 10kV capacitance and C1 Power Factor tests without removing the bushing tap connections. The results showed excellent agreement and indicated a valuable route forward for offline testing that has less wear and tear on the bushing tap connections.

Acoustic emission monitoring can provide insights that could assist in risk assessment of transformers in service.

Performance testing as part of the evaluation of robots for monitoring in substations has completed and one of the four will be selected for consideration of monitoring payloads. 

Some online DGA monitors were found to produce dropouts or spikes in the data during a power outage, reset, or during loss of carrier gas. It would be helpful if the user of the data had insights from the monitor when the data should be ignored. Without this data processing the dropouts or spikes could be seen as true readings – leading to an incorrect diagnosis of the health of the transformer. In the laboratory evaluations the data are extracted from each monitor using a data export function. 

Alternatives for transformer liquid insulation 

Investigations show that alternative fluids in transformers could lead to the potential for upratings compared with mineral oil. 

Investigations of the environmental impacts and mitigation options for synthetic ester used in transformers largely confirmed existing understanding around the biodegradability and bioaccumulation.  An oil water-separator was tested with synthetic ester and found that it was not able to prevent discharges of emulsified mixtures.  Oleophilic media were found to be successful at removing emulsified mixtures of ester and could potentially be used in conjunction with separators to meet regulatory thresholds of releases from substations to the wider environment. 

Ageing studies of esters were carried out and compared with mineral oil.  The mineral oil was aged in an open (free breathing) transformer and performed similarly to other studies.  It was also considered reasonable to age it under nitrogen, which is less commonly performed, the cellulose was found to age more slowly compared to the open situation but still more quickly than in esters.  The nitrogen blanket also resulted in reduced moisture and slower oil ageing. 

In long term testing, the hardness property of lid gaskets decreased significantly for both natural and synthetic ester filled tanks but not in the case of mineral oil fluid and can be attributed to nitrile rubber backbone degradation and filler migration.  This is being investigated further as part of NIA2_NGET0024_Insulating Dielectrics - Esters & Alternative Liquids.

SF6 leaks 

Trialled SF6 leak seals were successful in preventing leaks completely but only for a limited time (less than 2 years).  The methods can be adapted for complex geometries, but application may take a few attempts and they can be difficult to apply in cold conditions. Further work is required. 

A further 12 months on, all applications, bar the earliest trial, continue to show effective leak sealing on the assets to which they were applied.  

Acoustic monitors show some promise in identifying the location of an SF6 leak, this may be beneficial in indoor situations where gas cameras are less effective.  The geometry of the leak plays a significant part in the ability to detect leaks.  It would seem that the gas leak needs to create some turbulence in the air to generate sufficient noise for detection.

SF6 leak detecting technology mounted on drones were trialled but this presented challenges as the sky provides good temperature contrast from ground level which is lost when viewing leaking equipment from above.  The ground provides less contrast and detection is more difficult.  Further trials found that a drone mounted SF6 camera was able to detect a small leak (< 0.5 kg per annum) that was undetectable from the ground.  The rotors did not disperse the SF6 plume and the drone provides a sufficiently stable platform for the camera to be operated in high sensitivity mode.

Membrane Drying units

Lab trials conducted in 2022 have shown that significant improvements in dehydration can be achieved by incorporating Peltier cooling, larger gas pumps, and changing the oil flow path to circumvent the membrane fibres instead of passing through them. Dehydration efficiency up to 60% seems achievable even with inlet moisture < 10ppm. In addition to improving dehydration performance, implementation of Peltier cooling also enabled a smaller footprint and more lightweight unit that can be deployed more easily. Maintenance requirements are also likely to decrease because Peltier coolers have no moving parts.

The promising results from Peltier tests in 2022 show that the technology is ready for deployment in a field prototype.  The Peltier unit has now been incorporated into a refurbished unit making it smaller and lighter, and easier to install.

Transformer oil leaks

A low melting point metal alloy leak sealing technique, previously investigated for sealing SF6 leaks has been evaluated for sealing transformer oil leaks.  The technique shows promise and appears to reduce oil leaks well when applied as a spray.  This will be further developed in a new NIA project.

The application of molten metal alloy leak sealing to transformers continued to show promise based on the 11 weeks ageing of both a spray and a mould injection approach.  The spray technique required minimal surface preparation and was effective in sealing the leaks, even after the ageing period.  The mould injection approach requires a custom mould for each geometry.  The mould injection was effective in sealing the leak but did demonstrate some degradation in leak sealing over the aging period.

Robots for Substation Inspection

Performance testing as part of the evaluation of robots for monitoring in substations has completed and one of the four will be selected for consideration of monitoring payloads.

In the final report on the first phase of evaluating robots for substation inspection, it is noted that all four robots inspected fell short of perfect for the intended purpose.  All had issues that need to be addressed before they could be allowed to be used unsupervised and autonomously.  All failings were fed back to robot manufacturers who responded positively.  EPRI selected the best performing robot and purchased one for further trials and testing.  Specific learning points were as follows:

• Terrain impacts the robotic locomotion method. Gravel can obstruct tracked systems and cause wheeled systems to slip.  Whereas quadrupedal robots may sink into loose or soft ground, such as mud.
• While robot chassis are IP rated (suitable for outdoor use) the payloads are not always similarly rated.
• Collision avoidance is not fool proof and can fail when sensors fail to detect objects.   Limitations of collision sensors may relate to ambient lighting and an obstruction’s movement, shape, size, and colour. 
• Autonomous navigation systems are prone to drift over time, and this can affect repeatability of imagery collection.  GPS suffers particularly.  Visual systems are affected more by lighting conditions and LiDAR misses objects not currently in view.
• Water drops can affect camera lenses.
• The robots support wireless charging.  Their wireless connectivity has limitations during inspections.

Digital Worker

Research suggest that utilities are progressively adopting mobile solutions, but only a small fraction of end-users have fully integrated mobile devices into daily activities.  The majority still require handwritten paper forms for data capture in many tasks. Belief is nearly unanimous that mobile technology can be an advantage for operations and maintenance (O&M) activities, including benefits provided by remote access to data, work instructions and reference materials. Ease of data capture and enforcing consistent reporting processes were opportunities to speed work completion and improve quality. 

There are other relevant concerns regarding new mobile technology programs.  For example, electronic devices could be a distraction to workers and provide opportunities for misuse.  Many utilities either have no plans for mobility programs or have tried to develop programs which were unsuccessful. The largest challenges are seen to be a lack of sufficient human and capital resources to thoroughly plan and execute a well-scoped program. Network connectivity is often unreliable, and applications and devices malfunction. In some cases, the small form-factor of handhelds make useful interaction either a challenge or an impossibility. Other challenges are organizational in nature, such as inter-department cooperation issues and IT reluctance to support new technology programs. An aid to overcoming these issues is involving all stakeholder groups in program planning and execution from day one. 

By reviewing capabilities of modern mobile devices and the O&M process lifecycle, general functional benefits were recognized. Three Use Cases were identified as most likely to provide near-term return on investment: automating work instructions and management, facilitating lockout/tagout, and supporting equipment inspections. Mobile hardware, software and networking factors which could support those use cases were reviewed, and mobile capabilities of software packages currently utilized by utilities showed that very few are optimized for mobile use. Configuration of off-the-shelf software, and custom development of new applications from scratch, are considered very challenging, even under guidance of subject-matter experts. Conducting thorough planning and using agile development and deployment processes can reduce risks.

Dissemination 

Dissemination opportunities in 2021/22 were limited as a result of Covid-19 restrictions.  

Knowledge transfer sessions were held in May 2022, January 2023 and January/February 2024 which provided highlights of current research and an opportunity to discuss projects in detail in Warwick, UK to which other licensees were invited. A similar event will be arranged for January 2025, also in Warwick.  

A paper was presented at the inaugural Polaris International Conference and Exhibition in Glasgow in November 2022.  The paper “Thermal Performance of a Novel Transformer Fluid using a Model Transformer” will be uploaded to the ENA portal along with this report.  It was based on the outputs of work completed in 2021/2022.

A 3-D printed model of the modified membrane dryer for transformer oil was displayed at the Energy Innovation Summit in Liverpool in 2023.

Climate READi (Resilience and Adaptation Initiative) is supported jointly by this project and National Grid US.  The multi-utility project has a dedicated website at www.epri.com/READi which contains more detail about the project, publicly available downloads, and media links to show how the initiative is being disseminated through industry media sources.