• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.587-593
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• 2021

Since 2017, a total of 29 fire accidents have occurred in energy storage systems (ESSs) as of June 2020. The common mode voltage (CMV) is one of the electrical hazards that is assumed to be a cause of those fire accidents. Several cases of CMV that violate the allowable insulation level of a battery section are being reported in actual ESS operation sites with △-Y winding connections. Thus, this paper evaluates the characteristics of CMV. An ESS site was modeled with an AC grid, PCS, and battery sections using PSCAD/EMTDC software. As a result of a simulation based on the proposed model, it was confirmed that characteristics of CMV vary significantly and are similar to actual measurements, depending on the grounding method of the internal transformer for PCS. The insulation level of the battery section may be severely degraded as the value of CMV exceeds the rated voltage in case of a grounding connection. It was found that the value of CMV dramatically declines when the internal transformer for PCS is operated as non-grounding connection, so it meets the standard insulation level.

• Korean Journal of Environmental Biology
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• v.36 no.4
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• pp.567-575
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• 2018

The soil physical quality is a core factor in achieving two of sustainable agriculture's goals: productivity and environment. The purpose of this study was to assess changes in soil physical properties for nearly a decade through periodic monitoring of three cultivation types: upland, orchard, and paddy. Field surveys and lab analysis were conducted to determine the soils physical properties after every 4 years; upland (2009, 2013, and 2017), orchard (2010 and 2014), and paddy (2011 and 2015). In each year soil samples from 162-338 sites were collected. The bulk density of upland subsoil decreased from $1.53Mg\;m^{-3}$ to $1.50Mg\;m^{-3}$ while the plowing depth and subsoil organic matter increased from 13.7 cm to 19.5 cm and from $12.6g\;kg^{-1}$ to $18.3g\;kg^{-1}$ respectively during the period 2009-2017. Plowing depth for orchard increased from 16.7 cm to 18.9 cm. However, organic matter content decreased from $15.9g\;kg^{-1}$ to $15.4g\;kg^{-1}$ during the 2010-2014 period. For paddy, plowing depth and subsoil organic matter decreased from 17.5 cm to 16.7 cm and from $17.5g\;kg^{-1}$ to $15.8g\;kg^{-1}$ respectively. The subsoil bulk density increased from $1.47Mg\;m^{-3}$ to $1.52Mg\;m^{-3}$ from 2011-2015. Excess ratio for soil physical standards increased from 16% to 22% in orchard, 56% to 62% in paddy, and decreased from 41% to 29% in upland. The overall soil physical quality had been ameliorated for upland, but degraded for paddy. Improved tillage practices and application of appropriate organic matter is necessary to enhance the quality of soils, especially in the paddy field.