Inhomogeneous field breakdown in GIS-the prediction of breakdown probabilities and voltages. III. Discharge development in SF/sub 6/ and computer model of breakdown

This study addresses the dielectric performance of nonpolar hydrocarbon liquids and mineral oils under positive polarity stress. It is of interest to improve knowledge on how functional properties of dielectric liquids vary, as new brands arrive in the market, and existing standards are unsuited for documenting the dielectric functional parameters of these new liquids. Stopping length for nonbreakdown streamers, breakdown voltages and velocities for various pre-breakdown streamer modes have been studied for a selection of model liquids (cyclohexane and white oils), for a gas to liquid oil, and a refined naphthenic transformer oil. Studies of propagation modes were done using an 80 mm point to plane gap and a step voltage with a 0.5 μs rise time. Light emission and pre-breakdown currents have been recorded and instantaneous velocities have been derived from images of propagating streamers. There are clear differences in streamer stopping lengths and mode occurrence and mode velocities between these liquids. The differences seem to be influenced by molecular sizes governing evaporation energy for streamer formation and by concentration of aromatics which can be coupled to electron avalanche processes in the streamer heads.

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“…Practical considerations for use in gas insulated substations are widely documented, see e.g. [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Prebreakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 1: behaviour at positive polarity

et al. 2020

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“…Vcr is defined as the boundary region where the background electric field Eb exceeds the critical value Ecr for effective ionization (for SF6, (E/p)cr·p = 88.5 kV/cm); vc is defined as the boundary of the space charge diffusion region. The dissipation time of the charge in the gas zone (tsw) depends on the electric field distribution in front of the discharge channel [10]. If the applied background electric field slowly increases, the charge diffusion region vc moves in front of the critical field region Vcr, and the propagation of the discharge stops before it extends to the critical length for streamer (lcr).…”

Section: Discussionmentioning

confidence: 99%

“…In the past few decades, the gap breakdown in stressed SF6 gas under impulse conditions has been extensively studied [6][7][8]. Relevant theories based on the streamer and leader mechanisms have been developed by experiments [9] and simulations [10,11]. The aims of most of these previous studies were the design of the power equipment and the failure mechanisms of the SF6 insulation.…”

Section: Introductionmentioning

confidence: 99%

Partial Discharge Measurement under an Oscillating Switching Impulse: A Potential Supplement to the Conventional Insulation Examination in the Field

et al. 2016

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Partial discharge (PD) detection under oscillating switching impulse (OSI) voltage was performed on three types of insulation defects, including a protrusion on a conductor, a particle on an insulator surface, and a void in an insulator, which are three kinds of the common potential insulation hazards in gas insulated power apparatus. Experiment indicated that the PD sequences under OSI were composed of various combinations of the single pulse, the multiple pulses, and the reverse polarity pulse. The difference between the PD inception voltage (PDIV) and the breakdown voltage (BDV) under OSI voltage was greater than that under alternating current (AC) voltage in some cases, which can provide a more sufficient margin below the BDV for PD diagnosis. The OSI voltage also showed a better performance for exciting PDs with detectable magnitudes from small-scale defects, of which the AC voltage was incapable under our test conditions. The different PD activities with different interfaces under an impulse and a slowly varying voltage were speculated to be associated with the gradient of the background electric field and the space-charge mobility.

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“…where E L (x ) is the electric field in leader channel at position x , and E ave is the mean electric field in the leader channel. When the gas pressure is between 0.1 and 0.5 MPa, the average electric field in leader channel is 3-4 kV/cm [24]. The relatively small voltage drop along the leader channel corresponds to a small difference between U i and U b .…”

Section: Mechanism For Critical Radius Phenomenonmentioning

confidence: 99%

Critical radius phenomenon and mechanism for SF₆ gaps under very fast transient and lightning impulse voltages

Zhang¹,

Wu²,

Wang³

et al. 2017

IEEJ Transactions Elec Engng

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Insulation-related accidents of gas-insulated switchgear, induced by very fast transient overvoltage, have become increasingly serious in high-voltage power systems. A steep-fronted impulse voltage test equipment is developed for studying the discharge characteristics and mechanisms in the SF 6 gap. The influence of the electrode radius on the breakdown characteristic of a fixed-distance SF 6 gap is studied. It is found that discharge behaviors of the SF 6 gap show the so-called critical radius effect. With decreasing electrode radius r, the 50% breakdown voltage of the gap decreases till a critical radius R cr is reached, and then remains practically constant for further reduction of r. R cr increases with decreasing gas pressure and wave front time. Calculation results show that R cr is physically close to the length of the filamentary streamer zone L for negative voltages, whereas for positive voltages, R cr is close to the length of the homogeneous streamer zone l . The critical radius phenomenon is related to the streamer-precursor-leader discharge process in SF 6 gas, which is discovered and explained for the first time in this paper by the proposed critical charge criterion of leader breakdown.

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Inhomogeneous field breakdown in GIS-the prediction of breakdown probabilities and voltages. III. Discharge development in SF/sub 6/ and computer model of breakdown

Cited by 33 publications

References 5 publications

Prebreakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 1: behaviour at positive polarity

Prebreakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 1: behaviour at positive polarity

Partial Discharge Measurement under an Oscillating Switching Impulse: A Potential Supplement to the Conventional Insulation Examination in the Field

Critical radius phenomenon and mechanism for SF₆ gaps under very fast transient and lightning impulse voltages

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Inhomogeneous field breakdown in GIS-the prediction of breakdown probabilities and voltages. III. Discharge development in SF/sub 6/ and computer model of breakdown

Cited by 33 publications

References 5 publications

Prebreakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 1: behaviour at positive polarity

Prebreakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 1: behaviour at positive polarity

Partial Discharge Measurement under an Oscillating Switching Impulse: A Potential Supplement to the Conventional Insulation Examination in the Field

Critical radius phenomenon and mechanism for SF6 gaps under very fast transient and lightning impulse voltages

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Product

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Critical radius phenomenon and mechanism for SF₆ gaps under very fast transient and lightning impulse voltages