In this paper, the basic concepts of dynamic thermal ratings of overhead transmission conductors are discussed. The sensitivity of these ratings with ambient conditions is evaluated. Innovative concepts in the measurement of overhead sag are given and correlated with dynamic rating of overhead transmission conductors. Dynamic transmission line thermal ratings take on increased importance in the deregulated electric power industry, since transmission capacity is sold as a deregulated commodity. Also, the electric utilities are under pressure to utilize all their transmission resources to the fullest.
Since August 1989, 222Rn groundwater samples from across the state of Arizona have been collected and analyzed using liquid scintillation. Of the 253 specimens acquired, 65% have 222Rn concentrations above 11 Bq L-1 (300 pCi L-1), while 16% have 222Rn activities over 37 Bq L-1 (1,000 pCi L-1). The geometric mean 222Rn concentration for all the wells tested is 13 Bq L-1 x divided by 4; the arithmetic mean is 37 +/- 122 Bq L-1. Using the geometric mean, it is estimated that an additional tracheobronchial lung dose equivalent of 0.19 mSv y-1 x divided by 13.9 is delivered to Arizona residents from the well water to home pathway.
Underground air returns have been found to be active transportation pathways for radon gas entry into homes. Several homes for which underground air returns were contributing to elevated indoor 222Rn concentrations were evaluated for possible mitigation. Two houses with such problems were successfully mitigated by inserting flexible ducts into the returns. In one of these houses, the initial mitigation attempt resulted in an exacerbation of the problem due to leakage of the ducting. This was solved by re-sleeving the returns using a stronger material. Mitigation of elevated indoor radon gas caused by use of underground air returns by inserting flexible ducts is not possible for all situations, especially those for which the returns are small, filled with debris, misaligned, or inaccessible.
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