{'fraction_non_alphanumeric': 0.010238907849829351, 'fraction_numerical': 0.011092150170648464, 'mean_word_length': 5.23936170212766, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
An Investigation Into the Drying of Distribution Transformers Using the Hot Air Vacuum Method


 A hot air vacuum method with considerable difference in design and constructional features as compared with the conventional process of a normal convection oven has been built and operated for drying transformers up to 1000 kVA, 33 kV. Moisture-equilibrium charts for kraft paper were used for designing the drying system. A high temperature air circulation fan placed inside the vacuum chamber simplified the construction and using air ducts directed at the transformer inside the autoclave improved the heat transfer capability and reduced the heating time for the transformer. A dry vacuum pump used for moisture removal eliminated the need for condensing water vapour before exhausting it into the atmosphere. A mathematical model for predicting the heating and vacuum cycle for distribution transformers in the autoclave has been presented with reasonably accurate results. Experimental results give a 1% or less moisture content in the insulation after dryout in about 10–12 hours. This indicates energy savings over a conventional air circulation process of about 70%.