Emergency Ratings. If emergency conditions require temporary loading beyond normal continuous current capability, the multiplying factors in Table H1 can be applied, recognizing that such loadings may produce moderate loss of life. Before this is done, revised continuous rating values should be determined using Figure 1 and the emergency ambient temperatures specified in Appendix A. The appropriate factors in Table H1 then are applied to the revised continuous rating values to determine the emergency ratings. Table 1 was originally prepared for the NEPOOL Capacity Rating Procedures using a major manufacturer’s curve of allowable overload following rated load to produce not more than a 1 percent loss of life for an oil-filled current transformer. Values for butyl-molded and compound 1 These curves are based on the assumption that average winding temperature rise are proportional to current squared. filled transformers were extrapolated on the basis of correspondingly shorter thermal time constants than for oil-filled units. Table H 1 Emergency Rating Multiplying Factors Duration of Emergency Transformer Type Oil-Filled Butyl-Molded Compound 0-1 ½ Hr. 1.7 1.6 1.4 4-24 Hr. 1.4 1.3 1.2
