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Replacing Synthetic Oils in Capacitors


Olatoundji George Gnonhoue
Olatoundji George Gnonhoue Author profile
Olatoundji George Gnonhoue is currently a PhD candidate in Mechanical Engineering at ÉTS.

Amanda Velazquez Salazar
Amanda Velazquez Salazar Author profile
Amanda Velazquez Salazar is a postdoctoral fellow in the Department of Mechanical Engineering at ÉTS and a MITACS Fellow.

Léo Millard
Léo Millard Author profile
Léo Millard is a Master’s student at ÉTS as part of a joint curriculum with Arts et Métiers ParisTech.

Simon Joncas
Simon Joncas Author profile
Simon Joncas is a professor in the Department of Systems Engineering at ÉTS.

Éric David
Éric David Author profile
Éric David is a professor in the Mechanical Engineering Department at ÉTS and is the current department head. His research interests include dielectric and nanodielectric materials, rotating machinery, and underground cable insulation.

Laurent Cormier
Laurent Cormier Author profile
Laurent Cormier is a mechanical engineer and professor in the Department of Mechanical Engineering at UQTR.

Romain Poudret
Romain Poudret Author profile
Romain Poudret is a graduate from Arts et Métiers ParisTech in Engineering and holds a Master’s degree in Mechanical Engineering from ÉTS Montréal.

Ioana Preda
Ioana Preda Author profile
Ioana Preda is associate professor at the Department of Electrical Engineering of the Haute école d’ingénierie et d’architecture Fribourg (HEIA-FR, Switzerland).

High-voltage power plant

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SUMMARY

For decades, the technology to manufacture capacitors used in high-voltage systems required the use of synthetic oils as a dielectric wall. These oils have a harmful effect on the environment and on the health of operators in close contact. This paper presents the preliminary results of a study that proposes the development of oil-free capacitors with a similar or better performance than that of those impregnated with oil. Keywords: high-voltage capacitors, resin, impregnation, film.

Dielectric Walls in Capacitors, a Technology that Needs Upgrading

The development of different insulating materials used as dielectric walls in capacitors has revolutionized capacitor manufacturing technologies. These materials play a key role in load control and energy storage. Before the 1970s, kraft paper coated in mineral oil (polychlorinated diphenol) was the main dielectric used in capacitors. Afterwards, because of their low dissipation factor, high dielectric strength, good stability and high accessibility, polymer films gradually replaced kraft paper in capacitors. The switch from paper to polymer film has also shortened the capacitor manufacturing process by reducing the drying time needed for paper before impregnation with oil (Hantouche, 1996; Qi, Petersson, & Liu, 2014).

Types of capacitors

Fig. 1. Different capacitor configurations (not to scale)

The current manufacturing technology for high-voltage capacitors involves using a stack of thin strips (electrodes and dielectric wall) wound in configurations that may change (see Fig. 1) depending on the expected electrical performance. The wound coils are assembled in series or in parallel, forming the so-called active part of the capacitor. Usually, to protect the active part from air and moisture and to fill possible voids, it is inserted in a waterproof insulator and impregnated with a synthetic oil.

High-voltage capacitor

Fig 2: Oil capacitors

Although synthetic oil capacitors currently have a high electrical reliability, there is a need to upgrade technology to replace synthetic oils because of their harmful effect on the environment and the safety risk they pose in the workplace. In addition, new environmental protection and conservation regulations may prohibit the use of synthetic oils within a few years. Therefore, there is an urgent need to meet the new challenges in dielectric materials and to enable capacitors to meet health and environmental requirements (Samuel, Lucas, Fu, Howard, & Lafon-Placette, 2012).

The characterization project of new dielectric walls based on thermosetting resins, under the supervision of Professors Éric David and Simon Joncas—a research team from the Department of Mechanical Engineering and the Department of Systems Engineering at ÉTS—is presently looking for solutions to replace dielectric oil with thermosetting resins. The properties of the new dielectric system (films & resin) are characterized mainly by using partial discharge (PD) measurements. This technique ensures that the manufactured capacitors are free of cavities or delamination. Indeed, PD occurrences during the capacitor operation damage its dielectric wall. PD measurement is therefore used as a process quality control method, since a sample with PD cannot be accepted.

Table 1: PD, capacitance and dissipation factor measurements at 60 Hz

Partial discharge measurements

Histogram of partial discharge in a capacitor

a)

Histogram of partial discharge in a capacitor

b)

Histogram of partial discharge in a capacitor

c)
Fig. 3. PD histogram under an electrical stress of 40 kV/mm for different samples of oil-free manufactured capacitor; a) Single-layer capacitor with surface treatment, b) Multi-layer capacitor without surface treatment, c) Multi-layer capacitor with surface treatment.

Figure 3 shows the PD histograms for different dielectric wall configurations. Comparing PDs with these results shows that “rabbit ear” type PD patterns were observed in the multi-layer capacitor without surface treatment (Figure 3b). The single-layer capacitor with untreated surface shows a low PD level. The surface-treated multi-layer capacitor does not exhibit PD under an applied electrical stress of 40 kV/mm. These results confirm the quality of the impregnation method, the choice of material and surface treatments as well as the potential use of this new technology.

Conclusion

These preliminary results show a significant increase in performance of the dielectric wall with the surface treatment of films impregnated with a commercial thermosetting resin. Also, in its further development, a single-layer dielectric wall does not appear to be suitable for oil-free applications. 

Additional Information

This paper was presented at the IEEE 2020 International Conference on Dielectrics (ICD 2020) (available shortly).

Olatoundji George Gnonhoue

Author's profile

Olatoundji George Gnonhoue is currently a PhD candidate in Mechanical Engineering at ÉTS.

Program : Mechanical Engineering 

Author profile

Amanda Velazquez Salazar

Author's profile

Amanda Velazquez Salazar is a postdoctoral fellow in the Department of Mechanical Engineering at ÉTS and a MITACS Fellow.

Program : Mechanical Engineering 

Author profile

Léo Millard

Author's profile

Léo Millard is a Master’s student at ÉTS as part of a joint curriculum with Arts et Métiers ParisTech.

Program : Mechanical Engineering 

Author profile

Simon Joncas

Author's profile

Simon Joncas is a professor in the Department of Systems Engineering at ÉTS.

Program : Automated Manufacturing Engineering 

Author profile

Éric David

Author's profile

Éric David is a professor in the Mechanical Engineering Department at ÉTS and is the current department head. His research interests include dielectric and nanodielectric materials, rotating machinery, and underground cable insulation.

Program : Mechanical Engineering 

Author profile

Laurent Cormier

Author's profile

Laurent Cormier is a mechanical engineer and professor in the Department of Mechanical Engineering at UQTR.

Program : Mechanical Engineering 

Author profile

Romain Poudret

Author's profile

Romain Poudret is a graduate from Arts et Métiers ParisTech in Engineering and holds a Master’s degree in Mechanical Engineering from ÉTS Montréal.

Program : Mechanical Engineering 

Author profile

Ioana Preda

Author's profile

Ioana Preda is associate professor at the Department of Electrical Engineering of the Haute école d’ingénierie et d’architecture Fribourg (HEIA-FR, Switzerland).

Author profile


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