Outdoor oil cooled instrument transformers are paper insulated oil impregnated type insulation & Winding is done by automatic machines in extremely controlled dust free environment.
Outdoor oil cooled instrument transformers are hermetically sealed type in construction. The whole CT/PT unit is dried in an air heating oven under very high vacuum & strictly controlled conditions. Measurement of amount of moisture taken out from the CTs/PTs is done at regular intervals during the vacuum drying process. After the process is over the CT/PTs are filled with filtered, de-aerated EHV grade transformer oil under vacuum. The oil filtration plant, the processed oil storage tank & the vacuum drying chambers are all interfaced together to ensure that the CTs/PTs are filled with oil untouched by human hand. To seal the CT/PTs the space left for expansion on the top is filled with dry & pure -nitrogen gas through a non -returnable valve at pre determined pressure.
On request Mehru can also supply CTs/PTs with stainless steel bellows instead of nitrogen gas cushioning.