What are the allowed values of Tan Delta for (a).Transformer Oil (b).Windings - for oil immersed,for Winding with dry type insulation (c)Bushings - for Plain bushings, for Condensor bushings.(d) CT & PT

Tan delta limit for CT, PT, CVT bushing and Oil is 0.5% but it depends upon the manufacturer and type of material used.Fat results and commissioning testing results are provided for this purpose. If no previous results are available then by comparing same type of equipment is helpful in assessing. Trending rather than exact values are more beneficial for condition assessment of equipment. The capacitance of transformer bushing should not vary more than 5-10 % of name plate same is the case with CVT and CCVT. Tan Delta for transformer winding should not exceed 0.5 % at 20 C. For dry type transformer tan delta between High to low should be less than 2%, HG should be less than 3% and LG should be less than 4 %