Outdoor current transformers

Figure 15.15(b) 400 kV bar primary outdoor current transformer (Courtesy BHEL)... 

For outdoor installations the recommended minimum creep distances for all types of voltage or current transformers are given in Table 15.1, according to lEC 60044-1 or lEC 60044-2. 

Outdoor high- aud medium-voltage substations usually employ oil-immersed circuit breakers as a system protective device. These devices are equipped with direct-acting internal current transformers and trip coils enclosed in a jacket filled with a mineral oil. The oil jacket provides rapid coohng for contacts which become heated due to arcing action created by each switching operation. The oil-Med jacket is a better heat dissipator than air, so the device can be smaller than one which is air-cooled. 

Since the production of PCBs ceased in the late 1970s in North America and Europe, current atmospheric sources of PCBs are believed to be predominantly from volatilization from contaminated environmental surfaces such as soil [312-314] and water [291, 315]. However, emission from existing PCB technical mixtures (i.e. capacitors, transformers, constmction materials) may also contribute to atmospheric contamination [316, 317]. The use of PCB atropisomers for source apportionment was first demonstrated by Robson and Harrad [182], who observed that nonracemic soil EFs for PCBs 95, 136, and 149 were statistically different from racemic EFs of all three congeners in the overlying air. In contrast to chiral OC pesticides, the source of atmospheric PCBs was thus not due to volatilization from the sod, but from emission of unweathered PCBs remaining in use. In subsequent work [318], PCB concentrations of indoor air in the West Midlands of the UK had not changed significantly over the past 10 years. Both indoor and outdoor air had... 

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