Particle motion in gas-insulated switchgear for high-voltage direct current transmission

The investigations were carried out in cooperation with .

Particle motion in gas-insulated switchgear 

Gas-insulated switchgears (GIS) are considered essential components of the power supply grid due to their high reliability and long operating experience in the AC grid. Therefore, this well-proven technology is also used increasingly in high voltage DC (HVDC) applications. However, the behavior of gaseous insulations in coaxial electrode arrangements differs significantly under DC field stress from the behavior under AC. Defects in HV insulation often result in partial discharges (PD) which can lead to deterioration of the insulation withstand strength and which may trigger a breakdown and overall failure of the entire insulation system.

In GIS, metal free-moving particles are a major source of PD. These get into the GIS during manufacturing and assembly, but may also be generated during operation (for example, from mechanical abrasion during switching operations). The electric field strength at which a free moving particle lifts off and bounces between the cathode and the anode depends on its geometry and mass.

Hopping of a chip-shaped particle:

In addition to the alternating motion from one electrode to the other, other forms of motion may occur, such as ‘firefly’. Firefly is characterized by a rapid oscillating motion of the particles in the close vicinity of one electrode, accompanied by light emission and PD. The emitted PD signals can be recorded with conventional (IEC 60270) and unconventional PD measuring techniques (optical, acoustic and UHF-technique). The transition between the individual types of motion is continuous and is affected by the amplitude and polarity of the applied DC voltage, as well as the geometry and mass of the particles.

Cylindrical-shaped particle during Firefly motion:

With very high electric field strength particle-triggered gas breakdown may occur, which can damage the asset and lead the outages in power supply. In the institute's laboratory, these movements are recorded with a high-speed camera and assigned to the characteristic PD pulse sequences.

Breakdown triggered by a spiral-shaped particle:

Further literature can be found at the links listed below:

https://www.researchgate.net/publication/349718657_Dielektrische_Prufung_von_HGU-GIS

https://www.researchgate.net/publication/337922630_UHF-PD_Measurement_and_High-Speed-Imaging_of_Firefly_Motion_at_the_Positive_Electrode_in_HVDC-GIS

https://www.researchgate.net/publication/334665756_Combined_Characterization_of_Free-Moving_Particles_in_HVDC-GIS_Using_UHF_PD_High-Speed_Imaging_and_Pulse-Sequence_Analysis