Streamer propagation in rod-plane air gaps with a dielectric barrier

Abstract-The complex geometry of gas-insulated substations makes it difficult to predict withstand voltages. A key challenge is the characterization of the interaction between electrical discharges and dielectric surfaces. A 60 mm rod-plane air gap with a dielectric barrier is stressed with positive lightning impulse, initiating discharges that are characterized with a PMT, a current measurement system and a high-speed camera. The discharges do not lead to breakdown at the tested voltages. The residual potential on the barrier is measured with a potential probe. Depending on the gap distance, the potential distribution is either bell-shaped or saddle-shaped. The saddle-shape appears when back discharges are seen from the electrode to the barrier. Back discharges reduce the surface charge until the voltage between barrier and rod is lower than the rod inception voltage. Charge density distributions are estimated from the measurements using FEM simulations. In addition to streamer discharges, leadertype channels are sometimes observed. They are arrested close to the dielectric surface. Streamers from these channels charge the dielectric barrier additionally.

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“…They propagate along the barrier and charge it ( fig. 1), changing the field distribution and the following discharge development [9].…”

Section: B Streamer-dielectric Interaction Under Impulse Voltagesmentioning

confidence: 99%

“…Previous work by the authors [9] documented the spatiotemporal propagation of positive streamers in a rod-plane gap with a dielectric barrier. The aim of this work is to further explore the characteristics of electrical discharges in an inhomogeneous air gap with a dielectric barrier.…”

Section: Introductionmentioning

confidence: 99%

Surface charging of dielectric barriers under positive lightning impulse stress

Meyer

Mauseth

Husoy

et al. 2017

2017 IEEE Conference on Electrical Insulation and Dielectric Phenomenon (CEIDP)

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“…This discharge activity was captured in a single long frame of 900 ns in all image series, so it is not possible to determine the propagation speed from the images. Previous work by the authors on similar gaps with dielectric barriers showed that these streamers move with roughly 2 mm/ns, crossing the gap in some tens of ns [4]. In the configurations where d = 20 mm, leader-type channels were not observed.…”

Section: Discharge Developmentmentioning

confidence: 82%

“…Air in combination with dielectrics is a feasible alternative to SF 6 as insulation in MV switchgear [3], [4]. Meeting clearance requirements in air-insulated medium voltage (MV) substations requires accurate withstand voltage prediction models of the dielectric design.…”

Section: Introductionmentioning

confidence: 99%

Breakdown in short rod-plane air gaps under positive lightning impulse stress

Meyer¹,

Mauseth²,

Pedersen³

et al. 2017

NORD-IS

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Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20-100 mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20 mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few µs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.

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“…With dielectric barriers in the discharge path, streamers typically propagate along and around the barrier to ground [11], [22]. Barriers can also inhibit secondary streamer development [23], cause leaders to propagate a longer path in the gas phase [24] or stop them [25].…”

Section: Rod-plane Gaps With Dielectricmentioning

confidence: 99%

Breakdown mechanisms of rod-plane air gaps with a dielectric barrier subject to lightning impulse stress

Meyer

Mauseth

Pedersen

et al. 2018

IEEE Trans. Dielect. Electr. Insul.

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The complexity of gas-insulated substations makes it difficult to predict withstand voltages. Modeling interaction between dielectric surfaces and electrical discharges is a key challenge. In this study, 60 mm rod-plane air gaps with a dielectric barrier 20 mm below the rod are stressed with lightning impulses of both polarities. The discharge mechanisms are investigated with a high-speed camera, a photomultiplier tube and a current measurement system. The discharge development and current-velocity relationship is leader-like. With positive polarity applied, a leader propagates from the upper parts of the rod to ground. Negative impulses are characterized by positive leader development from the ground plane to the rod. For both polarities, the discharge starts with streamers propagating from the rod to the barrier. Positive streamers typically reach the opposite electrode without causing breakdown directly. The findings imply that empirical breakdown prediction models for short air gaps should involve conditions for positive leader initiation and development. The results also show that dielectric barriers increase the breakdown voltage by impeding leader development. The barriers increase the shortest discharge path and shift the point of leader inception further up on the rod.

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Streamer propagation in rod-plane air gaps with a dielectric barrier

Cited by 8 publications

References 6 publications

Surface charging of dielectric barriers under positive lightning impulse stress

Surface charging of dielectric barriers under positive lightning impulse stress

Breakdown in short rod-plane air gaps under positive lightning impulse stress

Breakdown mechanisms of rod-plane air gaps with a dielectric barrier subject to lightning impulse stress

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