Earthing shock safety design standards

摘要

This paper examines the physiological basis for shock safety standards, and how previously conflicting ambiguous standards are being re-aligned in Australia and other countries, using quantified risk analysis to calculate risk of fatality as the new design metric. While a simple one ohm grid resistance may be an adequate design target (even for a substation with a 50kA earth fault level, provided the power cable systems are intact), it has been universally recognised that tolerable touch voltages are a more appropriate metric for safety standards. However, discussions with over 100 engineers from 13 countries have shown that there is a large variety in approaches, ranging from blanket application of standard template configurations (independent of boundary conditions and approach applicability checks) to individually designed and commissioned installations. The new risk based design metric enables designers to more objectively justify the standard to apply for each exposure location.