A very specific requirement calls for pacement of trnasfoirmer at underground while the cooling equipment is at a height of 35 meters above the trnasformer . So , the complete tank and acessories like PRV and OLTC are at a pressure equivalent to 35 meter height of oil column .While we are going ahead with the design of the transformer we expect some problem with the PRV and OLTC ( we prefer vaccum type OLTC )