A novel approach for basic insulation-level (BIL) enhancement of vacuum interrupters
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ORIGINAL PAPER
A novel approach for basic insulation-level (BIL) enhancement of vacuum interrupters Asaad Shemshadi1 Received: 18 December 2019 / Accepted: 11 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This article introduces a newly developed design method that may be utilized in modern high-voltage vacuum interrupter (VI) design. At first, a typical 24 kV vacuum chamber is modeled using finite-element method. Potential and electric field profiles are derived and analyzed in detail. To continue, the proposed approach which consists of twin metallic rings placed in the porcelain tubular insulator is added to the previous model and the new model is analyzed in three steps: short-, mediumand long-course scenarios. The achieved patterns illustrate the severe reduction in electric field value of the contacts’ surface especially for long-course prototype (up to 74.2%). This phenomenon is discussed in detail. Considering the Fowler–Nordheim quantum tunneling equation; a reduction in electric field intensity brings to lower field emission current value which is the most important factor of breakdown during BIL tests. It is important to note that any reduction in electric field value results in decrease in micro-discharge value and microparticle movement, which are the additional reasons for vacuum insulator failure during high-voltage pulse insertion. This means that the inception voltage of the proposed VI can be increased so that higher BILs like 63 kV insulation high voltage requirements are achieved. The reduction rate of field emission current density is reduced to 4.9% of its initial value for or 120-mm course which expresses the effectiveness of this new approach. Keywords Vacuum interrupter · Basic insulation level (BIL) · Finite element · Electric field · High voltage
1 Introduction Vacuum interrupters are the most utilized medium-voltage, (V < 36 kV), electrical apparatus for interrupting current application in a distribution electrical networks since 1965; the main reason is their heavy-duty, maintenance-free and environment-friendly properties comparing with SF6 circuit breaker. The current will be quenched at the first zero crossing [1–9]. Dielectric behavior of vacuum circuit breaker (VCB) seems to be more critical compared to SF6 apparatus. Low BIL endurance is the main reason that this favorable circuit breaker could not be erected in higher standard voltage levels like 63 kV nominal voltage systems. BIL of a VI depends on the pressure, the distance between electrodes and the materials used for electrode alloy for distances of about 1 cm and pressures of about 10−7 torr; the dielectric strength ranges
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Asaad Shemshadi [email protected] Department of Electrical Engineering, Arak University of Technology, Arak 3818141167, Iran
from 150 to 300 kV/cm. Change in contacts’ alloy and conditioning the protrusions located on the contacts’ surface using high voltage pulses are investigated in detail in previous tasks [10–15]. Investigating breakdown mechanisms in vac
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