Direct measurement of Voltage in high voltage system is not possible because of insulation problem of measuring instruments. It is also not possible to use voltage through the system directly for protection purpose due to its high value & high insulation problem. In such conditions voltage transformers are used.

The transformers are oil filled, assembled in M.S.Tanks & Chambers together with suitable Porcelain Bushing. High quality C.R.G.O. Silicon Steel is used in the transformer. High quality kraft & crepe insulating paper is used to build up main insulation. Semiconducting shield is used to give linear distribution of Electrical stress along the length of the bushing. Filtered & de-aerated EHV grade oil is filled in VTs while VT is under vacuum. To seal it, the space left for expansion on the top is filled with dry & pure Nitrogen through non returnable valve at pre-determined pressure.
Design incorporating Stainless Steel Bellows instead of Nitrogen cushioning is also available.