Abstract
The expected abolishment of SF6-gas in medium-voltage switchgear has prompted a search for replacements for the switch types that depend on SF6 to obtain the required capability, reliability, compactness, and cost. Ablation of polymers can enhance the arc-quenching capabilities in certain electrical switch designs. Several aspects, like electric arc plasma composition, gas flow, and wall stabilization, must play together to obtain successful interruption. In this paper, open and closed switch geometries and two nozzle materials [polypropylene (PP) and polytetrafluoroethylene (PTFE)] are studied in medium-voltage interruption experiments. Fundamental differences in the arc-quenching process for PP and PTFE are shown. In the case of PTFE, the current interruption performance depends on gas flow resulting from the pressure built up under the high-current period. In the case of PP, the gas flow plays a lesser role for the arc-quenching capability as the interruption capability is large even in an open design with no forced gas flow around current zero. Current chopping happens a few tens of microseconds before voltage zero crossing; thereafter, a remnant conductance in the contact gap is observed, lasting for up to several milliseconds. This can be explained by an arc-to-glow transition in the presence of hydrogen.
Highlights
THE switching of loads and feeders in medium voltage (MV) networks is essential to the operation of medium voltage distribution networks
One approach is to review and improve the technologies that were applied before the introduction of SF6, one of which is the use of arc-induced ablation of polymers that release hydrogen compounds, known as hartgas and wall-gassing
The experimental results presented in this paper, show clearly the fundamental difference of interruption in a PTFE and a PP nozzle
Summary
THE switching of loads and feeders in medium voltage (MV) networks is essential to the operation of medium voltage distribution networks. MV load-break switches are abundant in networks today, and could become even more important in the future, as the complexity of distribution network operation increases. Metal-enclosed switchgear filled with SF6 has provided a compact solution, but due to environmental concerns, manufacturers of these products are seeking for alternative ways to achieve compact and low-cost products. One approach is to review and improve the technologies that were applied before the introduction of SF6, one of which is the use of arc-induced ablation of polymers that release hydrogen compounds, known as hartgas and wall-gassing. Some older switchgear products take advantage of the arc-quenching effect of this ablation, in the MV product range, but there is no comprehensive publication that explains the mechanisms involved
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